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A mathematical model has been developed to investigate the SIF (stress intensity factor) and COD (crack opening displacement) for the propagation of mode-III fracture influenced by propagating SH-wave in a pre-stressed dry sandy elastic continuum. The Wiener-Hopf mathematical method along with the Fourier integral transform (FIT) technique have been successively implemented to obtain the solution of the boundary value problem associated with the mathematical model. Furthermore, the closed form solutions of SIF and COD for non-static and static conditions of mode-III fracture have been obtained, and are found to be in well agreement with the existing results present in the literature. The sound effects of various affecting parameters viz. horizontal and vertical (compressive/tensile) pre-stresses, crack depth, and crack velocity on SIF and COD have been explored. In order to delineate the influences of these aforementioned parameters on SIF and COD graphically, numerical simulation has been accomplished. [ABSTRACT FROM AUTHOR]

The pre-stress of the temporomandibular joint (TMJ) at the intercuspal position (ICP) was often neglected, which would cause errors in the finite element analysis. The purpose of this study was to investigate the effect of pre-stress on dynamic finite element analysis of the TMJs. One healthy female adult was recruited for medical imaging and motion data acquisition of the reference position (RP) to the ICP and the clicking teeth. The three-dimensional maxillofacial model including the maxilla, mandible, articular cartilages, discs, and discal attachments was reconstructed. Motion from the RP to the ICP was simulated to obtain pre-stress at the ICP. Two groups of the clicking teeth were simulated: (1) the group without pre-stress (GWoP); (2) the group with pre-stress (GwP). Significant differences were found between the two groups at the initial moment of movement, during the open-mouth phase, and during the collision phase between the upper and lower teeth. The maximum difference in the discal contact stress between both groups was even more than double. The relaxation of the TMJ at the beginning of the mouth opening was simulated in the GwP. In addition, an increase in the TMJ stress during teeth tapping was simulated in the GwP. These were not reflected in the GWoP. If pre-stress at the ICP was not considered, part of the true results would be lost. It is necessary to consider pre-stress in the dynamic finite element analysis of the TMJ. [ABSTRACT FROM AUTHOR]

The radial propagation of the steady-state wave motion is studied for a pre-stressed cylindrical shell composed of the isotropic compressible neo-Hookean material. The radial static deformation of the cylindrical shell and radial wave motion of the pre-stressed cylindrical shell are investigated. The mathematical model is established as a class of boundary value problems of the second-order nonlinear ordinary differential equation (ODE). Based on the theory of the large elastic deformation superposed by the small harmonic deformation, a radial dynamic displacement is added to the pre-stressed cylindrical shell. The existence of the steady-state wave motion is conducted. Numerical solutions are obtained by using the multiple shooting method. In addition, the influences of the static load, material and structural parameters on the steady-state wave motion are discussed. Numerical results indicate that as the static load increases, the frequency of the steady-state wave motion increases and the amplitude decreases in the compressible hyperelastic cylindrical shell. The material parameter plays a significant role in the frequency and amplitude of the steady-state wave motion. [ABSTRACT FROM AUTHOR]

Seven simply supported steel beams were built and tested to provide a better understanding of how prestressed strands affect the steel beams’ behavior during the yielding stage. Steel beams had identical clear span lengths (2.85 m) and gross-section areas (3268 mm2). The strengthened sample was constructed using two external strands. The steel beams were divided into two types based on whether the exterior strand’s eccentricity was present or not. One of the steel beams serves as a reference. The remaining six steel beams were strengthened by external strands, which were divided according to the eccentric positions of the strands with the jacking stress (fpj = 815 MPa). It was found that strand eccentricity increase increased the ultimate load and yielding of tested strengthened beams. Also, the percentage of yielding to ultimate load ratio (Py/Pu) increased with the strand eccentricity. Finally, compared to the reference beam, the yielding strain positions for all tested beams shifted from the bottom to the top region, and all strain in the top and bottom zones were enhanced compared to the reference due to the external prestress strand, which improved the bottom and top flanges and the resistance of the web under the applied load.

We introduce a mathematical model for the mechanical behaviour of the eukaryotic cell cytoskeleton. This discrete model involves a regular array of pre-stressed protein filaments that exhibit resistance to enthalpic stretching, joined at cross-links to form a network. Assuming that the inter-cross-link distance is much shorter than the length scale of the cell, we upscale the discrete force balance to form a continuum system of governing equations and deduce the corresponding macroscopic stress tensor. We use these discrete and continuum models to analyse the imposed displacement of a bead placed in the domain, characterizing the cell rheology through the force–displacement curve. We further derive an analytical approximation to the stress and strain fields in the limit of small bead radius, predicting the net force required to generate a given deformation and elucidating the dependency on the microscale properties of the filaments. We apply these models to networks of the intermediate filament vimentin and demonstrate good agreement between predictions of the discrete, continuum and analytical approaches. In particular, our model predicts that the network stiffness increases sublinearly with the filament pre-stress and scales logarithmically with the bead size. [ABSTRACT FROM AUTHOR]

We propose the governing equations for a pre-stressed poroelastic composite material. The structure that we investigate possesses a porous elastic matrix with embedded elastic subphases with an incompressible Newtonian fluid flowing in the pores. Both the matrix and individual subphases are assumed to be linear elastic and pre-stressed. We are able to apply the asymptotic homogenisation technique by exploiting the length-scale separation that exists between the porescale and the overall size of the material (the macroscale). We derive the novel macroscale model which describes a poroelastic composite material where the elastic phases possess a pre-stress. We extend the current literature for poroelastic composites by addressing the role of the pre-stresses in the functional form of the new system of derived partial differential equations and its coefficients. The latter are computed by solving appropriate periodic cell differential problems which encode the specific contribution related to the pre-stresses. The model in the first instance is derived in the most general scenario and then specified for a variety of particular cases which are associated with different macroscale behaviour of materials. [ABSTRACT FROM AUTHOR]

Wave barriers are often used to reduce ground vibrations caused by different sources. As one type of wave barriers, periodic pile barriers have received broad attention from many researchers. However, most of the investigations are limited to single-phased soil. In many cases, soil behaves more closely to saturated medium due to the presence of groundwater. Wave propagation in saturated soil is quite different from that in single-phased soil. In addition, soil is usually pre-stressed when buildings sit on top of it. However, the impacts of pre-stressed soil on the vibration mitigation performances of wave barriers have not been investigated. To fill the above knowledge gaps, this paper investigates the vibration mitigation of plane waves by periodic pile barriers in saturated soil and considering the loads from the self-weight of the soil. The dispersion curves of the structure formed by piles periodically embedded in pre-stressed saturated soil are calculated. The impacts of some key factors on the first complete attenuation zone are comprehensively investigated. The frequency responses of both two-dimensional (2D) and three-dimensional (3D) models are calculated to verify the vibration reduction effectiveness of the wave barriers. Finally, the transient responses of a 2D model are investigated. The results and findings can be used to inform the design of periodic pile barriers to attenuate wave propagation or vibration with low and mid-frequencies in saturated soil. [ABSTRACT FROM AUTHOR]

Shrinkage and improper compaction of the repair layer are among the main reasons for the adhesion drop. Shrinkage results in cracking and improper compaction causes fine pores in the interface. Due to the fact that shrinkage and non-compacting are the main reasons for reducing strength and adhesion, therefore, in this paper, research has been done in this regard. The present study aimed to investigate the effect of polypropylene fibers on the shrinkage of mortars and bond of mortar/concrete interface. Moreover, the impact of diverse pre-stresses on the adhesion between mortar and concrete was evaluated by imposing pre-stresses on fiber-reinforced mortars. Adhesion was assessed by the “twist-off” and “pull-off” tests. Furthermore, the effect of fibers and pre-stress on the adhesion examined using SEM images and X-ray diffraction. It is necessary to assess the compressive strength of concrete and mortar in the field. Therefore, the aforementioned semi-destructive methods were employed to investigate the in-situ compressive strength of mortars at different ages. For this purpose, the correlation coefficient between the in-situ and laboratory methods was defined and the scaling curves were plotted to convert the in-situ test results into compressive strengths of the mortars. The obtained findings indicated the positive effect of pre-stress on adhesion. In addition to their mechanical effect, the indirect effect of fibers on the chemical properties of the mortars reduces shrinkage and augments adhesion. Moreover, given the great relationship among the conclusion of “pull-off” and “twist-off” methods, the cost-efficient and available twist-off apparatus can be used for adhesion measurement instead of the costly and import pull-off apparatus. Adding 0.3% of polypropylene fibers to the mortars enhanced the bond strength by 76.8% and 41.7%, respectively and reduced the shrinkage of the mortars by 11%. An initial stress of 0.5 kg/cm2 increased the shear and tensile bond strength at the age of 90 days by 12.8% and 13.3%, respectively.

Recently, Khajiyeva et al. (2018) studied the dynamics of surface wave propagation in a pre-stressed incompressible half-space when accompanied by both vertical and tangential loads. In this study, however, we extend the work of Khajiyeva et al. to include the presence of a coating layer above the half-space, upon which the loads are acted. Moreover, we prescribe sufficient perfect continuity conditions between the two layers, resulting in an inhomogeneous composite structure. Furthermore, related effective boundary conditions within the long-wave assumption are acquired for the model through the application of the asymptotic approximation method. Finally, approximate uncoupled pseudo-differential equations are derived on the surface, thereby admitting all the results of Khajiyeva et al. as limiting cases of concern.

This paper considers directions to devise methods for restoring the operational suitability of reinforced concrete structures. Mistakes of designers and non-compliance with the concreting technology of monolithic reinforced concrete structures lead to the formation of cracks and deflections of unacceptable size in reinforced concrete beams and floor slabs, as well as to insufficient strength of the elements. Such structures require not only an increase in bearing capacity but also the restoration of the operational suitability of damaged structures. A technique for restoring the serviceability of bendable reinforced concrete structures with increased deflections and excessive crack opening is proposed. To restore bendable reinforced concrete structures, surface reinforcement with pre-stressed fiber-reinforced plastics is suggested, which is ensured by the creation of a building lift in the damaged elements. Unlike conventional reinforcement methods, surface reinforcement techniques are characterized by high gain efficiency, corrosion resistance, low labor intensity, and short terms of work; they ensure strength increase and provide for economic feasibility. This study’s results established that the use of fiber-reinforced plastics not only increases the bearing capacity of reinforced concrete structures but also helps reduce the width of the cracks formed. Thus, it is possible to avoid an increase in the cross-section of structures and reduce the time of operations, which could lead to additional costs.

Copyright of Journal of Ordnance Equipment Engineering is the property of Chongqing University of Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Shrinkage and improper compaction of the repair layer are among the main reasons for the adhesion drop. Shrinkage results in cracking and improper compaction causes fine pores in the interface. Due to the fact that shrinkage and non-compacting are the main reasons for reducing strength and adhesion, therefore, in this paper, research has been done in this regard. The present study aimed to investigate the effect of polypropylene fibers on the shrinkage of mortars and bond of mortar/concrete interface. Moreover, the impact of diverse pre-stresses on the adhesion between mortar and concrete was evaluated by imposing prestresses on fiber-reinforced mortars. Adhesion was assessed by the “twist-off” and “pull-off” tests. Furthermore, the effect of fibers and pre-stress on the adhesion examined using SEM images and X-ray diffraction. It is necessary to assess the compressive strength of concrete and mortar in the field. Therefore, the aforementioned semi-destructive methods were employed to investigate the in-situ compressive strength of mortars at different ages. For this purpose, the correlation coefficient between the insitu and laboratory methods was defined and the scaling curves were plotted to convert the in-situ test results into compressive strengths of the mortars. The obtained findings indicated the positive effect of pre-stress on adhesion. In addition to their mechanical effect, the indirect effect of fibers on the chemical properties of the mortars reduces shrinkage and augments adhesion. Moreover, given the great relationship among the conclusion of “pull-off” and “twist-off” methods, the cost-efficient and available twist-off apparatus can be used for adhesion measurement instead of the costly and import pull-off apparatus. Adding 0.3% of polypropylene fibers to the mortars enhanced the bond strength by 76.8% and 41.7%, respectively and reduced the shrinkage of the mortars by 11%. An initial stress of 0.5 kg/cm2 increased the shear and tensile bond strength at the age of 90 days by 12.8% and 13.3%, respectively. [ABSTRACT FROM AUTHOR]

• Both time and frequency domain signals are input into the network. • A trainable weight coefficient is introduced for adaptive fusion. • Correlation between input UGW signal and predicted pre-stress is interpreted. Steel strands serve as the key load-bearing components of pre-stressed bridges, yet the identification of effective pre-stress for steel strands is a challenging task. In this study, a time and frequency adaptive fusion input-one dimensional convolutional neural network-long short-term memory (TFAFI-1DCNN-LSTM) framework was proposed for ultrasonic guided wave (UGW)-based effective pre-stress identification of steel strands. In this framework, the time and frequency domain signals of UGW were input into the network as two parallel branches, CNN and LSTM were utilized to extract spatial and serial-related features, and a trainable weight coefficient was introduced for adaptive fusion of time and frequency domain features. Firstly, ablation studies were conducted to investigate the influence of each key component in the proposed framework on the prediction results. Secondly, deep learning (DL) models of Res Net, Dense Net and Inception Net were introduced as comparisons, and the prediction results based on TFAFI-1DCNN-LSTM were compared with those based on the above DL models. Thirdly, the noise-robustness and performance under a few trainable samples of TFAFI-1DCNN-LSTM were also investigated. Finally, the outputs of various key layers of the proposed framework were subjected to dimensionality reduction and visualization to provide an intuitive demonstration of the feature extraction process, and the inherent mechanisms of the proposed framework were interpreted using local interpretable model-agnostic explanations (LIME). Results show that the architecture of TFAFI-1DCNN-LSTM is reasonably designed and all key components are necessary. The weights of features in time and frequency domain branches are rationally assigned due to the addition of an adaptive weight coefficient. Compared with other DL models, the proposed TFAFI-1DCNN-LSTM exhibits higher pre-stress identification accuracy, excellent noise-robustness, and superior performance under only a few trainable samples. The correlation between features extracted by the network and the pre-stress labels significantly increases with the deepening of the network, and the correlation between input UGW signals and predicted pre-stress values is effectively interpreted utilizing LIME, proving that the architecture of the proposed framework is reasonable and effective, the predicted results are reliable and credible. [ABSTRACT FROM AUTHOR]

• Enhanced stress condition for soft elastic perforated structure in linear elasticity. • Incorporating a small change in the normal to the boundary during deformation. • Predicting the influence of initial or residual stress in a perforated structure. • Large-deformation-based finite element simulations to verify accuracy. • Accurate referential analytic results for soft elastic structures and composites. Linear elasticity theory has been used extensively in the study of the elastic behavior of various perforated structures and composite materials requiring the accompaniment of appropriate boundary conditions to derive qualitatively correct and quantitatively referential solutions. When incorporating conventional boundary conditions, however, linear elasticity theory fails to predict certain essential phenomena associated with perforate structures and composite materials even when they undergo small deformations. For example, a soft elastic porous medium is appreciably stiffened when inflated despite the fact that the internal air pressure is significantly lower than the modulus of the medium itself. In this paper, we propose an improved stress boundary condition by simply incorporating a small change in the normal to the boundary during deformation. We show via numerical examples that in the context of linear elasticity theory, the use of this improved boundary condition offers the possibility of predicting the influence of initial or residual stress in a perforated structure on the elastic response of the structure to external loadings (which can never be captured with the use of conventional boundary conditions). We perform also large-deformation-based finite element simulations to verify the accuracy of the closed-form results obtained from the improved boundary condition for a soft elastic perforated structure with initial internal pressure. We believe that the idea presented in this paper will extend the applicability of linear elasticity theory and yield more accurate referential analytic results for soft elastic structures and composites. [ABSTRACT FROM AUTHOR]

This study examined the effect of an imposed equibiaxial pre-stress (EBPS) on the evaluation of mechanical properties, using the depth-sensing indentation method with a point-sharp indenter, through a numerical analysis of indentations simulated with the 3D finite element method. The predicted elastic modulus, E*, and yield stress, Y*, were used as elastic and plastic deformation resistances under the indentation, respectively. It was found that both increased nominally with the increase in compressive EBPS and decreased with the increase in tensile EBPS, even though the induced change in the piling-up or sinking-in around the indentations was not significant. The effect of EBPS on E* was described by the Hooke's law for an isotropic elastoplastic material, whereas that on Y* was accounted for by the change in the von Mises stress due to EBPS. [ABSTRACT FROM AUTHOR]

In order to study the pre-press transfer effect of bolt composite member, assume that the roadway surrounding rock is elastic foundation, take the roof as an example, the elastic foundation beam model of the roof which is supported by pre-stress bolt composite member was established. Based on the superposition principle, combining with boundary conditions, the deflection equation of the model was obtained. Combined with engineering examples, results show that deformation coordination coefficient β is an important parameter which affects the transmission of bolt pre-stress. The smaller β is helpful for the uniform transmission of bolt pre-stress. Increasing bending stiffness of the belt can deduce β and improve the effect of support. In the condition of different bolt arrangements, the distribution of roof counterforce is mainly influenced by end effect and superposition effect. The counterforce is higher at the end of the belt by the influence of end effect while higher at the middle of the belt by the influence of superposition effect. Optimal arrangement of bolt can be determined through the balance of end effect and superposition effect.

Pre-stressed ground anchor systems or tieback systems are commonly used at wide and irregular-shaped excavations, with the advantage of lower cost and ease of construction compared to the braced excavations, but they come with the drawback on permits for excavations near buildings and tunnels. Research on tieback systems in sands was generally conducted. However, the studies on the correlation between the retaining wall deflection and pre-stress force are few. The objectives of this paper are to study the influence of pre-stress force, depth of excavation, wall embedment length, and soil shear strength that is represented by soil friction angle on the deflection and soil pressure acting on the retaining wall. The parametric study was conducted on an excavation in sand using the finite element method with the Hardening soil model. The results showed that a 50 kN/m increase in pre-stress force reduced the wall deflection on top of the wall by 0.005–0.083% of excavation depth. However, the pre-stressing influence in reducing wall deflection at excavations became less significant along with the sand density increase due to higher friction angle contribution to excavation stability. Moreover, the pre-stress force needed for stabilization of the wall with long embedment length is smaller than those on the wall with shorter embedment length, since the embedment length increase of 0.25 times of excavation depth reduces wall top deflection by 0.002–0.095% of excavation depth. Also, the increase of soil density reduces the need for wall embedment length, so at dense sand, the embedment length of 0.5 times of excavation depth is sufficient to support the excavation.

The non-linear finite element simulation of the ASTM shear and pre-stressed compact tension tests was conducted. Tested specimens were cut from the glued laminated timber made of European spruce (Picea abies) with the lamina thickness of 10.5 mm and 45 mm. The 2D homogeneous orthotropic constitutive model of the tensile-shear fracture in timber, which has been proposed by the authors, was used. The model calibration was adopted from the authors' recent experimental study. The numerical results show that the model can adequately reproduce both the experimental response and the crack pattern, which in certain cases comprises of cracking parallel or perpendicular to fibers. Furthermore, the results confirm that the value of the parameter fASTM xy, obtained from ASTM shear test as the maximum attained force divided by the shearing area, represents the averaged stress at the failure plane, while the extreme stress experienced by the material is much higher. [ABSTRACT FROM AUTHOR]

Summary: The acoustic emission (AE) technique is a non‐destructive testing method widely used in various structural health monitoring fields, and it is highly sensitive to the emergence and development of material corrosion. This study developed a method of employing the AE technique to evaluate the corrosion degree of stay cable high‐strength steel wires under pre‐stress and impressed current cathodic protection (ICCP) in a simulated marine atmospheric rainwater environment. The variation characteristics of AE parameters under various pre‐stress levels and protection current densities were investigated. Results showed that the more negative the open circuit potentials (OCPs) and the greater the average corrosion rates, the higher the cumulative AE parameters. In the AE intensity analysis of corrosion damage for stay cable high‐strength steel wires, the constants J and the K were taken as 40 and 25 hits, respectively. The corrosion of steel wires was divided into no corrosion, slight corrosion, medium corrosion, and severe corrosion. The corrosion degree of specimens with ICCP was classified as no corrosion and slight corrosion, whereas that of unprotected specimens was classified as medium corrosion and severe corrosion. [ABSTRACT FROM AUTHOR]

In this paper, the effect of pre-stress condition on the resonance frequency of the transducer is studied by using numerical and analytical methods. To compare the obtained results, two sandwich-type transducers with nominal frequency of 25 kHz and 30 kHz are considered. Experimental determination of pre-stress value in transducer is described and measured. Then resonance frequency of transducers in the presence of pre-stress is determined by impedance analyser. Numerical analysis is conducted by modelling three-dimensional transducer in details at ABAQUS software. The resonance frequency is determined with and without pre-stress. The FE results show that by applying pre-stress on the transducers, the resonance frequency of transducers decreased. Furthermore, the FE results are very close to experimental results. Furthermore, a systematic analytical solution is presented based on one-dimensional wave propagation. The resultant displacement for each sub-section of the transducer is calculated and then all of them are assembled and solved by considering the continuity conditions of displacement and force components. It is found that pre-load condition that is produced by central bolt reduces resonance frequency of the transducer. The obtained analytical results provide fast and reliable model for predicting resonance frequency of transducer.

Micron-scale aluminum (Al) particles are plagued by incomplete combustion that inhibits their reactivity. One approach to improving reactivity is to anneal Al particles to increase dilatational (volumetric) strain which has also been linked to increased combustion performance. While optimal annealing temperatures have been identified (roughly 300 °C), little is known about cooling rate effects on particle combustion performance. This study examines the effect of quenching after annealing Al microparticles to 100, 200 and 300 °C on intra-particle dilatational strain and reactivity. Synchrotron X-ray diffraction analysis of the particles reveals the cooling rates in the range from 0.007 to 0.38 K/s have little effect on the dilatational strain of the aluminum-core, alumina-shell particles. The annealed and quenched Al particles were then combined with a metal oxidizer (copper oxide) to examine reactivity. Flame propagation experiments follow the same trend: flame speeds are unchanged until a critical annealing temperature of 300 °C is reached and performance is maintained for each annealing temperature regardless of cooling rate. These results show that altering the mechanical properties and combustion performance of Al particles is strongly dependent on the annealing temperature and unchanged with variation in cooling rate. The contributions from elastic and plastic deformation mechanisms on strain are also considered and additional experimental results are shown on the microstructure of an Al particle. Focused ion beam milling of an Al particle to electron transparency was combined with transmission electron microscope imaging in order to examine the microstructure of the Al particles. This confirmed that the Al microparticles have a polycrystalline structure shown by grains all exceeding 100 nm in size.

Micron-scale aluminum (Al) particles are plagued by incomplete combustion that inhibits their reactivity. One approach to improving reactivity is to anneal Al particles to increase dilatational (volumetric) strain which has also been linked to increased combustion performance. While optimal annealing temperatures have been identified (roughly 300 °C), little is known about cooling rate effects on particle combustion performance. This study examines the effect of quenching after annealing Al microparticles to 100, 200 and 300 °C on intra-particle dilatational strain and reactivity. Synchrotron X-ray diffraction analysis of the particles reveals the cooling rates in the range from 0.007 to 0.38 K/s have little effect on the dilatational strain of the aluminum-core, alumina-shell particles. The annealed and quenched Al particles were then combined with a metal oxidizer (copper oxide) to examine reactivity. Flame propagation experiments follow the same trend: flame speeds are unchanged until a critical annealing temperature of 300 °C is reached and performance is maintained for each annealing temperature regardless of cooling rate. These results show that altering the mechanical properties and combustion performance of Al particles is strongly dependent on the annealing temperature and unchanged with variation in cooling rate. The contributions from elastic and plastic deformation mechanisms on strain are also considered and additional experimental results are shown on the microstructure of an Al particle. Focused ion beam milling of an Al particle to electron transparency was combined with transmission electron microscope imaging in order to examine the microstructure of the Al particles. This confirmed that the Al microparticles have a polycrystalline structure shown by grains all exceeding 100 nm in size.

Copyright of Eastern-European Journal of Enterprise Technologies is the property of PC TECHNOLOGY CENTER and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Development of high-performance sandwich structures is particularly attractive for aerospace applications, where novel lighter materials and structures are object of extensive research. This work is focused on the design of a new high-performance Carbon FRP core as alternative to traditional periodic prismatic ones. The innovative core is designed as a 2D close-packing pattern of circular cells and manufactured by connecting pre-preg corrugated laminates in specific locations. The corrugated laminates are layered following an asymmetric sequence in order to generate residual thermal stresses within the core to enhance energy absorption and compressive properties. The distribution of the residual thermal stress within the core was numerically studied with a finite element model of the unit cell, in order to prove the positive contribution of the asymmetric layup on the mechanical properties and study the failure mechanisms of the unit-cell. Composite core samples were manufactured, and their mechanical properties were experimentally evaluated through compression, both out-of-plane and in-plane, and beam flexure tests. Results were compared in terms of specific properties with traditional aluminium honeycomb core, showing large increments of specific compressive strength (+84.6%), in-plane compressive modulus (over +500%), Specific Energy Absorption (+145%) and shear (>20%). The FEM model was validated against experimental compressive results, showing an error below 10%. The results show that the core is suitable for applications in novel high-performance sandwich structures, leading to numerous advantages in comparison to traditional cores, such as higher specific properties, manufacturability of complex sandwich structures and higher adhesion and compatibility with CFRP skins. [ABSTRACT FROM AUTHOR]

The present paper describes a novel experimental method for characterising the confined shear strength of concrete or rock‐like materials based on the use of pre‐stressed sample. This method, called PS‐PTS (Pre‐Stressed Punch‐Through‐Shear), employs a metallic confinement cell that is first quasi‐statically deformed so the concrete sample can be introduced in between the cell jaws. The confinement force is transmitted to the sample in the unloading stage. It is shown that this initial pre‐load level can be predicted by an elastic closed‐form solution. Strain‐gauges glued on the cell allow the confinement level applied to the sample to be experimentally measured during the pre‐stressing stage and the shear stage. In the next stage, the central part of the sample is subjected to a differential displacement towards the lateral parts by means of a hydraulic press so the confined shear strength of the tested material can be deduced. The results are compared to the data previously obtained with an "oedometric" confinement cell in terms of confinement stresses and shear strength. Highlights: A Pre‐Stressed Punch‐Through‐Shear technique is proposed based on pre‐loaded cell.A close‐form solution predicts the level of pre‐load applied to the sample.The cell is instrumented with strain gauges, so the applied forces are measured.The technique is applied to characterise the confined shear strength of concrete.Results are compared to those obtained with the 'Oedo‐PTS' testing method. [ABSTRACT FROM AUTHOR]

This paper considers directions to devise methods for restoring the operational suitability of reinforced concrete structures. Mistakes of designers and non-compliance with the concreting technology of monolithic reinforced concrete structures lead to the formation of cracks and deflections of unacceptable size in reinforced concrete beams and floor slabs, as well as to insufficient strength of the elements. Such structures require not only an increase in bearing capacity but also the restoration of the operational suitability of damaged structures. A technique for restoring the serviceability of bendable reinforced concrete structures with increased deflections and excessive crack opening is proposed. To restore bendable reinforced concrete structures, surface reinforcement with pre-stressed fiber-reinforced plastics is suggested, which is ensured by the creation of a building lift in the damaged elements. Fiberreinforced plastics have a high strain modulus, elastic nature of the diagram, and increased frost resistance; they tolerate fatigue effects well and are resistant to the effects of chemically active substances. Unlike conventional reinforcement methods, surface reinforcement techniques are characterized by high gain efficiency, corrosion resistance, low labor intensity, and short terms of work; they ensure strength increase and provide for economic feasibility. This study's results established that the use of fiber-reinforced plastics not only increases the bearing capacity of reinforced concrete structures but also helps reduce the width of the cracks formed. Thus, it is possible to avoid an increase in the cross-section of structures and reduce the time of operations, which could lead to additional costs. [ABSTRACT FROM AUTHOR]

Copyright of Engineering Mechanics / Gongcheng Lixue is the property of Engineering Mechanics Editorial Department and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

In this paper, the effect of bolt torque tightening has been investigated on the fatigue behavior of GLARE in double shear lap configuration. To do so, experimental fatigue tests were conducted using GLARE3-5/4-0.4 specimens with applied torques of 0 (finger tightened), 2 and 4 Nm at different cyclic longitudinal load ranges to achieve the stress-life (S-N) curves. The results revealed that applying and increasing the clamping force enhances the fatigue life of the GLARE specimens. Furthermore, comparison of fatigue test results of GLARE and available monolithic aluminum alloy 2024-T3 plates indicated when the applied load range is low, the effect of clamping force is more noticeable in GLARE specimens due to longer fatigue crack growth life of GLARE. Also, the occurrence of fretting fatigue didn't reduce the fatigue life of GLARE specimens considerably in contrary to aluminum sheets because of the laminated structure of GLARE. The obtained results can provide insights in designing bolted GLARE joints with superior fatigue in-service performance. [ABSTRACT FROM AUTHOR]

[Display omitted] • A new parameter α EL was proposed for pre-stress evaluation; • A theoretical model was established for UGW propagating in steel strand; • The α EL -based approach showed a higher measuring accuracy. Accurate prediction of the effective pre-stress in steel strands is of great importance for service performance assessment in pre-stressed structures. In this study, a new parameter for characterizing the pre-stress in steel strand is proposed, named energy leakage ratio (α EL) of ultrasonic guided wave (UGW). Firstly, the propagation of UGW between wires of the strand was theoretically analyzed. Then, finite element (FE) models of steel strand were established and laboratory experiments were conducted to verify the effectiveness and accuracy of the proposed α EL -based pre-stress evaluation approach. Results show that α EL increases linearly with inter-wire contact width. α EL can be taken as a new parameter for strand pre-stress identification, it shows a high linear correlation with pre-stress level, no matter whether the excitation position is located in core or helical wire. In terms of numerical and experimental results, the α EL -based pre-stress evaluation errors are within 3% and 4% respectively. Compared with the acoustoelastic effect based and nonlinear ultrasonic based approaches, the α EL -based approach showed the advantage in pre-stress identification accuracy. [ABSTRACT FROM AUTHOR]

Convection-enhanced delivery (CED) is a technique to bypass the blood-brain barrier and deliver therapeutic agents into the brain. However, animal studies and preliminary clinical trials have reported reduced efficacy to transport drugs in specific regions, attributed mainly to backflow, in which an annular zone is formed outside the catheter and the fluid preferentially flows toward the surface of the brain rather than through the tissue toward the targeted area. In this study, a finite element model of backflow was updated by implementing the pre-stress generated during needle insertion, which allows considering the effect of needle insertion velocity during CED infusions in agarose gel. The nonlinear mechanical properties of the agarose solutions were obtained by fitting experimental data from stress-relaxation tests. Additional experimental measurements of backflow lengths were used to adjust the pre-stress model. The developed model was able to reproduce changes of backflow length under different insertions velocities and flow rates. These findings reveal the relevance of considering the pre-stress in the tissue located around the needle surface during CED infusions into the brain. • A numerical model was developed to include the pre-stress during CED infusions. • In-vitro infusion experiments were performed to measure the backflow lengths. • Mechanical properties of agarose gel were obtained based on compression experiments. • The numerical model reproduced backflow lengths for different insertion velocities. [ABSTRACT FROM AUTHOR]

The inclusion of pre-stressed PET profiles as reinforcing fibers in structural elements is proposed. The PET-profiles are placed in a unidirectional and bidirectional fiber matrix with soft pre-tensioned condition that they could have advantages in structural members made of concrete in some precise applications, for instance, structural support for road safety barriers. A universal machine is used to test PET-profiles with different width, knots and even other conditions. The desired PET profile is chosen and the concrete mixture is designed under the ACI standard guidance. Pre-stressed PET-profiles are included in wood molds shaped in beam-type and subsequently flexural strength is estimated. Finally, experimental tests results are presented for PET-profiles as structural reinforcement of beams made of concrete under pure flexural. Finally, a probabilistic model is used to estimate the PET contribution in terms of exceedance of the rupture modulus.

Power transmission is generally carried out through electric cables supported by transmission pole (Utility pole) of various materials and cross sections. However, their utilization depends on climatic conditions and external loads acting on them. The forces comprise of wind pressure, tension in conductors and seismic vibrations due to earthquakes. These loads induce various stresses in the pole like bending, shear, crushing etc. There is a necessity for investigation of these stresses in the existing utility pole subjected to the loads acting on them. The objective of the paper is to study the stresses developed in the tapered rectangular utility pole made of Steel Reinforced Concrete material which is 8m in total length. The work includes the calculation of stresses in the existing poles made of three grades of concrete (namely M40, M45, and M50), four different load cases of pre stressing (zero or no pre-stress, with a pre-stress of 50%, 60%, and 75% of maximum allowable strength of steel reinforcement), under the effect of 185 kmph wind velocity. Theoretical and FEA of stresses were carried out and the results were compared. The 3D solid modelling of pole is carried out using SOLIDWORKS and imported into ANSYS 15.0 for calculation of stresses. It is observed that in either cases of RCC and PSCC, the stresses developed in the concrete cause failure of the pole. However, in case of PSCC, the stresses causing failure are less compared to RCC and may have longer life.

In this paper, the effect of pre-stress condition on the resonance frequency of the transducer is studied by using numerical and analytical methods. To compare the obtained results, two sandwich-type transducers with nominal frequency of 25 kHz and 30 kHz are considered. Experimental determination of pre-stress value in transducer is described and measured. Then resonance frequency of transducers in the presence of pre-stress is determined by impedance analyser. Numerical analysis is conducted by modelling three-dimensional transducer in details at ABAQUS software. The resonance frequency is determined with and without pre-stress. The FE results show that by applying pre-stress on the transducers, the resonance frequency of transducers decreased. Furthermore, the FE results are very close to experimental results. Furthermore, a systematic analytical solution is presented based on one-dimensional wave propagation. The resultant displacement for each sub-section of the transducer is calculated and then all of them are assembled and solved by considering the continuity conditions of displacement and force components. It is found that pre-load condition that is produced by central bolt reduces resonance frequency of the transducer. The obtained analytical results provide fast and reliable model for predicting resonance frequency of transducer. [ABSTRACT FROM AUTHOR]

A thin linear elastic strip is clamped at both ends and subjected to a linear stress distribution across its width. We use Kirchhoff beam theory to study this problem. If displacements out of the strips own plane are prohibited, the straight configuration remains stable as long as the compression is not too high. With the three‐dimensional spatial description of the rod theory, we find possible buckling modes even in the case of average tensile stresses in the beam. Comparison with shell and beam finite elements shows excellent agreement with the analytical investigation, also with respect to the supercritical behavior. [ABSTRACT FROM AUTHOR]

Machining-induced residual stress plays a significant role in the corrosion resistance and fatigue life of the manufacturing end product. In the current study, milling experiments were performed to investigate the influence of pre-stress on the surface residual stresses. For this purpose, finite element (FE) simulations of the orthogonal cutting based on arbitrary Lagrangian-Eulerian approach were performed. To validate the simulation results, a device was designed to stretch the workpiece with pre-stresses before the machining process. The residual stresses obtained under different pre-stresses were measured based on the varied bending deflection of the workpiece after each material layer removal. As a result, the general variation trend of residual stress profiles that obtained under different pre-stresses was found well consistent with the finite element simulation results, indicating that the proposed residual stress measuring principle is reliable. Furthermore, the pre-stress loaded on the Ti6Al4V part can significantly affect the distribution of machining-induced residual stresses, implying that surface residual stresses can be adjusted by employing appropriate values of pre-stresses during the machining process. [ABSTRACT FROM AUTHOR]

The interest of aerospace and automotive fields in the improvement of energy absorption properties of composite materials has stimulated researchers to design new typologies of cores of sandwich-structures under impact events. In this work, a sandwich structure based on pre-stressed bistable carbon fibre composite core is proposed. The core, named Circular Prestressed Carbon Core (CPCC), takes advantage of the asymmetric fibres orientation and the bistability-concept to enhance energy dissipation and reduce the damage extension during impacts. The impact campaign was conducted both experimentally and numerically to analyse the mechanical properties of the core and to study the contribution of the residual stresses. Experimental results were compared with an aerospace-grade aluminium honeycomb-core and a not-prestressed version of the core. Results proved its unique impact characteristics, showing, an improvement of the maximum-force up to 171 % and 23 % in comparison with aluminium honeycomb and not-prestressed CPCC, respectively. The specific properties of the CPCC were considerably higher than the aluminium sandwich, with peak force values up to +75 %, displacement reduced up to −71 %, and non-destructive evaluation (NDE) test showed a reduction of the projected damaged area by ∼20 %. These results demonstrates that the CPCC structure constitutes a novel high-performance sandwich core for improved impact resistance. [ABSTRACT FROM AUTHOR]