Tension-compression Loading Research Articles

Numerical study of bilinear isotropic & kinematic elastic–plastic response under cyclic loading

The study of elastic–plastic response of metals and alloys subjected to cyclic loads has several applications with phenomenon such as Baushinger effect, ratcheting, elastic and plastic shakedown having been reported in numerous studies. With the use of finite element analysis (FEA) being increasingly popular for study of mechanical components exhibiting elastic–plastic behaviour, the validation of results from plasticity analysis is an onerous task. Hence, this paper attempts to study the low-cycle elastic–plastic response during a uniaxial tension–compression loading regime using FEA. The stress–strain relationships due to controlled loading with bilinear isotropic (BISO) and kinematic hardening (BKIN) behaviour are studied. It has been observed that while kinematic hardening has a consistent stress–strain hysteresis loop with no accumulation of plastic strain during cyclic loading, isotropic hardening has shown accumulation of stress at constant strain cycles, but no accumulation of total strain at constant stress cycles. When maintaining constant total strain on the specimen for isotropic hardening, it has been observed that while the elastic strain increases, the plastic strain decreases with the number of cycles. FE simulations with different strain and stress factors were performed and the variations of peak stresses and strains were documented.

The Influence Of Age On The Recovery From Worksite Resistance Exercise In Firefighters

Worksite resistance training may reduce injuries and improve performance in firefighters, however aging may prolong the recovery process. PURPOSE: This study examined the influence of age on recovery following an acute bout of worksite resistance training. METHODS: Nineteen young and 19 older career firefighters (FFs) completed an acute bout of resistance exercise in addition to pre- and post-testing 24, 48, and 72 hours post-exercise. A work-related fatigue (WRF) survey was completed to assess daily fluctuations in work demands. Ultrasonography was used to assess cross-sectional area (CSA) and echo intensity (EI) of the vastus lateralis, in addition to muscle thickness (MT) and EI of the biceps brachii. To determine maximal jump height and associated velocity, participants completed 3-4 countermovement jumps while standing on a jump mat with a linear transducer attached at the waist. Upper-body peak force (PF) was measured during an isometric upright row task, using a calibrated tension-compression load cell. Lower body PF was examined with the participants seated in a custom-built, calibrated isometric dynamometer and their right knee flexed at 60 degrees. Following 3 submaximal warm-up contractions, participants performed 3 maximal voluntary contractions for each strength assessment lasting 3-4 s. The FFs completed the circuit-style resistance exercise bout following pre-testing, which included 3 sets of 8-10 repetitions at 80% of their predicted 1-repetition maximum of the deadlift, shoulder press, lunge, and upright row. Linear mixed models, controlling for WRF, were used to analyze all primary outcomes, with subject as the random effect and group and time as fixed effects. Alpha level was set a priori at 0.05. RESULTS: There was a significant group by time interaction effect for WRF (P=0.002) and was controlled for in subsequent analyses. There were no other significant group by time interactions (P>0.171). Collapsed across time, young FFs showed greater lower body PF (P=0.006), jump performance (P<0.024), and lower VL EI (P=0.008) values. Across time points, upper-body PF (P=0.023) and jump performance (P<0.029) decreased as muscle size increased (P<0.006) for both groups. CONCLUSION: These results indicate that age may not influence the recovery from a bout of worksite resistance exercise in FFs.

Damage evolution of tuff under cyclic tension–compression loading based on 3D digital image correlation

We have investigated the damage evolution and crack propagation of tuff rocks under axially cyclic tension–compression (T–C) loading with different amplitudes. The field of axial strains in the rock surface was obtained by three-dimensional digital image correlation (3D-DIC) method. The apparent strains were used to analyze the damage evolution along with the nucleation and propagation of microcracks until rock failure. The experimental results demonstrated that a local damage zone (LDZ) was formed when the loading amplitude exceeded a certain value, and the rock sample was prone to tensile failure under T–C cyclic loading. Based on arrangement of the virtual extensometers on the field of axial strains, the axial stress–strain curves, maximum axial strain, secant moduli, and dissipated energy evolution were obtained as a function of cycle number. It was observed that the variations in these mechanical parameters and dissipated energy significantly increased in the T–C cycle test with the increase in the loading amplitude. Particularly, due to obvious accumulation of residual compressive strain during the first cycle, the maximum tension stress increased, secant modulus decreased, and the dissipated energy evidently increased under tension during the second cycle. Furthermore, the mechanical parameters and dissipated energy evolution as a function of cycle number inside and outside the LDZ under 80% amplitude confirmed that the deformation mainly occurred inside the LDZ and the energy mainly dissipated for the nucleation and propagation of tensile microcracks vertical to the loading direction inside the LDZ during rock failure process.

On the comprehensive stability analysis of axially loaded bistable and tristable metastructures

Approaches to systematic analysis of essentially nonlinear structures with multistable responses, controlled buckling and snapping behavior have received much attention recently in the context of mechanical metamaterials design. A snapping bistable element is generally a highly efficient damper, performing well even at very low forcing frequencies. In this paper, we transfer basic tools of the metamaterials analysis to macroscopic systems relevant to civil and mechanical engineering applications. Such systems are comprised of only several bistable elements. Followed by analysis of a single snapping bistable axial (two-force) element, we consider a combination of two elements with antisymmetric properties and demonstrate a robust tristable performance of the resultant structure in low-frequency or quasistatic tension-compression loading cycles. The tristability provides an overall response that is symmetric for tension and compression, which makes it interesting for applications in machinery and large-scale seismic structures.

Structural relaxation in amorphous materials under cyclic tension-compression loading

The process of structural relaxation in disordered solids subjected to repeated tension-compression loading is studied using molecular dynamics simulations. The binary glass is prepared by rapid cooling well below the glass transition temperature and then periodically strained at constant volume. We find that the amorphous system is relocated to progressively lower potential energy states during hundreds of cycles, and the energy levels become deeper upon approaching critical strain amplitude from below. The decrease in potential energy is associated with collective nonaffine rearrangements of atoms, and their rescaled probability distribution becomes independent of the cycle number at sufficiently large time intervals. It is also shown that yielding during startup shear deformation occurs at larger values of the stress overshoot in samples that were cyclically loaded at higher strain amplitudes. These results might be useful for mechanical processing of amorphous alloys in order to reduce their energy and increase chemical resistivity and resistance to crystallization.

Estimation of equivalent stresses and equivalents of the fatigue test programs of airframe composite elements

It is known that for metal components of aircraft structures, stress is one of the most important parameters used to assess the fatigue damage resistance of a structural element for a given program of its fatigue tests. The method and the procedure for estimating the values of this parameter for metal elements of aircraft structures are presented It is noted that for aircraft structural elements made of polymer composite materials, neither the concept of the stress parameter nor the methods for calculating estimates of the values of this parameter are currently defined in domestic and foreign studies of the fatigue strength of such elements. In order to achieve particular progress in the considered area, the definition of the stress parameter of fatigue test programs for composite aircraft structural elements is proposed. For the case of uniaxial tension-compression load of laminates from layered composites representing the upper and lower panels of composite wings of transport category aircraft, a method for calculating the estimation of this parameter is proposed. It is shown that using the stress parameter, the following main tasks can be solved: assessment of the damage resistance of a structural element with a given program of its fatigue tests; comparison of damages resistance of various programs, calculation of equivalents between the programs; calculation of fatigue life of layered composites samples and elements using the fatigue curve under regular load. It is noted that the fundamental meaning of the proposed method for calculating the equivalent stresses and equivalents of fatigue test programs is the use of a special hypothesis of a fatigue damage accumulation rule. An example of calculating the equivalent stresses and equivalents of various modifications of the quasi-random program for CFRP T300/5208 [45/0/-45/90] 2s samples of fiber-carbon composite with the open hole is presented. The fatigue life of these samples under load with the considered modifications was calculated using the obtained values of equivalent stresses and equivalents. Good agreement between the calculated results and experimental data is shown.

Extremely - low cycle fatigue fracture of Q235 steel at different stress triaxialities

This study presents an experimental and numerical investigation on the Extremely-Low Cycle Fatigue (ELCF) behavior of Q235 structural steel under different stress states and large strain amplitudes. A set of Q235 structural steel cylindrical specimens of different radii of curvature were selected to examine the effect of the triaxial state of stress on the fracture behavior. Cyclic axial tension-compression loading tests characterized by large strain amplitudes were conducted to obtain the hysteresis loops and the failure process by measuring both macroscopic and microscopic fracture morphologies. The results shows that, the failure behavior of Q235 steel in ELCF loading is a mixture of fatigue fracture and ductile fracture. Specimens with different stress triaxialities are characterized by different failure modes. A fracture criterion, namely the Combinatory Work Density Model (CWDM), was calibrated based on the test results. Furthermore, a cyclic plasticity constitutive model, i.e., the Chaboche model, was calibrated to describe the yield and cyclic hardening behaviors of the Q235 structural steel. Finite element (FE) simulations in the commercial software ABAQUS accounting the calibrated CWDM and Chaboche model were carried out to evaluate the fracture characteristics with different stress triaxialities and their stress-strain hysteretic curves under ELCF loading. The simulation results demonstrate that the developed FE model can reproduce the hysteretic characteristics and capture the failure process of Q235 structural steel. The proposed practical numerical tool can be used for the ELCF failure prediction in steel structures under complex stress state.

Fluid-solid coupling numerical simulation on ideal porous structure of rat alveolar bone

Fluid shear stress (FSS) caused by interstitial fluid flow within trabecular bone cavities under mechanical loading is the key factor of stimulating biological response of bone cells. Therefore, to investigate the FSS distribution within cancellous bone is important for understanding the transduction process of mechanical forces within alveolar bone and the regulatory mechanism at cell level during tooth development and orthodontics. In the present study, the orthodontic tooth movement experiment on rats was first performed. Finite element model of tooth-periodontal ligament-alveolar bone based on micro computed tomography (micro-CT) images was established and the strain field in alveolar bone was analyzed. An ideal model was constructed mimicking the porous structure of actual rat alveolar bone. Fluid flow in bone was predicted by using fluid-solid coupling numerical simulation. Dynamic occlusal loading with orthodontic tension loading or compression loading was applied on the ideal model. The results showed that FSS on the surface of the trabeculae along occlusal direction was higher than that along perpendicular to occlusal direction, and orthodontic force has little effect on FSS within alveolar bone. This study suggests that the orientation of occlusal loading can be changed clinically by adjusting the shape of occlusal surface, then FSS with different level could be produced on trabecular surface, which further activates the biological response of bone cells and finally regulates the remodeling of alveolar bone.

Analysis of the ageing effect on the cyclic tension–compression loading behaviour of bitumen and mastics

Within the bituminous mixture the binder is subjected to different stress-state modes but the cyclic loading response is usually characterized on shear mode. This research investigates the evolution with ageing of the undamaged linear rheological behaviour and resistance to cyclic loading of bituminous materials using a tension–compression strain-sweep test. The results show that, similarly to the shear mode response, mineral fillers may induce a greater stiffening effect than ageing treatment, although the comparative evolution with ageing of materials may differ from that based on the shear mode response. The damage progression rate increases faster at lower temperatures and for the stiffer materials (mastics), where the flow deformation contribution to crack formation is smaller. The testing temperature is determinant for the evaluation of the effect of ageing and filler on fatigue resistance.

Analysis of the Bauschinger Effect in Cold Drawn Pearlitic Steels

Prestressing steel wires usually undergo cyclic loading in service. Therefore, it is of interest to analyse certain features of their mechanical behaviour under this type of loading, such as the Bauschinger effect (BE) or the hardening rule, that fit the real mechanical behaviour appropriately. In this study, different samples of high strength pearlitic steel wires were subjected to cyclic tension-compression load exceeding the material yield strength, thus generating plastic strains. From the experimental results, various parameters were obtained revealing that analysed steels exhibited the so-called Masing type BE. In addition, the variation of the BE characteristics (of the effective and internal stresses) with the applied plastic pre-strain indicated that the studied materials followed a mixed strain hardening rule with the domination of the kinematic component.

Experimental low cycle fatigue testing of circular bars with radial through-holes subjected to tension-compression loading

Experimental low cycle fatigue testing of circular bars with radial through-holes subjected to tension-compression loading

Development of a mini-tensile approach for sheet metal testing using Digital Image Correlation

The miniature uniaxial tensile testing is a simple yet powerful method to characterise the behaviour of a material. Based on this technique, an experimental system was developed aiming the determination of sheet metal mechanical properties, using the Digital Image Correlation (DIC) technique. A tensile-compression loading device was designed with a maximum load capacity of 2.5 kN. The device includes custom-made clamps that guarantee the alignment of the sample with respect to the loading axis. To evaluate the aptitude of miniature samples and the use of Digital Image Correlation (DIC) in this type of scale, some tensile tests were performed using different types of miniaturised geometries and the results were compared with a macro specimen reference. Additionaly, some cyclic tests were also performed, in order to evaluate the possibilities of developed prototype on the tensioncompression loading paths.

A general energy based fatigue failure criterion for the carbon epoxy composites

A normalized energy-based fatigue failure criterion, which employs off-axis stress and strain components to compute strain energy during cyclic loading, is presented in the current research. The new model is capable of predicting the fatigue life of unidirectional laminates subjected to tension-tension, compression-compression and tension-compression loading in any arbitrary fiber orientation. Furthermore, the proposed model is used to predict the fatigue life of multidirectional composite laminates under different cyclic loading conditions, including various stress ratios. The model is validated by the experimental data of unidirectional, cross-ply, angle-ply and multidirectional carbon/epoxy composite laminates taken from the literature. In the unidirectional and multidirectional laminates effect of fiber orientation and stress ratio are diminished, respectively. The suggested fatigue model is capable of predicting the fatigue life of angle-ply and cross-ply laminates using limited experimental data. Nonetheless, it does not result in good accuracy for multidirectional laminates with arbitrary lay-up sequence under compression-dominant loadings.

Experimental Fatigue Life Investigation on a Standard PMMA Compact Tension Specimen Equipped by the Lock Technique

The lock technique is a method to decrease crack growth by putting a lock on the crack which the focus of this study is to experimentally characterize the influence of the lock technique on crack growth behavior and life assessment. In this study, polymethyl-methacrylate rectangular standard compact tension plates were used as the test samples. Three different edge crack and lock configurations were tested for total six samples in order to assess fatigue life and fracture resistance, and experiments were conducted using a high-frequency fatigue test machine that applies cyclic tension–compression loads to the samples. In this study, effects of varying lock and hole geometry on crack initiation and propagations are investigated. Detecting of the crack initiation life and assessing crack propagation life from crack initiation until fracture moment are investigated. The experimental results show that the crack growth life is reduced in the lockless standard cracked specimen compared to the locked samples, and similarly, fracture strength in specimens equipped with the lock is more in comparison with the lockless specimens.

A new approach to finite element modelling of cyclic thermomechanical stress-strain responses

Modern finite element based structural analyses of thermomechanically loaded structures require accurate simulations with low computational times. However, increasing the complexity of material models capable of modelling cyclic phenomena of engineering materials usually also increases the computational time. Here we present the implementation of the Prandtl operator approach into a finite element solver as a new material model for the study of the stress-strain response of solids subjected to thermomechanical loading. The main advantage of this model is its high computational speed, due mainly to the implicit consideration of the Masing and memory rules by variable temperatures, either during a single load cycle or during a complex thermomechanical load history. The model enables temperature-dependent elastoplastic stress-strain modelling using the von Mises yield function, associated flow rule and multilinear kinematic hardening. The commonly used elastic predictor–plastic corrector procedure now contains an improvement in the calculation of the equivalent plastic strain increment. This includes modelling of the true stress by the time-efficient temperature-dependent spring-slider model. The second advantage of the approach is a reduced number of material parameters per temperature required by the Ramberg–Osgood-type description of the cyclic curve. These material parameters can be obtained from either uniaxial strain controlled low cycle fatigue tests or uniaxial incremental step tests. The model has been validated on several load cases of both a thermomechanically loaded single finite element under tension-compression and shear loads, and a cantilever beam subjected to bending loads. Comparisons with reference material models show almost identical behaviour of the new and the Besseling model, but with the advantage of having up to 35 percent shorter computation times.

Application of Principal Component Analysis (PCA) for the Choice of Parameters of a Micromechanical Model

The main objective of this work is to apply the Principal Component Analysis (PCA) to the key parameters of a micromechanical model, namely the shape parameter of inclusion (grain) (ratio =a/b) and γ viscoplastic parameter in view of a better simulation. In this work, the sensitivity of the model to parameters and γ is evaluated on the stabilized global stress during cyclic Tension-Compression (TC) loadings and out-of-phase Tension–Torsion, with a sinusoidal waveform and a phase lag of 90 between the two sinusoidal signals TT90 loadings. Indeed several values ​​of and γ are pulled thanks to these loading, we use later the PCA in order to choose the couple (, γ) adequate to launch our simulation. The model used is expressed as part of the self-consistent approach and time-dependent plasticity. Based on the Eshelby tensor, this model considers that the elastic behavior is compressible. For a polycrystalline structure, the grains are deformed by crystallographic sliding located in the most favorably oriented systems and which support a strong constrained stress . Keywords: PCA, grain shape , viscoplastic parameter γ, Self-consistent model, Non-incremental interaction law, Elasto-inelastic. TC and TT90 loading

Influence of loading parameters in cyclic tension-compression regime on crack-bridging behaviour of PVA microfibres embedded in cement-based matrix

The mechanical performance of fibre-reinforced cement-based materials may considerably vary depending on the particular loading scenario. The article at hand investigates the effect of the loading parameters in cyclic tension-compression regime on bridging behaviour of aligned short PVA microfibres in cement-based matrix. Under such loading, microfibres suffer damages between crack flanks, and their bridging capacity decreases. To understand the damage processes in conjunction with the degradation of fibre bridging capacity, cyclic fibre pull-out tests were performed with subsequent damage analysis of the fibre. The influence of the cyclic regime on the bridging behaviour of single PVA microfibres was comprehensively studied. The results clearly showed a reduction of bridging capacity with an increase in the number of cycles and in the compression level in a reversed tension-compression loading regime. Based on these findings a damage quantification approach is suggested.

Investigation of mechanical properties, formability, and anisotropy of dual phase Mg–7Li–1Zn

In this article, the mechanical properties, microstructure, forming limit diagram (FLD) and anisotropy of dual phase Mg-7Li–1Zn alloy have been evaluated by a uniaxial tensile test at three directions, scanning electron microscopy (SEM), optical microscopy (OM) and hemispherical punch test at ambient temperature. The optical microscopy images showed that the microstructure of as-cast LZ71 alloy possesses a dual phase microstructure such as β-Li matrix with body-centered cubic (BCC) structure and a partitioned α-Mg phase with hexagonal closest packed (HCP) structure in lath shape. After rolling process, the α-Mg phase has been elongated and arranged in the rolling direction and anisotropy at different directions increased, but after full annealing, microstructure arranged more uniform and changed from elongated to the uniform structure which this is the factor that reflects the reduction of anisotropy. FLD shows the limiting surface strains that sheet metal can endure before the start of localized necking and fracture at different deformation modes in tension-tension and tension-compression loading paths. The FLD of Mg–7Li–1Zn showed that this material has desirable formability due to the BCC structure with high slip system in the ambient temperature. Also, the results of the tensile test matched with the obtained FLD. Results of SEM revealed many dimples and some flat and cleavage planes. They showed the combination of ductile and brittle fracture, but the ductile fracture is the dominant fracture mechanisms for Mg–7Li–1Zn. In summary, in the dual phase, Mg–Li alloys via controlling the weight percent of lithium and other alloying elements can be achieved the desired mechanical properties and used for various applications.

Enhancement of Fatigue Endurance by Al-Si Coating in Hot-Stamping Boron Steel Sheet

Most structural components undertake cyclic loads in engineering and failures always cause catastrophic economic losses and casualties. In the present work, the phase evolution of Al-Si coating of high-strength boron steel during hot stamping was investigated. Two types of 1500 MPa grade boron steel sheets, one with Al-Si coating and the other without, were studied to reveal the effect on the high-cycle fatigue behavior. The as-received continuously hot-dip Al-Si coating was composed of α(Al), eutectic Al-Si and τ5. After hot stamping at 1193 K, three phases formed in this coating: β2, Fe(Al,Si)2 and α(Fe). The experimental results showed that the endurance limit of the coated steel sheet was 370 MPa under 107 fully reversed tension-compression loading cycles as opposed to 305 MPa in the uncoated sheet. Both the coated and the uncoated specimens showed surface-induced transgranular fatigue fractures. In the uncoated sheet, the fatigue cracks were generated from the decarburization surface, but the Al-Si coating effectively prevented the occurrence of near-surface decarburization during high-temperature hot stamping, and the only cracks in the coated steel sheet were initiated at wire-cutting surfaces.

Verification of stress-intensity factor and compliance relations for a single edge notch specimen under tension-compression loading

Stress-intensity factor and compliance solutions developed for a single edge notch (SEN) specimen has been validated and verified for tension-compression loading. Fatigue crack growth tests were conducted on the SEN and a surface-crack specimen at stress ratios, R of −1.0 and −2.0 using IN718 forged nickel base superalloy material. (The surface-crack specimen is referred to as the KB-bar specimen in the literature.) Experimentally determined compliance values for the SEN specimen compared well with the analytically predicted values. In addition, crack lengths measured using the compliance equation compared well with crack lengths measured using potential drop and optical techniques. Finally, agreement was found between the SEN and KB specimens in the intermediate crack growth rate range.