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Featured Application: This paper details the development and proof of concept testing for a novel apparatus capable of testing brittle materials in multiaxial tensile states, allowing the development of more robust failure models. Aging infrastructure is increasingly costing taxpayers due to increased repair and replacement costs. Ultra-high performance concrete (UHPC) has recently been recognized as a viable material for both the repair of concrete and steel infrastructure as well as a replacement material for new structures due to its enhanced mechanical and durability properties. Such uses require a much better understanding of the multiaxial tensile properties of UHPC to utilize the material more efficiently. This study focused on developing a novel apparatus capable of subjecting specimens to tensile forces in each of the three principal directions simultaneously. Such an apparatus could collect data for a portion of the failure surface that currently only has a small dataset to establish trends. The "Looney Bin" was designed to test 50-mm cube specimens in triaxial tension, biaxial tension, tension-compression, and tension-tension-compression stress states. Once the apparatus and fixtures were designed and fabricated, trial tests were conducted on a non-proprietary UHPC without steel fibers to establish a test method for each of the stress states evaluated. Data were then collected for different stress states using the established procedures and plotted against previously published failure models for UHPC to verify that the collected data were reasonable. [ABSTRACT FROM AUTHOR]

Aging infrastructure is increasingly costing taxpayers due to increased repair and replacement costs. Ultra-high performance concrete (UHPC) has recently been recognized as a viable material for both the repair of concrete and steel infrastructure as well as a replacement material for new structures due to its enhanced mechanical and durability properties. Such uses require a much better understanding of the multiaxial tensile properties of UHPC to utilize the material more efficiently. This study focused on developing a novel apparatus capable of subjecting specimens to tensile forces in each of the three principal directions simultaneously. Such an apparatus could collect data for a portion of the failure surface that currently only has a small dataset to establish trends. The “Looney Bin” was designed to test 50-mm cube specimens in triaxial tension, biaxial tension, tension-compression, and tension-tension-compression stress states. Once the apparatus and fixtures were designed and fabricated, trial tests were conducted on a non-proprietary UHPC without steel fibers to establish a test method for each of the stress states evaluated. Data were then collected for different stress states using the established procedures and plotted against previously published failure models for UHPC to verify that the collected data were reasonable.

Abstract The low cycle fatigue strength properties of the additively manufactured Ti-6Al-4V alloy are experimentally investigated under proportional and nonproportional multiaxial loading. The fatigue tests were conducted using hollow cylinder specimens with and without heat treatments, at room temperature in air. Two fatigue tests were conducted: one for proportional loading and one for nonproportional loading. The proportional loading was represented by a push-pull strain path (PP) and the nonproportional loading by a circle strain path (CI). The failure lives of the additively manufactured specimens were clearly reduced drastically by internal voids and defects. However, the sizes of the defects were measured, and the defects were found not to cause a reduction in fatigue strength above a critical size. The fracture surface was observed using scanning electron microscopy to investigate the fracture mechanisms of the additively manufactured specimens under the two types of strain paths. Different fracture patterns were recognized for each strain paths; however, both showed retention of the crack propagation, despite the presence of numerous defects, probably because of the interaction of the defects. The crack propagation properties of the materials with numerous defects under nonproportional multiaxial loading were clarified to increase the reliability of the additively manufactured components.

Based on the damage ratio strength theory, a dimensionless damage ratio strength criterion for fiber-reinforced concrete (FRC) under true triaxial stress states was established under the assumption of small strains. Based on the experimental data of steel fiber–reinforced concrete (SFRC), polypropylene fiber–reinforced concrete (PFRC), hybrid fiber–reinforced concrete (HFRC), and steel fiber–reinforced high-performance lightweight concrete (SFRHLC), parameters for the damage ratio criterion were recommended. The damage ratio values were verified by SFRC experimental results under uniaxial, biaxial, and triaxial loading conditions, and the damage ratio values of SFRC under uniaxial tension, uniaxial compression, and biaxial equal compression stress conditions were compared with those of plain concrete. The true triaxial damage ratio strength criterion can be reduced to the conventional triaxial criterion and biaxial criterion, and the corresponding simplified strength criteria were proposed. The proposed dimensionless six-parameter criterion agrees well with the experimental results of the aforementioned materials for true triaxial, conventional triaxial, and biaxial loading conditions. Compared with the strength criteria in other studies, the proposed criterion can accurately represent the strength characteristics of FRC. [ABSTRACT FROM AUTHOR]

This paper presents an experimental investigation of the failure behavior of SiC fiber-reinforced SiC matrix (SiC/SiC) composite tubes under multiaxial loading. A new testing apparatus is designed to independently apply axial stress and internal pressure to SiC/SiC tubes. Acoustic emission (AE) is used to monitor the damage growth in the specimen. Based on the measured stress–strain response, a strain-based criterion is proposed to determine the proportional limit stress (PLS). The proposed strain-based criterion is compared with the PLS determined by the AE measurement. The PLS is determined for different loading ratios to form a multiaxial failure surface. By testing multiple replicates, the statistical variations of the PLS are determined. Based on the experimental results, a mathematical model is developed to characterize the probability distribution of the PLS of SiC/SiC composites under multiaxial loading. [ABSTRACT FROM AUTHOR]

The low cycle fatigue strength properties of the additively manufactured Ti-6Al-4V alloy are experimentally investigated under proportional and nonproportional multiaxial loading. The fatigue tests were conducted using hollow cylinder specimens with and without heat treatments, at room temperature in air. Two fatigue tests were conducted: one for proportional loading and one for nonproportional loading. The proportional loading was represented by a push-pull strain path (PP) and the nonproportional loading by a circle strain path (CI). The failure lives of the additively manufactured specimens were clearly reduced drastically by internal voids and defects. However, the sizes of the defects were measured, and the defects were found not to cause a reduction in fatigue strength above a critical size. The fracture surface was observed using scanning electron microscopy to investigate the fracture mechanisms of the additively manufactured specimens under the two types of strain paths. Different fracture patterns were recognized for each strain paths; however, both showed retention of the crack propagation, despite the presence of numerous defects, probably because of the interaction of the defects. The crack propagation properties of the materials with numerous defects under nonproportional multiaxial loading were clarified to increase the reliability of the additively manufactured components. [ABSTRACT FROM AUTHOR]

Abstract Carburized gears are widely used in geared machines such as wind turbines. Contact fatigue problems occur in engineering practice, reducing reliabilities of machines. Contact fatigue failures are related to many factors, such as gradients of mechanical properties of the hardening layer. In this work, an elastic-plastic contact model of a carburized gear is developed based on the finite element method to evaluate contact fatigue failure risk, considering variations in hardness and strength. The Dang Van multiaxial equivalent stress is calculated via Python coding within the Abaqus framework. The gradient of yield strength along the depth from case to core is considered. The concept of local material fatigue failure risk is defined to evaluate the probability of pitting failure. The effects of design factors, such as the case hardening depth (CHD), surface hardness, and contact pressure on fatigue failure risk, are studied. As the CHD increases or the surface hardness decreases, the risk of deep spalling failure reduces. The increase in surface hardness leads to a decreased risk of pitting failure, while the variation in CHD hardly affects the pitting failure risk.

Low-frequency vibrations are common as background noise in urban and industrial environments. They originate from natural or artificial sources: road vehicles, industrial machinery, wind, etc., and constitute a ubiquitous energy source. In the framework of energy harvesting, magnetostrictive materials are an attractive alternative solution to the brittleness and geometrical limitations of piezoelectric materials. While numerous previous works dealt with uniaxial stress on selected materials, the exploration of the effects of multiaxial loadings and material anisotropy has not yet been investigated as a way to improve the performance of low-frequency vibration energy harvesting systems. In this work, we investigated the capability of grain-oriented electrical steel in an energy-harvesting context. This material has been selected as a model material, notably as it is abundant and cost-effective. It shows limited magnetostriction but significant elastic, magnetic, and magnetostrictive anisotropy. We combined experimental and predictive simulation results to discuss the possibility of increasing the levels of harvested energy by playing with the orientation of magnetic and mechanical stimuli. Various orientations of magnetic field and mechanical stress were considered with regard to the rolling direction of the material. Unexpectedly high energy density amounts, up to 10 mJ·cm−3, were obtained, competing with giant magnetostrictive materials like Terfenol-D or Galfenol. [Display omitted] • A multiaxial model was used to predict the energy harvested from Ericsson cycle. • The highest the coupling (stress and field angle), the highest the harvested energy. • For GO FeSi, compressive stress close to yield stress, H along RD is ideal. • 13.1 mJ·cm−3 was predicted to be the maximum level of energy potentially available. [ABSTRACT FROM AUTHOR]

This paper presents a stress and fatigue life analysis for the shaft of a 100 hydro-generator. Normal and shear stresses were measured at the cylindrical section of the shaft at several power levels. A finite element model was developed to find points with stress concentration and the corresponding stress concentration factor. Analytical models taken from the literature were implemented to calculate stresses during phase-to-ground and phase-to-phase failure. Stresses were linked with the generation history of the machine taken each hour during one year to obtain the stress history. With the stress history, the Wang-Brown multiaxial fatigue model and the Miner’s rule were used to estimate the fatigue life. Stresses on the shaft were found to be dependent on the generated power. Operation at partial load (between 30 and 60% of full load) was found to produce higher vibration in comparison with operation at power greater than 60% of full load. Changing the power level produced higher damage than the vibration produced during operation at a steady state condition. It was found that the shaft has a practically infinite life even when the damage produced during electrical failure was considered.

This paper deals with the creep characteristics of the aircraft turbine disc material of nickel-base superalloy GH4169 under high temperature. From the perspective of continuum damage mechanics, a new creep life prediction model is proposed to predict the creep life of metallic materials under both uniaxial and multiaxial stress states. The creep test data of GH4169 under different loading conditions are used to demonstrate the proposed model. Moreover, from the perspective of numerical simulation, the test data with analysis results obtained by using the finite element analysis based on Graham creep model is carried out for comparison. The results show that numerical analysis results are in good agreement with experimental data. By incorporating the numerical analysis and continuum damage mechanics, it provides an effective way to accurately describe the creep damage process of GH4169. [ABSTRACT FROM AUTHOR]

Carburized gears are widely used in geared machines such as wind turbines. Contact fatigue problems occur in engineering practice, reducing reliabilities of machines. Contact fatigue failures are related to many factors, such as gradients of mechanical properties of the hardening layer. In this work, an elastic-plastic contact model of a carburized gear is developed based on the finite element method to evaluate contact fatigue failure risk, considering variations in hardness and strength. The Dang Van multiaxial equivalent stress is calculated via Python coding within the Abaqus framework. The gradient of yield strength along the depth from case to core is considered. The concept of local material fatigue failure risk is defined to evaluate the probability of pitting failure. The effects of design factors, such as the case hardening depth (CHD), surface hardness, and contact pressure on fatigue failure risk, are studied. As the CHD increases or the surface hardness decreases, the risk of deep spalling failure reduces. The increase in surface hardness leads to a decreased risk of pitting failure, while the variation in CHD hardly affects the pitting failure risk. [ABSTRACT FROM AUTHOR]

This paper presents a fatigue life calculation for the pole, the rotor rim, and the rotor spoke of a 100 MW hydro-generator. Mechanical and electrical parameters during unit start, with the hydro-generator working at several power levels, and during a load rejection from 100 MW were measured. The measured loads together with centrifugal force, gravity, and magnetic pulling force were included in finite element models to quantify stresses. Also, stresses produced during over-speed, phase-to-ground failure, and phase-to-phase failure were evaluated. A stress history for each element was obtained by fitting the calculated stresses, with the power generation history collected hourly during one year of operation of the machine. Fatigue life calculation was performed by using the stress history along with the Wang-Brown multiaxial fatigue model.

An accurate life prediction is important to the design of a high-speed rotary blade subjected to multilevel cyclic loads. The widely used Miner's rule and uniaxial stress prediction method always deviate from actual life of the blade. A prediction method based on Chaboche's nonlinear damage evolution model is utilized to predict the multilevel cyclic fatigue life of a compressor blade subjected to start-up centrifugal force and working aerodynamic force. Chaboche's model is verified by comparing with experimental data of different materials. The blade life predicted by Chaboche's rule and Miner's rule are compared, and it is found that Miner's rule might overestimate the blade life under the typical loading spectrum of start-up centrifugal force and working aerodynamic force. To study the impact of multiaxial stress state on the blade life, the life predicted by uniaxial stress method is compared to that predicted by multiaxial stress method, and it demonstrates that the multiaxial stress state of the blade should not be neglected. Finally, the crack propagation of the blade under multiaxial fatigue loads is simulated successfully by element deletion technique, which is conducted by translating Chaboche's multiaxial model into a user defined UMAT program in ABAQUS. The predicted crack propagation life is compared with that predicted by an approximate Paris law method plate model. This research proves that the method to predict the blade life subjected to multilevel cyclic loads based on multiaxial Chaboche's model could provide a valuable reference for engineering blade fatigue design. [ABSTRACT FROM AUTHOR]

Giant magnetostrictive materials such as Terfenol-D and Galfenol are used to design actuators and sensors, converting magnetic input into a mechanical response, or conversely, mechanical input into a magnetic signal. Under standard operating conditions, these materials are subjected to stress. It is therefore important to be able to measure, understand and describe their magneto-mechanical behaviour under stress. In this paper, a comprehensive characterisation of the anhysteretic magneto-mechanical behaviour of Terfenol-D was performed. An energy-based multiscale approach was applied to model this behaviour. Finally, it was shown that the strain behaviour of Terfenol-D can be satisfactorily described using an analytical model derived from the full multiscale approach.

Composite bolted joints are quite necessary for composite structures connection, which has become the main limit for the use of composites in main load-bearing structures. In this article, a fatigue model of composite bolted joint based on equivalent stress is established by programming in ABAQUS USDFLD subroutine to simulate the progressive failure of composite bolted joints. By introducing three-dimensional Tsai–Hill static failure criterion, equivalent stress is calculated for investigating effects of multiaxial stress on fatigue life. In the subroutine of progressive failure for fatigue model, fatigue life of composite bolted joint and damage state of elements that are meshed in the process of modelling are connected by defining field variable. Different fatigue modes are predicted here by changing stress amplitude and ratio loading, in which simulation results agree well with that obtained in corresponding experiments. [ABSTRACT FROM AUTHOR]

The polymeric materials in general exhibit strong time-temperature dependence and viscoelastic behavior. The time-temperature superposition principle is typically used to estimate the long-term viscoelastic behavior. In addition, Mises criterion and Tresca criterion have been proposed to estimate the yield or failure stresses in a multiaxial stress state and Christensen failure criterion can be applied in the case of different tensile and compressive strengths. In this study, using molecular dynamics method, uniaxial and biaxial tensile and compression test simulations were performed for polypropylene at various strain rates and temperatures. It was observed that the compressive fracture stresses were higher than the tensile fracture stresses. In addition, the fracture stress was high at a low temperature and high strain rate and these fracture stresses are in good agreement with Christensen failure criterion curves. Furthermore, the long-term viscoelastic behavior can almost be predicted from the short-term viscoelastic behaviors at three different temperatures using time-temperature superposition principle. But, the simulations at a wide range of temperatures is important to predict the more accurate long-term viscoelastic behavior. [ABSTRACT FROM AUTHOR]

A detailed design of a new rotational single sheet tester device which allows comprehensive multiaxial magneto-mechanical analysis of ferromagnetic sheets is proposed. The challenges that arose during the mechanical and magnetic design phases are addressed. The applicability of the device is tested by performing magneto-mechanical measurements on an M400-50A electrical steel sheet. Results under several multiaxial magneto-mechanical loadings with circular and alternating magnetic flux densities are reported. It is shown that the effect of multiaxial stress on iron losses can be much more significant than that of uniaxial stress. [ABSTRACT FROM AUTHOR]

Abstract Adhesively bonded joints are becoming widespread in the composites industry and therefore there is a need for quantitative information on the mechanical strength of the material used. The great strength and stiffness of a composites structure may be strongly undermined by their weakest part, the bonded joint. Unfortunately, the testing of adhesives in bulk form may not be representative of their behaviour in a layered state, typically quite thin, because of differences in the polymerization process and lack of adhesive-adherend interfaces. The drawback of the test in thin layer is the stress concentration at the edges, typical in the single lap or t-peel joints, and also the chance of having the adhesive subjected both to a shear and predominant peel stress. This work deals with the characterization of adhesives in thin film under uniform distributions of multi-axial stresses, which is the typical application condition. The test exploits a tubular butt-bonded specimen, previously investigated by the authors, which guarantees a non-singular stress field over the adhesive layer both in shear and normal directions. According to the analytical prediction, in addition to the direct normal stress, both radial and circumferential secondary stresses arise in the adhesive, due to the constrained lateral contraction imposed by the adherends (Poisson's effect). The test campaign investigates two chemically different, commercial adhesives, an acrylic and an epoxy resin. By means of a biaxial testing machine, we applied to the specimens eight different combinations of normal and shear loads ranging from pure tensile to a shear-compressive stress state. As expected, both the pure shear stress and the compressive stresses lead to better performances of the adhesive layer with respect to tensile loading. The authors compare a variety of failure criteria from the literature and propose a simple multiaxial criterion to obtain a failure envelop of the experimental data. The applicability of the criterion is also assessed on experimental tests found in literature on different configurations and gives fairly good results. The outcome of study is a simple stress based, failure criterion, which can be used to predict the failure of several adhesive bonded joints, relying only on monoaxial experimental data. [ABSTRACT FROM AUTHOR]

Highlights • A new model was proposed to reasonably predict creep life. • The notch weakening effect was found in the brazed joint. • The creep life increases with notch angle increases while it decreases with notch radius increases. • The brazed joint under multiaxial stress was mainly fractured by intergranular brittle mode. Abstract The brazed components operating at high temperature inevitably suffer from multiaxial creep under multiaxial stress. In this study, the creep strain, fracture and failure mechanisms of HastelloyC276-BNi2 brazed joint under multiaxial stress were studied by experiment and finite element modeling (FEM). A new damage evolution model was put forward to estimate the creep fracture behavior of brazed joint under multiaxial stress. And the influences of notch angle and radius were also discussed. The notch weakening effect was exhibited in the brazed joints. The creep life is not only dependent on the creep fracture strain but also on notch type. The proposed creep damage evolution model can reasonably reflect the relationship between creep fracture ductility and multiaxiality. The predicted creep life by proposed model agrees very well with the experimental results. Most importantly, the fracture mechanisms of brazed joint under multiaxial stress were revealed and the creep damage evolution was well interpreted by FEM. Graphical abstract Image, graphical abstract [ABSTRACT FROM AUTHOR]

• A reduced order model is proposed to efficiently predict creep-fatigue behavior. • Damage variable is reconstructed by orthogonal interpolation functions. • The reduction elements selected by damage rate are more reasonable. • An increase in the reduction elements can improve the accuracy of the ROM. This paper devises an efficient reduced-order model based on a unified viscoplastic constitutive model for predicting creep–fatigue behavior under multiaxial loading. In the preprocessing stage, the first cycle is numerically simulated using the unified viscoplastic constitutive model, and all element damage variables are recorded as representative variable snapshots. The orthogonal basis of damage is extracted by proper orthogonal decomposition and used as the interpolation function. The reduction elements are selected by minimizing the interpolation functions and damage variable samples. When predicting the subsequent cycles, the unified viscoplastic constitutive model is only applied to the selected reduction elements to evaluate the local damage, and the damage of the remaining elements is directly reconstructed using interpolation functions. In this manner, the computational cost of the constitutive equation is significantly decreased. Two reduction element selection strategies based on the damage rate and the damage are compared, which reveals that the extrapolation ability of the damage rate is more reasonable than that of damage. The feasibility of the devised model is validated through a comparison with the results of multiaxial loading tests. This demonstrates that the model accurately describes the creep–fatigue damage evolution while enhancing the computational efficiency. [ABSTRACT FROM AUTHOR]

This study discusses fatigue properties of low carbon steel, type SS400 steel, under non-proportional loading. Multiaxial fatigue tests under proportional and non-proportional loading conditions with various stress amplitudes were carried out using a hollow cylinder specimen at room temperature. In the test, three types of stress paths were employed. They are a push-pull, a reversed torsion and a circle loading. The circle loading is a cyclic loading combined the push-pull and the reversed torsion loading in which axial and shear stress waveforms have 90 degrees phase differences. From the obtained test results, poor evaluations of failure life under non-proportional loading are indicated when the life is correlated by the equivalent strain range based on von Mises Δεeq and the non-proportional strain range ΔεNP. A modified strain parameter is presented which can evaluate the failure life in high and low strain levels under non-proportional loading

The paper contains the results of fatigue tests of smooth and notched specimens made of 10HNAP (S355J2G1W) subjected to proportional cyclic loading with use of mean values stress. The results obtained for specimens under bending, torsion and one combination of bending with torsion for four mean values have been compared. The experimental data have been collected in the tables and shown in the figures with use of various σa(τa)-N fatigue characteristics for which parameters of the regression equations have been determined. The influence of average values on the allowable stress amplitudes and amplitude of moments at the level close to the fatigue limit depending on the angle α determining loading combination and the average stress is also shown. The greatest effect of the notch on fatigue life compared to smooth specimens is observed at symmetrical loads. At unsymmetrical loads with non-zero mean stress, this effect clearly weakens or disappears.

In this paper, we derived a new piezoresistance tensor equation for a cubic single crystal. This equation can be expressed in terms of the three independent principal components of piezoresistance tensors, the isotropic and deviatoric stress tensors, and the fourth-rank coordinate transformation tensor. The piezoresistance tensor equation can be decomposed into a relation between only the hydrostatic part of the stress tensor and the trace of the resistivity change tensor and into a relation between only the deviatoric parts. The hydrostatic part of the piezoresistance tensor equation is invariant with respect to a coordinate transformation. On the other hand, the deviatoric part of the tensor equation is traceless. The proposed piezoresistance tensor decomposition gives a new physical insight into the classical theory of Pfann and Thurston [J. Appl. Phys. 32 (2008) 1961]. It was shown that Pfann and Thurston's theory can be rewritten as a special case of our tensor decomposition. Furthermore, to demonstrate the consistency between the proposed tensor equation and the experimental evidence, some basic experiments on a single-crystal silicon piezoresistive rosette stress gauge subjected to multiaxial stress were carried out. [ABSTRACT FROM AUTHOR]

Initial ovality is an inevitable problem in the process of pipe bends manufacturing which results in the stress redistribution of the pipe bends working at high temperature. In order to study the influence of ovality on creep life of pipe bends, full-size creep experiment of P92 pipe bend subjected to in-plane bending has been conducted. The creep strains and outside diameters of dangerous positions have been measured. The microstructures of three different positions of the pipe bend were compared through SEM and the results showed the number and size of the carbide precipitation were the largest at the flank of the pipe bend, which indicated that the creep damage developed fastest at the flank. The modified Kachanov--Robatnov constitutive equations were used to stimulate the creep of P92 pipe bends with FEA software. The representative stress, damage and multiaxiality distributions of the pipe bends have been discussed. The FEA results were consistent with the experimental results and the influence of initial ovality on creep life of P92 pipe bends were analyzed. The results showed that creep life of pipe bends reduced by the increase of ovality and their relationship coincided with the parabolic law. [ABSTRACT FROM AUTHOR]

This paper examines the anisotropic and rate-dependent mechanical behavior of a rolled AZ31B magnesium alloy under multiaxial loading over a wide range of strain rates ranging from 10 − 4 to 10 5 s − 1 . It is shown that stress state, strain rate as well as loading orientation collectively influence the plastic flow. The rate dependence of the plastic flow in the material varies with the loading orientation. The texture-induced anisotropy, however, changes very little with the strain rate. The microstructures of the as-received and deformed specimens suggest that detailed analysis of initial spread in textures is necessary, especially under multiaxial stress states. The failure mechanisms are also observed to evolve with loading rate. Our results provide useful insights into the deformation and failure mechanisms in magnesium and extend the understanding of the mechanical properties of magnesium to the ultra-high strain rate regime ( 10 5 s − 1 ). [ABSTRACT FROM AUTHOR]

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Abstract: This paper discusses low cycle fatigue, creep and creep‐fatigue life evaluation methods for a SUS 304 austenitic stainless steel in a full range of strain and stress multiaxiality using a cruciform and cubic specimen. Five multiaxial strain parameters are investigated whether or not they appropriately express the trend of low cycle fatigue lives in the full range of biaxial stress state. Then, the effects of the stress biaxiality and triaxiality on creep void formation are discussed. The stress biaxiality and triaxiality raise the creep void formation and the void formation is confirmed even in an equi‐triaxial tension creep test in which the value of von Mises equivalent stress is zero. However, the stress biaxiality slightly shortens creep rupture lifetimes but the stress triaxiality drastically reduces creep rupture lifetimes. Finally, the effect of strain biaxiality on creep‐fatigue life is discussed based on the experimental results using a cruciform specimen by applying the linear damage rule. The predicted results of creep‐fatigue lives under biaxial strain states are slightly dependent on the applied multiaxial strain and stress parameters but there is no significant difference in the predicted lives depending on the multiaxial strain and stress parameters. [ABSTRACT FROM AUTHOR]

Biaxial and triaxial compression tests were performed on 100 × 100 ×100 mm cubic specimens of concrete under different stress loading rates. All the tests were performed using a true triaxial testing machine. The analysis of the data revealed that the intermediate principal stress, hydrostatic stress and shear stress are the main factors influencing the failure criterion for concrete under multiaxial stress. Based on the twin shear strength theory, three failure criterion models were developed. The five-parameter model A considers the shear strength as the main factor, the five-parameter model B considers hydrostatic strength as the main factor, and the six-parameter model considers both the shear strength and hydrostatic strength. The parameters for these failure criterion models have clear physical significance and form the failure criterion in a theoretical analysis. Models A and B apply to different stress states and show similar results. The six-parameter model can apply to most stress states, but the computed results depend on the boundary conditions. This convenient model can also be extended for nonlinear analyses of concrete under multiaxial stress in compression. [ABSTRACT FROM AUTHOR]

It is well known that the Alkali-Silica Reaction (ASR) expansion in concrete is influenced by the stress state of the material. However, the extent and nature of this influence is not completely understood due to the scarcity of experimental investigation under triaxial stress states. This paper presents experimental ASR expansion curves obtained from cubical concrete specimens subjected to three different triaxial stress states, by means of a new testing machine especially designed for this purpose. The results seem to confirm that the volumetric ASR expansion rate is reduced as the applied volumetric compressive stress is increased. Additionally, there seems to be an increase of the expansion rate in the less compressed direction in detriment of the expansion rates in the most compressed ones. [ABSTRACT FROM AUTHOR]

This article presents a modified Neuber’s rule to estimate the inelastic stress and strain at the toe of welded plate connections under large-scale cyclic yielding, caused by the low-cycle fatigue loadings. In contrast to the original Neuber’s rule, which usually overestimates the notch-tip elastic–plastic stress and strain as the applied nominal stress approaches or exceeds the material yield strength, the modified Neuber’s rule provides a convenient and accurate estimation of the stress and strain at the weld toe as an alternative to the time-consuming numerical computation. The numerical study covers the variations in both the geometric configuration and the material properties in the modified Neuber’s rule. This article also provides closed-form expressions for the two critical parameters in the modified Neuber’s rule to facilitate engineering applications. [ABSTRACT FROM AUTHOR]

• Optimized notch acuity ratios can correspond to the notch stress state accurately. • The relationship of notch acuity ratios to skeletal point positions was established. • The predictions of the creep rupture life are in good agreement with the experiment. • The relationship between the void growth rate and the stress triaxiality is revealed. In this paper, a unified creep rupture life prediction method based on continuum damage mechanics under multiaxial stress was proposed. By optimizing the traditional skeletal point stress method, the number of models that need to be computed during the simulation was reduced by 5/6, and the generality of the method for different notch sizes was significantly improved. Creep tests on Ni-based superalloy round bar specimens with different notch sizes, which verify the accuracy of the method, were conducted. Furthermore, creep rupture mechanism analyses were conducted for different notch sizes by combining finite element simulations with experiments, stress and damage were analyzed, and void growth was explained based on triaxial stress states. [ABSTRACT FROM AUTHOR]

The paper reports on the results of a comparison involving mathematical models applied for fatigue life calculations where the mean load value is taken into account. Several models based on the critical plane approach and energy density parameter were tested and analyzed. A fatigue test results for three types of materials are presented in this paper. The specimens were subjected to bending, torsion and a combination of bending with torsion with mean value of the load. Analysis of the calculation results show that the best fatigue life estimations are obtained by using models that are sensitive to the changes of material behavior under fatigue loading in relation to the specified number of cycles of the load.

A simplified multiscale approach and a Helmholtz free energy based approach for modeling the magneto-mechanical behavior of electrical steel sheets are compared. The models are identified from uniaxial magneto-mechanical measurements of two different electrical steel sheets which show different magneto-elastic behavior. Comparison with the available measurement data of the materials shows that both models successfully model the magneto-mechanical behavior of one of the studied materials, whereas for the second material only the Helmholtz free energy based approach is successful. [ABSTRACT FROM AUTHOR]

The abilities of a simplified multiscale and a Helmholtz energy HE models models from the literature to predict the multiaxial stress dependent magnetic hysteresis behavior of electrical steel sheets are analyzed. The identification of the models is performed using only uniaxial magneto-mechanical measurements. Reasonable accuracy between the measurements and the modeled results is obtained. With this paper, the applicability of the HE-based model for predicting the multiaxial magneto-mechanical behavior of electrical steel sheets is verified for the first time. The differences between the studied models and possible modifications to increase the accuracy of them are discussed. Some brief guidelines for the applications are given. [ABSTRACT FROM AUTHOR]

The presented work is based on experiments determining the strength of sewing seams in car seat covers. In order to understand the behavior of the seam on the car seat, it is necessary to create the conditions that will be close to real stresses. This experiment has been carried out on a designed device that simulates multiaxial stress. In this study, four different sizes of spun polyester and polyamide threads are used to sew the textile material (used for car seat cover) by a lockstitch sewing machine. By using the device made for measuring the multiaxial strain the average load of seam strength were obtained. After the experiments a theoretical calculation of the stress by finite element method (FEM) is follow. The carried models were drawn in Creo parametric and FEM analysis has been conducted in the software ANSYS. Based on the measurements of the individual components (strength of the material, threads in the loop. . .) and entire assembly has been compiled to make a numerical model. [ABSTRACT FROM AUTHOR]

Biaxial, triaxial and uniaxial tension creep tests were performed using 304 stainless steel using biaxial and triaxial creep machines, and creep void formation and creep rupture lifetimes were observed. Raised creep void formation was found in biaxial and triaxial stress states than in uniaxial stress state. Clear void formation was confirmed under the equi-triaxial stress state, which demonstrated that von Mises equivalent stress was not essentially a suitable measure to evaluate creep damage and rupture lifetime in multiaxial stress states. A new equivalent stress taking account of the stress multiaxiality was proposed based on the multiaxial creep rupture data obtained in this study. [ABSTRACT FROM AUTHOR]

To evaluate fatigue life of composite laminate with hole under random loading, a random fatigue life prediction model is established by hybrid time-frequency domain method in this paper. Firstly, dynamic response of composite laminate is obtained from FE model in frequency domain. Secondly, root mean square of stress of six stress components of critical damage point in frequency domain are transferred to stresses in time domain. At last, 3D Tsai–Hill static failure criterion is adopted to convert the multiaxial stress into the uniaxial equivalent stress. Fatigue life is predicted by equivalent stress fatigue life code. The method is validated with the random vibration fatigue test of carbon fibre-reinforced composite laminate. Numerical results are compared with random fatigue experiments which show good agreement with numerical results. [ABSTRACT FROM PUBLISHER]

Many concrete structures around the world are experiencing expansion of concrete due to alkali-silica reaction (ASR). ASR expansion is reduced in the direction of compressive stress and is transferred to the unstressed directions. However, the relationship between ASR expansion and a multiaxial stress state in concrete, which is often the case in concrete structures, is inadequately understood. This paper presents a relationship between ASR expansion and the stress state of concrete based on experimentally determined triaxial expansions of unstressed and uniaxially, biaxially, and triaxially stressed concrete cube specimens. The expansion-stress relationship is not coupled with reaction kinetics and is isolated from the effect of creep and shrinkage by subtracting the deformations measured on non-reactive control specimens. The proposed relationship was implemented in a finite element program to predict the measured expansion values on concrete cube specimens. The predicted expansions are in reasonable agreement with the measured expansions. [ABSTRACT FROM AUTHOR]

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X-ray diffraction techniques have been developed to measure flow stresses of polycrystalline sheet metal specimens subjected to large plastic deformation. The uncertainty in the measured stress based on this technique has not been quantified previously owing to the lack of an appropriate method. In this article, the propagation of four selected elements of experimental error is studied on the basis of the elasto-viscoplastic self-consistent modeling framework: (1) the counting statistics error; (2) the range of tilting angles in use; (3) the use of a finite number of tilting angles; and (4) the incomplete measurement of diffraction elastic constants. Uncertainties propagated to the diffraction stress are estimated by conducting virtual experiments based on the Monte Carlo method demonstrated for a rolled interstitial-free steel sheet. A systematic report on the quantitative uncertainty is provided. It is also demonstrated that the results of the Monte Carlo virtual experiments can be used to find an optimal number of tilting angles and diffraction elastic constant measurements to use without loss of quality. [ABSTRACT FROM AUTHOR]