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In this paper, an extension of the Timoshenko model for plane beams is outlined, with the aim of describing, under the assumption of small displacements and strains, a class of dissipative mechanisms observed in cementitious materials. In the spirit of micromorphic continua, the modified beam model includes a novel kinematic descriptor, conceived as an average sliding relevant to a density of micro-cracks not varying along time. For the pairs of rough surfaces, in which such a distribution of micro-cracks is articulated, both an elastic deformation and a frictional dissipation are considered, similarly to what occurs for the fingers of the joints having a tooth saw profile. The system of governing differential equations, of the second order, is provided by a variational approach, endowed by standard boundary conditions. To this purpose, a generalized version of the principle of virtual work is used, in the spirit of Hamilton–Rayleigh approach, including as contributions: (i) the variation of the inner elastic energy, generated by the linear elasticity of the sound material and, in a nonlinear way, by the mutual, reversible deformation of the asperities inside the micro-cracks; (ii) the virtual work of the external actions consistent with the beam model, i.e., the distributed transversal forces and the moments per unit lengths; besides these two contributions, constituting the conservative part of the system, (iii) the dissipation due to friction specified through a smooth Rayleigh potential, entering a nonlinear dependence of viscous and Coulomb type on the sliding rate. Through a COMSOL Multiphysics implementation, 1D finite element analyses are carried out to simulate structural elements subjected to three- and four-point bending tests with alternating loading cycles. The dissipation of energy is investigated at varying the model parameters, and the predictions turn out to be in agreement with preliminary data from an experimental campaign. The present approach is expected to provide a valuable tool for the quantitative and comparative assessment of the hysteresis cycles, favoring the robust design of cementitious materials. [ABSTRACT FROM AUTHOR]

Acidic contaminants are one of the major pollutants that penetrate the soil through various pathways, such as breaking pipes, factory effluents, and chemical leakages. In this study, systematic static and cyclic simple shear tests were performed to explore the behavior of marine sands subjected to acidic conditions, considering the influences of the different cyclic stress ratios and acid erosion durations. The peak shear strength, pore pressure, deformation, stiffness degradation, damping ratio, and liquefaction resistance were investigated. Test results show that increasing the acid erosion duration causes an increase in the monotonic peak shear strength, a decrease in the rate of pore pressure build-up, and enhances the liquefaction resistance of marine sands. The liquefaction resistance of tested marine sands subjected to acid erosion is about 1-1.2 times greater than that of sands without acid erosion. On this basis, a modified model was established to predict the pore pressure generation of marine sands, and an assessment method of the liquefaction resistance suitable for marine sands that is independent of the acid erosion duration was obtained, providing an effective means for early evaluation of soil liquefaction in engineering practice. Furthermore, by carrying out an energy-based assessment of liquefaction behavior, a unique correlation between various cyclic behaviors and dissipated energy was revealed, indicating the potential applicability of the energy-based method for evaluating the characteristics of marine sands even under acidic conditions. [ABSTRACT FROM AUTHOR]

The fracture surface regarded as the three-dimensional morphological characteristics of crack propagation is formed under the impetus of energy, and its characteristics can be described by the fracture surface roughness. Investigating the fracture surface roughness is of high importance for prediction and assessment of earthquakes, calculating shear strength at the fracture zone, and comprehending fluid flow. However, an excess of available energy flowing to the crack tip would cause crack branching, and the influence of the energy on fracture surface roughness of branching is rarely considered. This paper aims to evaluate the effect of the dissipated energy on fracture surface roughness based on rock dynamic fracture experimental study of crack branching. A set of split Hopkinson pressure bar measuring systems (SHPB-PS50) for rock dynamic fracture tests was established. The morphological characteristics of crack branching on the specimen surface, the three-dimensional surface topography of the fracture surface, and the changes in the dissipated energy characteristics with the fracture surface roughness were analyzed. It is concluded that the attenuation function is suitable for expressing the relationship between the roughness parameters and the dissipated energy, and an energy model with non-symmetrical branching of different roughness is established. Additionally, a numerical simulation analytical approach is developed for building the fracture surfaces through the coordinates of the discrete fracture network to measure roughness. The numerical simulation results support the experimental conclusions. The energy-based model with non-symmetrical branch fractures of different roughness is correct. [ABSTRACT FROM AUTHOR]

Test results of beam-column moment connections of storage racks are presented. Quasi-static tests were performed using a displacement-controlled electromechanical actuator on connections with two different bolting torques. The experimental setup contemplates a 1.48 m long column, labeled at both ends, and a 1.72 m long beam. The actuator has a 900 kg capacity load cell at its connection end with the beam and registers the applied deformation through a 300 mm travel displacement sensor. The beam was instrumented with rotation sensors, having one just before the support, and two in the L profile that connects it with the column. The loading corresponds to sawlike cyclic displacement sequences with increasing amplitudes, adapted from the AISC341 (2022) section K. The results showed that, by increasing the torque from 54.2 Nm to 108.5 Nm, the elastic stiffness increased by 45%. A higher tightening torque generated a reduction in pinching and an increase in the energy dissipated from the connection, compared to the case with lower torque. In general, the connections were capable of resisting rotations of up to 0.07 rad. [ABSTRACT FROM AUTHOR]

The biaxial tension–tension cyclic loading experiments were conducted on the cruciform specimens prepared using a silane‐modified polyurethane sealant to investigate their mechanical behavior. The finite element method was employed to validate the mechanical behavior of cruciform specimens under the biaxial cyclic loading conditions. It is shown that the highest stress concentration is in the central region of the cruciform specimens, indicating that the shape design of the specimen is suitable for the biaxial tension–tension cyclic tests. Additionally, the effects of loading path, mean stress, and stress amplitude on ratcheting strain and dissipated energy were analyzed through the experimental data. The experimental results demonstrated that the loading path had an influence on the mechanical behavior of the cruciform specimen. The additional ratcheting strain caused by the non‐proportional loading path was found to be loading path dependent of the adhesive. Moreover, the mean stress and stress amplitude greatly affected the strain response curves of the specimen under biaxial cyclic loading. The ratcheting strain and dissipated energy increased with increasing mean stress and stress amplitude; nevertheless, stress amplitude had more influence on the mechanical behavior than the mean stress. Highlights: The biaxial cyclic loading tests were conducted on the cruciform specimens.The effects on ratcheting strain and dissipated energy were analyzed.The loading path has influences on the mechanical response of the specimen.The mean stress and stress amplitude have effects on the strain response [ABSTRACT FROM AUTHOR]

The liquefaction of saturated marine coral sand is of a great issue for the safety of ocean engineering. A series of undrained cyclic torsional shear tests on saturated coral sand are carried out to further explore the liquefaction characteristics of coral sand. Based on the energy method, the effects of relative density (Dr), effective mean principal stress ( p ′ 0 ), and cyclic stress ratio (CSR) on undrained responses of saturated coral sand are investigated. Two failure criteria are discussed to evaluate the dissipated energy required to cause initial liquefaction (Wl). The test results show that the Wl is significantly affected by Dr and p ′ 0. The generation patterns of excess pore water pressure (EPWP) and single amplitude torsional strain amplitude (γSA) along with cumulative dissipated energy (Wc) are described, and the unified generation model of both ue and γSA along with Wc are established. The liquefaction resistance curves for various Dr and p ′ 0 are strongly related to Wl. Analyzing the cumulative dissipated energy required to trigger liquefaction, a modified stress level index termed CSRe is proposed to normalize the liquefaction resistance curves of saturated coral sand under different Dr and p ′ 0. The test data in literature also verify the applicability of CSRe. [ABSTRACT FROM AUTHOR]

Pond ash is a byproduct obtained from the combustion of coal in thermal power plants. It can be used as an alternative to conventional granular materials in compacted subgrade or subbase layers in pavements. The properties can be further enhanced by the addition of small doses of cement. Typically, the modulus parameters required for the design of pavements are based on resilient modulus models. Such models presume that the material attains a shakedown response in every loading sequence and the resilient modulus (MR) can be defined. However, it is not very clear whether a nonconventional material such as pond ash or cemented pond ash attains shakedown within 100 cycles of each sequence as stipulated in the resilient modulus test protocol. The number of loading cycles required to reach the shakedown limit is explored in this study. There are two sets of experiments conducted: the conventional resilient modulus tests with 100 cycles in each sequence and repeated load triaxial tests with 10,000 cycles for three confining pressures (41.4, 27.6, and 13.8 kPa) at a deviator stress of 69 kPa. The effect of cement dosage (2% and 3%), compaction condition (standard and modified Proctor compaction), and water content (optimum moisture content (OMC), OMC−2%, and OMC+2%) were studied. The shakedown theory is explained in terms of permanent deformation increment per cycle, dissipated energy, and tangent modulus. The resilient modulus is defined as the tangent modulus of the material which has attained shakedown. The cemented pond ash did not strongly correlate to confining pressure and hence, a constant value of the resilient modulus may be used. [ABSTRACT FROM AUTHOR]

Dynamic mechanical characteristics of coral sand is of vital importance for foundation compaction. In the present study, a series of tests were conducted to estimate the dynamic behaviors of coral sand under drop weight impact. The coral sands with original and uniform gradations were impacted with different energies and different repeating times. The test results show that the dynamic force–displacement or the stress–strain response roughly undergoes the initial intense fluctuation, quasi-free fall, subsequent descending fluctuation and the inverse rebound periods. The reduction in the void ratio of coral sand increases with single impact energy increasing, while it decreases with the repetition of impact. The breakage of coral sand under impacting is progressive along the height of the sample, revealing by the multiple yield points in the e-logp curve. It is found that the predominant size fraction of fragmented particles corresponds well to the inflection interval of its initial PSD curve. The ratio of the dissipated energy to the absorbed energy generally reduces as the repetition of impact loading. The breakage index can be closely correlated to the dissipated energy. As compared to the original coral sand, the uniform coral sand exhibits more sensitive behaviors in terms of compressibility, particle crushing and energy dissipation. Furthermore, the scenario of few impacts at high energy level is proved to be more efficient than that of multiple impacts at low energy level in the reinforcement of coral sand. [ABSTRACT FROM AUTHOR]

Waste-tire textile fibers (WTTF) represent a challenge for the recycling industry since there are currently very few alternatives for their use. In this study, an evaluation of the effect of a new additive developed in two granular formats from WTTF on the fatigue behavior of asphalt mixtures was performed. For the first format of the WTTF-based additive, its effect was evaluated on hot-mix asphalt (HMA), while for the second format of the additive, the effects were evaluated on stone mastic asphalt (SMA). This second format represents an alternative that allows for the total replacement of the cellulose stabilizing additive used in the reference mix. The evaluation of fatigue damage in the mixes was performed using the four-point bending beam (4PB) test specified in European standard EN 12697-24. The test results show that the asphalt mixtures manufactured with WTTF-based additives exhibited a higher capacity to resist load cycles before failure compared to the reference mixtures. Likewise, once the asphalt mixtures were evaluated in a pavement structure by means of an empirical mechanistic analysis, the pavement structures composed of asphalt mixtures with WTTF-based additives showed significant improvements in their durability for the different load axes evaluated. For an average thickness of 15 cm of asphalt mix of a pavement-type structure, the use of the WTTF additive increases the durability of the structures by up to 129% and 112% compared to the HMA and SMA reference mixtures, respectively. These results show that both formats of the WTTF-based admixture improve the fatigue damage resistance of the HMA and SMA asphalt mixtures. [ABSTRACT FROM AUTHOR]

In the fatigue design and analysis of concrete structures, an understanding of the dissipated energy characteristics of the material under cyclic loading is important. However, due to the heterogeneity of concrete, the quantitative analysis of dissipated energy is extremely challenging. To investigate the evolution characteristics and influencing factors of dissipated energy, a series of fatigue tests were conducted. Four variable-amplitude cyclic loading schemes were designed to study the relationship between dissipated energy and stress levels, loading frequency, and loading history. The results show a three-phase characteristic of falling-stable-rising in the evolution of single-cycle dissipated energy. The steady value in the second phase is related to the fatigue damage accumulation rate and presents an exponential function with the maximum and minimum stress level. A stress level of 0.75 is considered as the threshold for evaluating the effect of loading history on fatigue damage. The total energy dissipated in the fatigue test has a lower limit close to the energy absorbed in the static test. The relationship between the total dissipated energy and the fatigue life can be described by a linear function in logarithmic coordinates. Based on the evolution characteristics of dissipated energy, a nonlinear fatigue life prediction formula was proposed from the linear damage accumulation model. This study is of great significance for the development and application of the energy-based concrete fatigue damage models. [ABSTRACT FROM AUTHOR]

This research analyzes the fatigue behaviours of asphalt mixture under haversine wave and two more realistic loading waveforms induced by the single axle and tandem axles, based on the pseudo-strain-based approaches. It is found that the fatigue lives of asphalt mixture under the single-axle wave are higher than those under the haversine wave, while the tandem–axle wave generates the lowest fatigue life. This fact suggests testing asphalt mixture using the actual loading waves occurring in the field to improve fatigue life prediction of the asphalt layer. Three PSE-related indicators, namely initial dissipated PSE, cumulative dissipated PSE and the average changing rate of PSE per cycle, all generate a unique linear relationship with the mixture's fatigue life on the log–log scale. The linear relationship is independent of strain level and loading waveform. The damage characteristic curves of asphalt mixture obtained from the VECD approach are independent of strain level but affected by loading waveform. One of VECD-related indicators named DR stays stable as the loading wave or strain level changes, while another indicator named Sapp changes considerably at different waves and strain levels. The latter indicator shows the high potential to predict the asphalt mixture's fatigue life. [ABSTRACT FROM AUTHOR]

In this paper, the mechanical damage characteristics and energy dissipation patterns of fibre-reinforced cemented tailings backfill (FRCTB) under different strain rates are investigated based on the Hopkinson pressure bar apparatus equipped with confining pressure facilities, and this investigation is conducted by combining the theories of box fractal dimension and energy dissipation. The findings reveal notable observations: under lower confining pressures, the strain rate strengthening effect exhibits pronounced influences on both failure patterns and energy dissipation. However, as the confining pressure escalates, the strengthening effect gradually diminishes. The dissipation energy density displays an increasing trend with the rise in confining pressure, while the energy dissipation rate exhibits a quadratic decline as the strain rate increases. The stress-strain curves of FRCTB, under both unconfined and confined conditions, can be subdivided into four and five distinct segments, respectively. Under the lower confining pressure conditions, the fractal dimension exhibits linear growth with the increasing dissipation energy. As the confining pressure increases, this trend gradually transforms into a cubic function. Remarkably, a strong resemblance emerges between the fractal dimension, energy dissipation rate, strain rate, and confining pressure, reflecting the intricate interplay among these crucial mechanical parameters. [ABSTRACT FROM AUTHOR]

The fracture features of shape memory alloy samples (nitinol) under low-cycle fatigue with different load frequencies (0.1; 1 and 10 Hz) were investigated. The frequency dependences on the number of cycles before the samples fracture, the maximum, and the residual deformation before and after their fracture, respectively, were analyzed. The maximum value of the dissipated energy in the load cycle decreases with an increase in frequency from 0.1 to 10 Hz. Fractography showed that the mechanism of samples fatigue failure depends on the loading frequency. At high frequency classical fatigue striations decorated with secondary cracks dominated at the nitinol fracture surface. While at low frequency, a special type of striated relief with alternate changes in the striation spacing and the orientation of shear planes, in which a local crack growth occurred in the loading cycle, were found. The appearance of fatigue striations was explained by phase transformations inherent in nitinol, due to the rearrangement of its crystal lattice at the crack tip with multiple direct and reverse phase transformations (austenite→martensite→austenite), respectively which occur in half-cycles of loading and unloading of samples. [ABSTRACT FROM AUTHOR]

This study explores the hysteresis phenomenon in DPPC (1,2-dipalmitoyl-sn-glycero-3-phosphocholine) monolayers, considering several variables, including temperature, compression and expansion rates, residence time, and subphase content. The investigation focuses on analyzing the influence of these variables on key indicators such as the π-A isotherm curve, loop area, and compression modulus. By employing the Langmuir–Blodgett technique, the findings reveal that all the examined factors significantly affect the aforementioned parameters. Notably, the hysteresis loop, representing dissipated energy, provides valuable insights into the monolayer's viscoelasticity, molecular packing, phase transition changes, and resistance during the isocycle process. These findings contribute to a comprehensive understanding of the structural and dynamic properties of DPPC monolayers, offering insights into their behavior under varying conditions. Moreover, the knowledge gained from this study can aid in the development of precise models and strategies for controlling and manipulating monolayer properties, with potential applications in drug delivery systems, surface coatings, as well as further investigation into air penetration into alveoli and the blinking mechanism. [ABSTRACT FROM AUTHOR]

Colloidal silica (CS) grouting is a soil improvement technique for seismic liquefaction risk mitigation consisting of the injection of a time-hardening, colloidal silica–based grout into potentially liquefiable sandy soils. A published laboratory test database—consisting of cyclic undrained triaxial tests on liquefiable clean untreated sand and on sand stabilized by 5% CS under different levels of initial stress anisotropy—is here discussed following an energy-based approach. The test results are presented and analyzed in terms of dissipated energy during cyclic loading. The obtained results show that (1) the development of dissipated energy is clearly related to the buildup of residual extra pore water pressure only for untreated sand samples; (2) under the same testing conditions, the dissipated energy at failure is significantly higher in stabilized sand than in untreated sand; and (3) the dissipated energy at failure is found to be independent of the cyclic stress amplitude and dependent on the degree of initial stress anisotropy for the untreated sand, while opposite trends are observed for stabilized sand. Therefore, contrary to the untreated sand, there is no evident advantage for using the dissipated energy at failure to assess the capacity of the stabilized sand. [ABSTRACT FROM AUTHOR]

An approach to determine the specific energy dissipated during cyclic loading of metal alloys with load ratios between 0 and 1 is developed. The dissipated energy per cycle is determined by using a limiting procedure to obtain the area enclosed between successive loading and unloading curves and can be used for low‐, medium‐, and high‐cycle fatigue. Comparisons with published data from two aluminum, one titanium, and one steel alloy show that the predictions capture the test results very well. A universal curve relating cycles to failure to two nondimensional parameters is derived. It is shown, in some limiting cases, that the method leads to power law equations with the parameters in these equations determined directly from the complete stress–strain curve of the material with no need to fit experimental data. Furthermore, if certain conditions are satisfied, the method is consistent with the existence of an endurance limit and Miner's rule. Highlights: Model describing the shape of loading and unloading curves during fatigue is developed.A closed‐form expression for the fatigue cycles to failure initiation is obtained.A single master curve for fatigue is created in terms of two variables.Comparisons with test results for four alloys show good to excellent agreement. [ABSTRACT FROM AUTHOR]

Surrounding rock deformation and consequent support failure are the most prominent issues in red-bed rock tunnel engineering and are mainly caused by the effects of unloading, rheology, and swelling. This study investigated the mechanical responses of two kinds of red-bed mudstone and sandstone under unloading conditions via laboratory observation. Volume dilation was observed on the rocks during unloading, and the dilatancy stress was linear with the initial confining pressure. However, the ratios of dilatancy stress to peak stress of the two rocks kept at a range from 0.8 to 0.9, regardless of confining pressures. Both the elastic strain energy and the dissipated energy evolved synchronously with the stress–strain curve and exhibited conspicuous confining pressure dependence. Special attention was paid to the evolution behavior of the dilatancy angle. The dilatancy angle changed linearly during unloading. When the confining pressure was 10 MPa, the dilatancy angle of mudstone decreased from 26.8° to 12.5° whereas the dilatancy angle of sandstone increased from 34.6° to 51.1°; when the confining pressure rose to 25 MPa, the dilatancy angle of mudstone and sandstone decreased from 45.8° to 17.4° and increased from 21.7° to 39.5°, respectively. To further understand the evolution of the dilatancy angle, we discussed the links between the variable dilatancy angle and the processes of rock deformation and energy dissipation. [ABSTRACT FROM AUTHOR]

There has been little research on the impact resistance of mortar–rock slope protection structures. To ensure that the mortar–rock interface has good adhesion properties under the action of impact loading, in this paper, based on fracture mechanics theory, a theoretical impact model was established for mortar–rock binary material. Dynamic fracture tests were carried out on mortar–rock interfaces using the split-Hopkinson pressure bar (SHPB) system. The Brazilian disc (CSTBD) specimen was prepared with one half in granite and the other half in mortar. The specimen used for the dynamic impact test was 48 mm in diameter and 25 mm thick. The effects caused by the change in interface inclination and interface shape on the dynamic fracture mode were discussed. The dynamic model parameters were obtained for different inclination angles and interfaces. The results show that both the interface inclination and interface shape have significant effects on the dynamic mechanical properties of the mortar–rock binary material. The fracture modes of the mortar–rock specimens can be classified into three types. When the interface inclination is 0°, the specimen shows shear damage with an interface fracture; when the interface inclination is in the range of 0–90°, the dynamic splitting strength of the mortar–rock material increases with increasing interface inclination, and the interface undergoes composite fracture; and when the interface inclination is 90°, the dynamic splitting strength of the specimen reaches its peak, and the interface undergoes tensile fracture. The mortar–rock interface damage follows the M-C criterion. The roughness of the interface shape has a large influence on the dynamic splitting strength of the specimens. The rougher the interface shape, the higher the interface cleavage strength and the higher the peak load that causes the material to damage. The results of this study can provide a reference for the design of mortar–rubble structures to meet the demand for impact resistance and have strong engineering application value. [ABSTRACT FROM AUTHOR]

During the service life of marine structures, environmental loads, such as earthquakes and ocean wave storms, may exert dynamic shear stresses of different amplitudes and orientations in the foundation soil. To investigate the undrained cyclic behavior of marine soft clay under a complex shear stress state, a laboratory study was performed on remolded clay specimens using a variable-direction dynamic cyclic simple shear system, through which two mutually perpendicular shear stresses can be simultaneously applied to the specimen within the horizontal x–y plane. Stress paths of linear, circular, and elliptical patterns were obtained by adjusting the amplitude ratio (η) between the two cyclic shear stresses and applied to investigate the undrained behavior of soft clay. The undrained cyclic responses of the clay specimens were presented and then analyzed from the viewpoint of energy dissipation. A strain-softening phenomenon was observed when the cyclic effective stress path reached the failure line determined by the monotonic test. The cyclic strength of clay subjected to multidirectional cyclic shear stresses (i.e., circular and elliptical stress paths) was 0.775η times that under unidirectional shear stress (i.e., linear stress path). The coupling effects of CSR and η on the cyclic strength and accumulation of residual pore water pressure can be uniformly correlated to energy dissipation. [ABSTRACT FROM AUTHOR]

This study experimentally investigates ordinary concrete under discontinuous cyclic compression loading and performs numerical simulation of the residual stress. The stress cycles in discontinuous cyclic compression tests are interrupted by zero or very low loading intervals (ZLIs). The fatigue tests revealed that the dissipated energy and unloading deformation modulus of a cycle after the ZLI (A cycle) are significantly higher than those of the cycle before the ZLI (B cycle). The dissipated energy and unloading deformation modulus increase with an increase in the stress level. The cumulative rate of fatigue damage in the A cycles is noticeably higher than that in B cycles. The mechanism of discontinuous fatigue is influenced by the residual stress caused by an uncoordinated mechanical response. Moreover, the simulation results indicated that stress concentration occurs in the interfacial transition zone between the aggregate and the cement paste matrix, and the residual stress and plastic deformation increase as the difference between the elasticity modulus of the aggregate and the matrix increases. [ABSTRACT FROM AUTHOR]

Coal seams are often affected by gas effects in addition to static and dynamic superimposed loads in the process of coal mining. Understanding the mechanical properties and energy dissipation of impacted coal under different initial gas pressures is extremely important. Therefore, dynamic compression experimentation of coal samples was conducted using a self-developed observable combined dynamic and static loading test system of gas-bearing coal. Furthermore, based on the crack volume increment, the crack energy dissipation density (CEDD) was defined to measure the energy required for a unit volume of cracks under different gas pressures, and the following conclusions were drawn: the deformation of gas-bearing coal can be divided into the elastic stage, elastic‒plastic stage, plastic stage and failure stage, and the dynamic strength and secant modulus decrease with increasing initial gas pressure. The impacted coal contains annular parallel cracks that run through the cross section and axial splitting/thoroughgoing cracks, and the two forms of cracks become more obvious with increasing initial gas pressure. The reflected energy of gas-bearing coal increases and the transmitted energy, dissipated energy and energy dissipation ratio decrease with increasing gas pressure. In addition, the CEDD decreases with increasing gas pressure because free gas and desorbed gas participate in external expansion work at the moment of impact, which results in a decrease in the CEDD required for gas-bearing coal failure. These conclusions enrich the basic theory of the dynamic coal–rock–gas disaster induction mechanism and can provide theoretical support for the monitoring, early warning and prevention technology of dynamic disasters in composites. Highlights: An observable combined dynamic and static loading test system of gas-bearing coal is successfully developed. Considering the strain–stress-dissipated energy curve of gas-bearing coal, the time-dissipated energy curve can be divided into the elastic stage, elastic‒plastic stage, plastic stage and failure stage. The relationship between the crack energy dissipation density (CEDD) of impacted coal samples and the initial gas pressure is clarified. The reason for the decrease in the CEDD with increasing gas pressure is revealed. [ABSTRACT FROM AUTHOR]

The simultaneous generation, dissipation and redistribution of excess pore pressures within the layers of a soil deposit, due to a seismic event, can significantly modify the seismic response of the whole deposit. The reliable estimate of the excess pore pressure induced by shaking within the soil is important to predict the behaviour of the soil at a large scale, and consequently, earthquake effects on built environment. Recently, pore pressure energy-based models are developing. Despite several advantages, their calibration is generally complex. The paper aims to provide a simple calibration procedure of the pore pressure energy-based prediction model developed by Berrill and Davis (1985), in order to make easier and more common the use to practitioners. The energy-based model of Berrill and Davis (1985) has been calibrated in this study by means of a dataset of 46 undrained cyclic triaxial and simple shear tests carried out on different sandy soils. The best fitting procedure with the envelope of the experimental curves has been adopted. The experimental evidences show that the two parameters (α and β) on which the model depends, are linked and can be related to the results of CPT or SPT in situ tests. The paper introduces two relationships to compute the calibration parameters from the well-known equivalent cone tip resistance (qc1Ncs) or the corrected SPT blow count ((N1)60cs). The applicability of the proposed procedure at a large scale has been discussed interpreting the results of cyclic simple shear tests on undisturbed sandy specimens from an energetic perspective. The validity of the calibration procedure has been finally verified performing 1D non-linear site response analyses by means of DEEPSOIL code, reproducing two centrifuge tests and three case histories. The close matching between the simulations of the excess pore pressure time histories with the experimental data of the centrifuge tests, together with the simulated excess pore pressure profiles of three case histories compared with the results achieved by using another 1D non-linear code demonstrates the effectiveness of the simplified procedure to calibrate the pore pressure energy-based prediction model of Berrill and Davis (1985). [ABSTRACT FROM AUTHOR]

Fatigue damage of asphalt mixture is the amount of energy dissipated from the tested sample in cyclic fatigue tests. The fatigue cracking could be reduced by prevailing the dissipated energy that can be applied to clarify the decrease in flexural stiffness. This study investigates the effects of Reclaimed Asphalt Pavement (RAP) and strain level on the fatigue life and dissipated energy concepts of the asphalt mixtures. Thirty-six beams were prepared and tested at a constant strain loading mode with 0%, 30%, 50%, and 100% content of RAP at a temperature of 20 °C and frequency of 5 Hz at three strain levels of 750, 400, and 250 micro-strain. Results show that the plateau value (PV) criterion seemed more feasible in estimating the fatigue performance of RAP mixtures and the dissipated energy approach is useful to understand fatigue testing under load-controlled mode. Therefore, fatigue life can be projected without performing millions of load repetitions. [ABSTRACT FROM AUTHOR]

The physical and mechanical properties of rocks can be reduced significantly by an acidic environment, resulting in engineering weaknesses, such as building foundation instability, landslides, etc. In order to investigate the mechanical properties of rocks after hydrochemical erosion, a chemical damage constitutive model was established and used to analyze chemical damage variables and energy transformation. It is assumed that the strength of the rock elements obeyed Weibull distribution, considering the nonuniformity of rock. The chemical damage variable was proposed according to the load-bearing volume changes in the rock under water–rock chemical interactions. The chemical damage constitutive model was derived from coupling the mechanical damage under the external load and the chemical damage under hydrochemical erosion. In order to verify the accuracy of the model, semi-immersion experiments and uniaxial compression experiments of black sandy dolomite were carried out with different iron ion concentrations. Compared with the experimental data, the chemical damage constitutive model proposed could predict the stress–strain relationship reasonably well after water–rock interaction. The effects of water–rock interaction on the rock were a decrease in peak stress and an increase in peak strain. The peak strain increased by 4.96–29.58%, and the deterioration rate of peak strength was 0.19–4.18%. The energy transformation of the deterioration process was analyzed, and the results showed that the decrease in releasable elastic energy, Ue, is converted into dissipated energy, Ud, after hydrochemical erosion. [ABSTRACT FROM AUTHOR]

Magnitude scaling factors (MSFs) account for the influence of ground motion duration on liquefaction triggering in simplified stress-based models in which the duration of the motion is quantified in terms of number of equivalent stress cycles (Neq). Central to computing Neq and MSF is the relationship relating the amplitude of applied loading and the corresponding number of cycles to trigger liquefaction, that is, cyclic stress ratio (CSR)-NL curves. Based on empirical evidence (and mathematical convenience), CSR-NL curves are commonly assumed to plot as straight lines on log-log scales, with the line having a slope of −b. As such, the b -value is central to computing Neq and MSF and has a significant influence on computed normalized seismic demand in simplified liquefaction evaluations. It is widely assumed that the b -value varies significantly as a function of soil density. However, in this study a review of published laboratory data and analysis of constant-volume cyclic direct simple shear tests performed as part of this study were used to assess the dependency of the b -value on soil density and other factors. We show that the criterion used to define liquefaction triggering in laboratory tests and the nonlinearity of the CSR-NL curves can result in the apparent dependency of the b -value on soil density. However, using a consistent liquefaction criterion based on the cumulative dissipated energy in a unit volume of soil yields b -values that are relatively insensitive to changes in soil density. Published modulus reduction and damping (MRD) curves can be used to compute b -values using an energy-based framework; this yields more generalized and less test- and soil-specific b -values. As a result of these efforts, a b -value of 0.28 is recommended for computing Neq and MSF, independent of soil density. [ABSTRACT FROM AUTHOR]

In this paper, flexural fatigue test of self‐compacting concrete (SCC) with waste tire 0% and 20% rubber content was studied. Meanwhile, the acoustic emission (AE) was used to monitor the whole process of the fatigue. The results show the dissipation energy presents obvious three stages, which are similar to the stiffness attenuation. The plateau value (PV) of radio of dissipated energy change has a double logarithmic linear relationship with fatigue life. Moreover, there is a linear relationship between the dissipated energy and cumulative AE parameters at about half of fatigue life. At last, the relationship between PV value calculated by cumulative AE counts changes and fatigue life is determined. Therefore, AE technology can be used to monitor the fatigue evolution of concrete. [ABSTRACT FROM AUTHOR]

Salt caverns are used to store different energy sources, resulting in different periodic operating frequencies. To investigate the influence of the cycle frequencies on the mechanical behavior of rock salt, uniaxial stepped cyclic loading tests with successively decreasing, successively increasing and arbitrarily changing frequency were conducted. The deformation and dissipated energy under different frequencies were compared and analyzed. The test results demonstrate that the cycle frequency slightly affects the deformation evolution and that effect only appears when the adjacent frequencies change sharply (more than 50 times). The strain induced in one frequency stage (stage deformation) caused by high frequency is greater than that at low frequency. The dissipated energy is affected significantly by frequency. The individual dissipated energy decreases nearly as a power function with the frequency, while the stage dissipated energy shows the opposite trends due to the large increase of the loading cycles. In general, a quick injection and withdrawal is more dangerous for surrounding rock. The results are helpful for the operation of salt cavern used for energy storage. Highlights: A novel test method with good accuracy and reliability—'stepped varying frequencies at the same cyclic stress' is conducted to study the effect of frequency. Deformation of rock salt is slightly affected by the changing frequency. The individual dissipated energy decreases with the increase of frequency, while the accumulated dissipated energy in a frequency stage shows the opposite. The damage and deformation of the rock surrounding a salt cavern are relatively large when the cyclic loading is fast. [ABSTRACT FROM AUTHOR]

To determine whether damping induced by stirring granular materials can be adopted as passive damping, the efficiency of damping upon stirring granular materials was investigated experimentally and numerically. In the experimental approach, a cylindrical mixer with a flat blade was used. As the rotating axis of the blade was driven by a stepping motor through a four-bar linkage mechanism, the blade rotated sinusoidally. The rotational angle of the blade and the torque exerted on the axial shaft by the blade were measured using two types of sensors. The energy dissipated per cycle was determined by calculating the area surrounded by the loop in the plot of the torque versus the rotational angle. The effects of packing ratio, particle diameter, particle material and blade frequency on the energy dissipated were examined. In the numerical approach, the torque exerted on the axial shaft was calculated by the discrete element method. The predicted relationship between the torque and the rotational angle of the blade was compared with the relationship obtained from the experimental results. Moreover, the effect of the frequency of the blade on the energy dissipated per cycle was investigated on the basis of numerical results. [ABSTRACT FROM AUTHOR]

• An improved multi-channel singular spectrum analysis method is proposed, which is ranked by the standard spectrum of singular value energy. • A dissipated energy function is proposed that can be well used for the determination of the dominant oscillatory section of the grid. Moreover, this energy function can be effectively extended to power systems with power electronic devices. • The area equivalent model can be updated periodically using updated PMU data to accommodate topology changes. The identification of dominant oscillation paths is one of the key aspects in studying the stability of inter-area power grids. This paper proposes an improved multi-channel singular spectrum analysis (MSSA) algorithm combined with dissipative energy to identify dominant oscillation section in power systems. First, an improved MSSA method is introduced, which determines the order using the singular value energy spectrum and can effectively identify inter-area oscillation modes in power systems. Second, an energy function analysis method is proposed, which is well-suited for determining dominant oscillation section in power systems. This method is minimally affected by time-varying and nonlinear factors and allows for the visualization of generator states. Finally, the IEEE 68-bus system is used to construct an equivalent model, demonstrating the method's versatility. Simulation results validate the noise resistance, computational efficiency, and applicability to topology change scenarios of the proposed method. This method can accurately analyze inter-area oscillation modes and help to establish the dominant oscillation section. [ABSTRACT FROM AUTHOR]

Background: Cartilage is a mechanically highly stressed tissue in the human body and an important part of synovial joints. The joint cartilage is lubricated by synovial fluid with hyaluronic acid (HA) as main component. However, in joints with osteoarthritis HA has a lower concentration and molecular weight compared to healthy joints. In recent years, the intra-articular injection of therapeutic HA lubricant, has become a popular therapy. The effect of HA application on the friction of a complete joint with physiological movement needs to be further determined.Methods: The aim of the present study was to evaluate the lubrication effect of the joint by three lubricants (NaCl, fetal calf serum (FCS) and HA) and their effect on the friction in nine complete ovine carpo-metacarpal joints. The joints were mounted on a material testing machine and a physiological movement with 10° rotation was simulated with ascending axial load (100 - 400 N). Specimens were tested native, with cartilage damage caused by drying out and relubricated. Dissipated energy (DE) as a measure of friction was recorded and compared.Results: Investigating the effect of axial load, we found significant differences in DE between all axial load steps (p < .001), however, only for the defect cartilage. Furthermore, we could document an increase in DE from native (Mean: 15.0 mJ/cycle, SD: 8.98) to cartilage damage (M: 74.4 mJ/cycle, SD: 79.02) and a decrease after relubrication to 23.6 mJ/cycle (SD: 18.47). Finally, we compared the DE values for NaCl, FCS and HA. The highest values were detected for NaCl (MNorm = 16.4 mJ/cycle, SD: 19.14). HA achieved the lowest value (MNorm = 4.3 mJ/cycle, SD: 4.31), although the gap to FCS (MNorm = 5.1 mJ/cycle, SD: 7.07) was small.Conclusions: We were able to elucidate three effects in joints with cartilage damage. First, the friction in damaged joints increases significantly compared to native joints. Second, especially in damaged joints, the friction increases significantly more with increased axial load compared to native or relubricated joints. Third, lubricants can achieve an enormous decrease in friction. Comparing different lubricants, our results indicate the highest decrease in friction for HA. [ABSTRACT FROM AUTHOR]

In this study, the dynamic compressive strength and dissipated energy of rocks were investigated under hydrostatic pressure after different freeze–thaw cycles (FTCs). A split Hopkinson pressure bar (SHPB) with a lateral confining pressure chamber was used for the dynamic testing of sandstone specimens. The results indicated that under a certain loading rate and hydrostatic pressure, both the dissipative energy and dynamic compression strength of rocks decreased with the increase in the number of FTCs. The hydrostatic pressure significantly increased the dissipated energy and dynamic compression strength of rocks, and the enhancement became more pronounced as the number of FTCs increased. By analyzing the energy and damage characteristics of the specimens, after 40 FTCs, the internal damage of the specimens became critical and desensitized the dissipated energy to the loading rate. Based on the testing results, an empirical function was proposed to describe how the dissipated energy was related to the number of FTCs, hydrostatic pressure, and loading rate. It was demonstrated that the dissipated energy had a negative linear relation with FTC, which was enhanced by confinement. The dissipated energy of the specimen corresponded to the dynamic compression strength according to a quadratic function. [ABSTRACT FROM AUTHOR]

Vibrating technological equipment for the introduction of piles and columns into the ground of construction foundations (named vibratory piling machines) is crucial in the process of building stable and resilient foundations for civil engineering, hydrotechnical construction, special construction (e.g., military constructions), bridges, roads and industrial platforms. During the works carried out by the construction companies in various geographical areas of Romania, particularities of the dynamic technological regimes influenced by the nature of the land were identified at the deep introduction of the construction elements in the form of piles or circular (tubular) columns. The results of applied research, rheological modeling and optimization of vibrating equipment, highlight the need for an analytical approach that takes into account the parametric variations of the elastic and damping characteristics of some categories of soils on the depth of piles or foundation columns. In this context, the paper presents the calculation model with the dynamic response for the vibrating equipment of insertion with disturbing forces of 200–1250 kN for piles or columns with lengths of 10–30 m. The novelty of the research study consists in the linear rheological model, which was adopted in the form of a Maxwell–Voigt–Kelvin schematic of the type (E-V)–(E|V), with a discrete variation in four values for stiffness and damping of the soil, as the piles or columns vibrate and advance in the ground foundation. Practical experience of the authors in the field of using vibrogenerators for the introduction of piles in various types of ground foundations led to the adoption of the rheological model with variable damping coefficients depending on the depth of penetration into the soil. The curves of the dissipated power confirm the experimental data obtained in situ, in accordance with the rheological indoor tests of the different types of soil foundations. [ABSTRACT FROM AUTHOR]

• Fretting wear is observed to accelerate crack growth of SPR joint. • A dissipated energy method in consideration of stress concentration factor is presented to predict fatigue life of SPR joint. • Anti-fatigue optimization design of SPR joint with two rivets is performed by multi-island genetic algorithm method. The dissimilar aluminum alloy plates would be pierced by rivet, and the irreversible deformation results in fatigue life reduction of self-piercing riveted joint, compared with the base material. In order to exactly estimate the remaining life of self-piercing riveted dissimilar aluminum alloy joint, a dissipated-energy-based life span assessment method in consideration of stress concentration coefficient is presented in this paper. The mechanical properties of riveted joint and base material are obtained through monotonic tensile tests. Fatigue tests of self-piercing riveted joint are performed to capture surface temperature increment by the infrared thermal imaging technique, and fatigue failure analysis is conducted on the fracture surface. The stress concentration coefficient is determined by the numerical analysis of SPR joint under tensile loading, and then a novel dissipated-energy-based lifetime estimation approach is suggested. The predicted lifetime of self-piercing riveted joint agrees well with the tested data. The optimization design of self-piercing riveted joint with two rivets is implemented by considering the uncertainties of the rivet position to extend lifespan, and the calculated results show that the fatigue life of the optimized riveted joint improves by 68.2%. [ABSTRACT FROM AUTHOR]

Understanding the fatigue failure mechanisms in concrete is complex and remains an area of ongoing investigation. Material heterogeneity, along with the size effect, plays a significant role in specifying the crack propagation behaviour and fatigue life in case of repetitive loading conditions. In this study, the influence of material heterogeneity on the fatigue behaviour of concrete has been examined. Three different-size beam specimens with varying heterogeneity (aggregate sizes) have been considered to investigate various fracture characteristics under repetitive load conditions. Acoustic emission and digital image correlation techniques have been employed to analyse crack growth behaviour. The results revealed that stiffness degradation and crack propagation rates are faster for the specimens with smaller aggregate sizes compared to the larger aggregate size specimens of the same depth. Moreover, the fatigue life and effective crack length at failure are also higher in the case of larger aggregate sizes compared to smaller ones. Therefore, a heterogeneity-adjusted, analytical model of fatigue crack growth has been proposed. Further, the AE parameters have been utilized to characterize the tensile and shear crack dominance in different stages of fatigue crack propagation. The outcome of this study can be utilized to anticipate the crack propagation behaviour and residual fatigue life for any combination of specimen size and aggregate size. • The present study focuses on fatigue analysis in concrete considering material heterogeneity. • The work considers three different specimen sizes and aggregate sizes to demonstrate its influence. • The research proposes a heterogeneity adjusted fatigue crack growth model for concrete. • AE parameters have been utilized to characterize the tensile and shear crack dominancy. [ABSTRACT FROM AUTHOR]

This work introduces a new methodology to predict the fatigue life of viscoelastic materials by considering the creep effect on fatigue behavior under the concurrent effects of stress level, stress ratio, and temperature. The model established based on the total amount of energy dissipated during fatigue loading. To estimate the amount of dissipated energy under varying stress ratios and temperatures, two shift factors, ψ c y c l i c (R , T) and ψ c r e e p (R , T) , were derived, attributed to the cyclic and creep parts of fatigue loading. These shift factors were subsequently incorporated into defined equilibrium equations to create the relationship between estimated dissipated energy and fatigue life. The input data for the model consisted of the dissipated energy and cyclic creep values obtained from experiments conducted at a reference stress ratio of 0.5 and reference temperature of 20 °C, together with the storage and loss moduli measured from one dynamic mechanical analysis (D M A) experiment in the temperature range of 15 °C–60 °C on a fully-cured epoxy adhesive. To validate the accuracy of the results, the predicted fatigue life at three temperatures of 20 °C, 40 °C and 55 °C, each loaded under three stress ratios of 0.1, 0.5, and 0.9 were compared with the experiments conducted under the same conditions. Almost all predicted results were in good agreement with the experiments, nevertheless; at the stress ratio of 0.9 at 20 °C, due to the significant change in the cyclic creep behavior, the accuracy of the prediction was lower. The developed model was used as a new constant life diagram (C L D) formulation, which afterwards was further developed to plot three-dimensional constant life diagrams (3-D C L D s) in which the constant life surfaces were a synergistic function of stress ratio and temperature. • A novel model was introduced to predict the fatigue life of viscoelastic materials. • The proposed model predicts fatigue life based on the total amount of energy. • The model predicted fatigue life across various combinations of stress levels, stress ratios, and temperatures. • The developed model was used as a new CLD formulation. • A new three-dimensional Constant Life Diagrams (3-D CLD) was introduced. [Display omitted] [ABSTRACT FROM AUTHOR]

Ageing of bitumen changes its stiffness related properties and is thought to have a considerable impact on its fatigue performance. Time sweep tests are a commonly used methodology to evaluate the fatigue performance of bitumen over the course of its lifetime. This study comparatively evaluated the fatigue performance of six aged bitumen samples using various commonly employed time sweep testing-based approaches, including conventional methods (50% reduction in complex modulus and peak in phase angle) and newer methods (peak in S × N and two dissipated-energy-based approaches). The statistical analysis of the results illustrated that although the trends of fatigue life versus ageing levels were similar, different methods had significantly varying results. It was generally seen that ageing increased stiffness and the calculated fatigue life of bituminous binders improved when commonly applied strain levels of 5% and 7.5% were used. This result demonstrates the need to develop more robust methods to fully capture the true fatigue related deterioration of aged binders in the future. Among all the methods, the peak in S × N approach was found to be the most efficient based on the criteria used in the study and was the recommended approach considering current limitations. It showed no apparent defects and had the best correlations with other methods when the applied strains were 5% and 7.5%. • Commonly used time sweep testing-based fatigue evaluation methods were compared for six aged binders. • Different analysis methods show significant statistical differences. • S × N approach is recommended for time sweep testing-based fatigue characterisation. [ABSTRACT FROM AUTHOR]

[Display omitted] The squeezing deformation of deep soft rock tunnels is driven by energy. Few scholars have carried out theoretical research on energy evolution for deep soft rock tunnels. This study proposes a computational method for tunnel energy evolution in strain-softening rock mass during excavation unloading based on triaxial stress paths. The characteristics of energy distribution and energy evolution are further investigated. Results show that energy is input from the distant surrounding rock after tunnel excavation and converted into elastic strain energy in the elastic stage. In the plastic stage, the elastic strain energy density in the plastic zone reaches the storage limit, which is reduced due to the strain-softening behaviour. Thus the dissipated and released energy of the surrounding rock increases exponentially. For deep rocks with high peak strength, the energy evolution in the plastic stage is dominated by energy release, which indicates that rockburst mainly results from the energy release mechanism. In contrast, for the surrounding rock with low strength, the energy evolution during excavation unloading is dominated by energy dissipation due to the significant strain softening behaviour. Large squeezing deformation mainly stems from the energy dissipation mechanism. [ABSTRACT FROM AUTHOR]

The self-healing ability of asphalt material has a significant effect on improving fatigue life of asphalt pavement. The objective of this paper was to investigate the stage characteristics of fatigue damage of asphalt binder and its associated self-healing behaviours. Firstly, the rheological behaviour and fracture surface morphology were discussed to investigate the fatigue evolution characteristics of asphalt binders. Secondly, an effective method for interpreting the self-healing capability of asphalt binder at different fatigue stages was proposed by conducting fatigue-healing-refatigue tests and Fourier transform infrared spectroscopy analysis. Finally, the effect of temperature on the self-healing properties of different aging asphalt binders at different fatigue damage stages was explored. The results show that the stage characteristics of fatigue damage of asphalt binders could be distinguished effectively by correlating complex shear modulus with ratio of dissipation energy change under load time history. The fatigue cracking morphologies of asphalt binders under cyclic shear loading are susceptible to the aging degree of asphalt binder. An index associated with initial dissipative energy and number of cycles could effectively evaluate the self-healing properties of different aging asphalt binders. After the occurrence of macrocracks, the mechanical properties of asphalt binder cannot be completely restored by increasing the temperature. [ABSTRACT FROM AUTHOR]

By studying the key mechanical properties and their damage mechanisms of coal at the nanoscale, a better understanding of the strength and damage of coal in complex stress environments can be obtained. The micro-mechanical properties and damage mechanism of coal under cyclic loading were investigated by nanoindentation experiment and molecular dynamics (MD) simulation of nanoindentation. Molecular dynamics simulations were conducted by building models containing approximately 2.5 million atoms, it was found that the coal substrate showed cyclic hardening under cyclic loading. The hardness and elastic modulus of the coal samples measured by the nanoindentation experiment gradually increased from 0.476 GPa to 0.740 GPa and from 4.70 GPa to 5.997 GPa, respectively. The simulation results display a good agreement with the experimental results. The simulation results show that the plastic damage of coal substrate under cyclic loading is related to the stretching, bending, rotation, and fracture of chemical bonds. At the same time, the formation and recovery of elastic deformation are related to the changes of van der Waals force, Coulomb force, and bond angle. Additionally, the carbon hexatomic ring in the coal macromolecule is critical in resisting the influence of loading. [ABSTRACT FROM AUTHOR]

Based on the research carried out within the Research Institute for Construction Equipment and Technology—ICECON S.A. Bucharest, consisting of the design and development of vibrating-action machines and of the technical analysis of optimization of the technological processes with vibrating equipment for highway construction works in Romania. Moreover, the physical and mathematical modeling of this mechanical system used the data obtained in the activity of the certification of the technical level of capability of the processing equipment in industry and construction, taking into account the provisions of procedures and regulations legally enforced by normative documents. These are based on a parametric analysis of the dynamics of the technological processing vibratory equipment and machines. Thus, both the evaluation method and the parametric optimization procedure were established. In this context, this paper presents a numerical analytical approach with discrete and continuous parametric variations, from where favorable areas of operation can be established. In this way, the optimization criteria in stabilized harmonic vibration regimes are approached based on the assessment of the vibration amplitude, of the force transmitted to the processed material and of the energy dissipated in the system. The presented dynamic model as well as the specific parameters were used in the design and/or numerical and experimental assessment for vibrating rammers with the amplitude of the perturbing force from 2 kN up to 100 kN, vibrating compactors with the amplitude of the perturbing force from 100 kN up to 200 kN and vibrating sieves for mineral aggregates with surface sieves of 6, 12 and 18 sqm. The symmetry/asymmetry properties are specific to the dynamic response in steady-state technological regime. Thus, the amplitude of vibrations in resonance presents asymmetry through a functional level necessary for the technological regime. The maximum force transmitted in the technological process is asymmetric in relation to the variation of the excitation pulsation; also, the dissipated energy has asymmetries in the postresonance. Hysteresis loops are symmetrical to the main axis. The originality of the research results comes from the establishment of dynamic parameters for the amplitude of technological vibration, the force transmitted to the working part, the energy dissipated on the cycle, hysteresis loops in a steady-state regime with digital display to identify the dynamic regime and the damping in the system. The calculation relations are specific to machines with a vibrating action and, on their basis, the vibrating equipment from Romania were designed, manufactured and tested, as mentioned in this paper. [ABSTRACT FROM AUTHOR]

The fatigue performance of different warm‐mix recycled asphalt mixtures was evaluated by the semicircular bend (SCB) test. A delayed oven heating (DOH) method was developed to simulate the long‐term ageing in the laboratory. The effects of recycling plans, reclaimed asphalt pavement (RAP) content, and ageing levels on the tensile strength and fatigue resistance were investigated. The fatigue life of the warm‐mix recycled asphalt mixture was characterized by the phenomenological, dissipated energy, and the ratio of dissipated energy change (RDEC) models, respectively. The results show that the use of the warm‐mix asphalt (WMA) technology causes a reduction of the fatigue performance for the recycled asphalt mixture, which can be compensated by the addition of styrene–butadiene rubber (SBR) latex. As the RAP content or long‐term ageing time increases, the fatigue life significantly decreases. The dissipated energy model with the unified model coefficients can predict the fatigue lives for different warm‐mix recycled asphalt mixtures. HIGHLIGHTS: Fatigue performance of warm‐mix recycled asphalt mixtures was evaluated.A delayed oven heating method was developed to simulate the ageing in the laboratory.Effects of recycling plans, RAP content, and ageing levels were investigated.Different fatigue models were compared to predict fatigue lives of recycled mixtures. [ABSTRACT FROM AUTHOR]

The properties of fibre reinforced concrete were studied under monotonic loads according to Japanese, North American and European codes. Two different types of SIKA polypropylene fibre were with different dosages. One hundred and eighty tests were performed, obtaining resistance to compression, tension, bending, toughness, and energy absorption in the hardened state. The results show that the addition of fibres affects the workability of the concrete mix. The increase in fibre dosage does not affect compressive, tensile, or flexural strength. However, the failure changes from brittle to more ductile, allowing it to reach residual strengths of 50% of the maximum reached and 200% deformation. The dissipated energy increased with increasing fibre dosage. The performance achieved by both fibres was similar, although the optimal dosage was 6 kg/m³ for type A fibres and 8 kg /m³ for type B. Therefore, the replacement of flexural reinforcing steel in the foundation slabs of one-story buildings can be performed if adequate dosages are used in compliance with established analytical procedures for industrial floor design. [ABSTRACT FROM AUTHOR]

Stress-induced instability is associated with rock damage. Here, the progressive brittle fracturing process in Jinping marble is studied by introducing two types of true triaxial pre-peak unloading tests, namely, the incrementally cyclic loading-unloading minimum principal stress test (ICM test) and the incrementally cyclic loading-unloading maximum and minimum principal stress test (ICMM test). By comprehensively analysing the irreversible strains, dissipated energy, acoustic emission (AE) characteristics and scanning electron microscopy (SEM) results, the rock damage evolution can be quantified and divided into two distinctive damage stages. At the boundary point, the irreversible strain increments reach their minimum values. In the gentle damage stage, the normalized irreversible strains increase linearly, and this process is associated with a small number of AE hits with low amplitude. The rapid damage stage is characterized by a nonlinear increase in the normalized irreversible strains, and this process is associated with a large number of AE hits with high amplitude. The dissipated energy mainly increases in the rapid damage stage. In addition, the rapid damage stage in the ICMM test mainly occurs in the last five cycles, due to the differences in the deviatoric stresses in each cycle. In both of these tests, the failure mode is principally characterized by tensile failure. Moreover, the precursory signals of rock fracturing and the influence of the loading paths on the strength are discussed. [ABSTRACT FROM AUTHOR]

Moisture-induced damage in asphalt concrete is a major concern to the transportation agencies. Existing moisture sensitivity tests are mostly conducted at the macro- or micro-level and focused on the qualitative measurements only. In this study, the atomic force microscopy (AFM) technology is utilized to investigate moisture susceptibility of asphalt binders through the estimation of nano-level dissipated energy (DE). For the comparison of the AFM test results, two macro-level tests data are also used. Asphalt binders used in this study include a Performance Grade (PG) base binder (PG 64-22) along with its modified counterparts, which are blended with polyphosphoric acid (PPA), styrene–butadiene-styrene (SBS), and SBS plus PPA. Additionally, the effects of three different types of liquid anti-stripping agents (LAA) were investigated. The test specimens of these binder samples were prepared under dry and wet conditions, and their DE values were estimated from AFM tests. Results showed that the base binder and the PPA-modified binder had higher DE values than the SBS- or the SBS + PPA-modified binders. Among all the LAAs, Evotherm showed better resistance to moisture damage than the other ones. Findings of this study are expected to help highway agencies to quantify the moisture resistance of asphalt materials precisely. [ABSTRACT FROM AUTHOR]

Macroscopic frictional behavior of granular materials is of great importance for studying several complex problems associated with fault slip and landslides. The main objective of this study is to model the macroscale frictional behavior of granular soils under monotonic and cyclic loadings based upon micromechanical determination of dissipated energy at particle contacts. This study is built on the general observation that the externally computed energy dissipation should be equal to the total internal energy dissipation derived from inter-particle sliding and rolling, energy losses from inter-particle collisions, and damping. For this purpose, the discrete element method is used to model a granular soil and determine the stored, dissipated, and damping energies associated with shear loading for applied monotonic and cyclic velocities. These energies are then related to the friction by an application of the Taylor-critical state power balance relationship. Also, the contributions of the different modes of energy dissipation (normal, shear, and rolling) to the total frictional resistance were studied. By changing the inter-particle friction, the simulations showed that the macroscopic friction was nearly constant, the slip friction increased almost linearly with increasing inter-particle friction, and the difference between the two was attributed to the non-energy dissipating dilatancy component. By providing a clear relationship between energy dissipated by micro-scale mechanisms versus the traditional engineering definition based on macro-scale (continuum) parameters, this study provides a means to develop a better understanding for the frictional behavior of granular media. [ABSTRACT FROM AUTHOR]

The wide range of rivets usage goes back to the processes of manufacturing and repairing an aircraft fuselage. When it comes to structural joints, adhesive bonding is said to have some merits which overshadow other joining methods, such as bolting, riveting, and welding. Today, the applications of structural adhesives do not end in aerospace, but they also are ideal for the automotive industry, where the need is to join plates of dissimilar adhesives to produce lightweight car bodies. The hybrid joints also are one of the methods of joining different parts of the machine in a durable way in which some benefits such as the significant tensile strength, the dissipated energy, and higher reliability during long-term working stand out. In this research, the effect of rivets layout on strength and failure of nanocomposite rivet and hybrid adhesive-rivet joints through two experimental and numerical methods was evaluated. Also, using the artificial neural networks method, force–displacement curves for specimens were obtained. The results of the experimental tests and the finite element analysis showed that as the number of rivets increased in the joint of the nanocomposite components, the strength of the joint increased. The layout of the rivets has a significant effect on the strength of the rivet joint. According to the performed experiments for achieving the efficient strength in the hybrid joints for the nanocomposite plates, since the strength of the adhesive is very effective, adhesive selection and the appropriate number of rivets are the key factors. The fracture modes in the internal plates of nanocomposite joints (adhesive, rivet, and adhesive-rivet joints) were observed as follows: net-tension, bearing, shear-out, crack propagation, tearing, and shear in adhesive layers. Besides, the numerical model of the work is done using ABAQUS software. The results of software simulation in the numerical model are compatible with the experimental method's findings. However, the agreement between the results of experimental and neural network methods is higher. Owing to the results of experiments, the polypropylene nanocomposite as well as the appropriate jointing method can be put forward in the structures of the automotive industry. [ABSTRACT FROM AUTHOR]

An analytical framework was developed to correlate the intrinsic dissipation to the second harmonic of the temperature signal evaluated by means of the Fourier transform. The theoretical model assumes, without loss of generality, total conversion of the input mechanical energy into heat. Elastic‐perfectly plastic or elastic–plastic materials obeying a Ramberg–Osgood law are considered. For the sake of simplicity, analytical solution of the thermoelastic and plastic temperature evolutions are obtained in the case of uniform stress and temperature fields. It was found that the intrinsic dissipation is correlated to the second harmonic of the temperature signal by means of a parameter (the β parameter) that, in the case of an elastic–plastic material, depends on the cyclic hardening exponent n′. [ABSTRACT FROM AUTHOR]

The theoretical approach developed in the companion paper is applied to the temperature signals acquired by using an infrared camera, during step‐load fatigue tests carried out on AISI 304L cold‐drawn bars. The intrinsic dissipation, calculated according to the analytical model and by means of the discrete Fourier transform of the material temperature, is compared with that measured by using a well‐established experimental approach based on the measurement of the cooling gradient of the material temperature, after the fatigue test has been suddenly stopped. The results of this study indicate that the intrinsic dissipation calculated according to the two approaches become increasingly closer to one another for progressively higher applied stress amplitudes. [ABSTRACT FROM AUTHOR]

• This paper studies a new type of bending damage behavior of ceramic matrix composites. • Felicity ratio and dissipated energy characterize the internal damage of composites during different loading and unloading cycles. • 3D-C/C-TiC-Cu material has better flexibility and tensile strength in the vertical needling direction. In order to improve the matrix brittleness of carbon fiber reinforced ceramic matrix composites (CMCs), a new type of 3D-C/C-TiC-Cu CMC material is prepared by introducing high toughness Ti-Cu alloy. This study uses acoustic emission (AE) technology to investigate the damage process of the material under graded cyclic bending loading in order to study the mechanical properties of materials in parallel needling and vertical needling directions. Firstly, AE parameters are used to characterize the damage evolution process. Then, Felicity ratio and dissipated energy are used to characterize the internal damage of the composite during different loading–unloading cycles. Finally, RA-AF analysis based on the k-medoids algorithm is explored to reveal the effect of different needled fiber bundle directions on the cracking pattern of the composite. The results show that the AE count and the accumulated AE energy increase gradually with increasement of the number of loading cycles. Both the Felicity ratio and the dissipated energy of each loading–unloading cycle characterize the damage state of the material, and show that the damage in parallel needling specimens is more severe than in the vertical needling specimen. In addition, the tensile performance in parallel needling direction is lower than that in its vertical direction by the ratio of tensile and shear cracks obtained through RA-AF analysis. Thus, 3D-C/C-TiC-Cu material has better flexibility and tensile strength in the vertical needling direction. In practical application, the fiber direction of the material can be arranged according to the stress condition. [ABSTRACT FROM AUTHOR]

Growing environmental demands and higher fuel efficiency encourage the use of new light‐weight load‐bearing materials even for operation under rougher environmental conditions. Consequently, as the materials used in the vital load‐bearing components of the chassis, brake system or exhaust system are subjected to thermomechanical fatigue during the operation due to variable mechanical and thermal loads, it is crucial for design engineers and CAE analysts to understand the cyclic behaviour of new materials under such conditions. Here we have analysed the stress–strain behaviour of magnesium alloy AZ31 and the influence of variable thermomechanical loads. A uniaxially loaded flat specimen has been first mechanically loaded at −25°C. The temperature was then increased to 150°C whilst the variable mechanical loading remained unchanged. The tests have been strain‐controlled using a video extensometer. The stress–strain behaviour of the magnesium alloy AZ31 has been then investigated considering both variable temperature and variable mechanical load. [ABSTRACT FROM AUTHOR]