Tension-compression Loading Research Articles

Natural Frequency and Modes of the Longitudinal and Torsional Vibrations in the Bars with Variable Cross Section

The paper is focused on the problem of natural frequencies and modes determination based on perturbation theory for longitudinal and torsional vibrations in bars with variable cross section. The mechanical properties and cross section geometry of the bar are changing small from the average value with regard to longitudinal coordinate. Based on the theory of small perturbations the analytical solution is obtained for natural frequencies and modes of the stationary harmonic vibrations in bars. The efficiency of the proposed method is supported by comparison and good agreement of the obtain results with a sharp solution for a given cross section profiles. It was established that the approximate solution is working good up to the ratio 2.5–3 between maximum and minimum diameter of cross section. The results of numerical simulations are aimed to estimate the geometry and elastic behavior of the metallic specimens for very high cycle fatigue experimental investigation under axial tension-compression and torsion loadings. The piezoelectric fatigue testing system and procedure is based on stationary vibration excitation in the metallic specimen at the first mode natural frequency.

General Reference and Design S–N Curves Obtained for 1.2709 Tool Steel

At present, due to advanced fatigue calculation models, it is becoming more crucial to find a reliable source for design S-N curves, especially in the case of new 3D-printed materials. Such obtained steel components are becoming very popular and are often used for important parts of dynamically loaded structures. One of the commonly used printing steels is EN 1.2709 tool steel, which has good strength properties and high abrasion resistance, and can be hardened. The research shows, however, that its fatigue strength may differ depending on the printing method, and may be characterized by a wide scatter of the fatigue life. This paper presents selected S-N curves for EN 1.2709 steel after printing with the selective laser melting method. The characteristics are compared, and conclusions are presented regarding the resistance of this material to fatigue loading, especially in the tension-compression state. A combined general mean reference and design fatigue curve is presented, which incorporates our own experimental results as well as those from the literature for the tension-compression loading state. The design curve may be implemented in the finite element method by engineers and scientists in order to calculate the fatigue life.

Molecular dynamics simulation of reinforcement mechanism of graphene/aluminum composites and microstructure evolution

Graphene/Aluminum (Gr/Al) composites with different graphene chirality and distribution patterns were established. The contribution of graphene interfaces to the mechanical properties of composites was investigated by using molecular dynamics methods. The composites strengthen about 10% of Young's modulus and 5% of tensile yield strength compared with aluminum. Influenced by the chiral structures of graphene, the fracture strain of zigzag composite is larger, and the yield stress of armchair composite is higher. Folding deformation of graphene promotes the yielding of the composites under compressive loading. Even if the graphene breaks, the graphene interface can effectively limit the dislocation motion, and the twins can only expand around the graphene. The results of both tensile and compressive tests showed that the uniform distribution of graphene was beneficial to enhance the mechanical properties of the composites. Graphene hinders the motion of pre-dislocations more than pinning dislocations. Therefore, the Bauschinger effect of composite is lower than that of pure aluminum under tension-compression loading.

Effect of loading type on fatigue property of specimens treated by cutting and rubbing process

Aiming for a result to improve fatigue strength, “cutting and rubbing process” which is a kind of surface treatment was used for forming a round-bar smooth-specimen, showing drastically enhanced rotating-bending fatigue strength. On the other hand, actual machine components and structures invariably contain geometrical irregularities, such as fillets, keyways, screw threads, and holes. Fatigue cracks initiated from such stress raisers, indicating that the validity of the cutting and rubbing process on fatigue strength of specimen with a stress raiser should be examined. In this study, fatigue tests of smooth and notched specimens finished by the cutting and rubbing process were conducted under some loading types including rotating-bending, tension-compression and torsion loading. Results showed that fatigue strength of notched specimens was significantly enhanced compared to that of smooth specimens under rotating-bending and tension-compression loads. In other words, the cutting and rubbing processing was more effective in stress raisers than the smooth surface. The physical background on the effect of loading type on the fatigue strength of the cutting and rubbing processed specimen was discussed based on the fracture origin, microstructure in the surface layer, stress gradient caused by both loading type and notch.

A numerical study on the effects of DP steel microstructure on the yield locus and the stress–strain response under strain path change

The mechanical response of dual phase (DP) steel exhibits a complex dependence on the microstructure. The chemical composition and microstructure characteristics of the phases have significant effects on the contrast between the response of the phases, which affects, not only the strength and ductility, but also the anisotropic response of DP steel under strain path changes. In this work, extended dislocation-based models of the ferrite and martensite phases of DP steel are proposed and used in a finite element based representative volume element approach to account for the contrast between the local response of the phases. The flow stress of each phase is computed as a function of the amount of substitutional and interstitial solute elements and the microstructural characteristics of the phase. Particular attention is paid to the phase model of the martensite phase. The model parameter controlling the storage of dislocations is related to the carbon content, which appears to be the most important parameter affecting the strength of martensite and its contrast with the local response of the ferrite phase. The model predicts a significant effect of the contrast between the local responses of the phases and the microstructure characteristics of each phase on the yield locus after prestraining and on the stress–strain behaviour after strain path change, i.e., forward-reverse shear loading and cyclic uniaxial tension–compression loading.

1 0 0] Dislocation core extension and decomposition in BCC bicrystal under biaxial loading

The evolution of grain boundary dislocation structure under biaxial tension–compression loading is simulated by the phase field crystal (PFC) method for small angle symmetric tilt grain boundary (STGB) of body center cubic (BCC) bi-crystal. Extension of the STGB dislocation core under the strain and the extended width of the core with the strain increasing are studied. In the elastic deformation process under the loading, the extension of the grain boundary dislocation core is accompanied by increasing the strain energy of the system. When the extension of the dislocation core reaches maximum critical width, the extended dislocation core occurs to decompose into three dislocation cores, in which two cores is in no-extended state, the Burgers vector direction of which is in the same direction of the original extended dislocation. The other dislocation core is of the extended type which Burgers vector direction is opposite to the Burgers vector direction of the original extended dislocation core. By establishing the macroscopic energy equation of the extended dislocation core system, it can be well revealed that the elastic strain energy is mainly stored in the extended dislocation defects and the complete lattice of the matrix. At the same time, it also reveals the function relationship between the energy of the extended dislocation core and the width of the extended dislocation during the biaxial loading process of the bi-crystal, as well as the critical condition of energy instability and the change of the energy barrier of the system for the dislocation extension core decomposition.

Plastic deformation of ultra-thin pure titanium sheet subject to tension-compression loadings

Measurement of the Bauschinger effect of ultra-thin metallic sheet by the conventional tension-compression (TC) test is challenging due to the premature buckling during compression. In this study, a test method based on a multi-layered sandwich specimen is newly introduced to suppress the buckling in the uniaxial compression. Theoretical calibration is conducted for obtaining accurate flow stress under compression by correcting the effects of adhesive and friction induced by supporting side plates. Also, strains during the TC tests are measured by the digital image correlation (DIC) technique. From the proposed TC test with the sandwich specimen, plastic deformation of 0.1-mm-thick ultra-thin pure titanium sheet was investigated under reverse loading. Finally, the constitutive model based on the distortional hardening concept is newly developed and calibrated to reproduce the Bauschinger effect of the investigated ultra-thin sheet subject to TC loadings.

An anomalous compression-induced softening behavior of AA6014-T4P during cyclic loading

This paper investigated the cyclic plasticity of AA6014-T4P with the tension-compression (T-C) and compression-tension (C-T) cyclic loading tests. A new compression-induced softening behavior is found and modeled. Specifically, the material was softened permanently during the tensile load when a compressive pre-strain was applied, whereas such an abnormal phenomenon was not observed when the loading sequence is reversed. Moreover, the magnitude of the permanent softening scale linearly with the compressive pre strain. Therefore, we term this phenomenon as compression-induced softening in this paper. Based on this compression-induced softening phenomena, a modified Y–U model is formulated by introducing a correction factor that modifies the hardening rate of the boundary surface to describe the permanent softening effect, which can predict the compression-induced softening well. Our work reveals a new phenomenon for the cyclic loading of metal sheets and stimulates further efforts on the path-dependence of metal plasticity.

Evidence supporting reversible martensitic transformation under cyclic loading on Fe–Mn–Si–Al alloys using in situ neutron diffraction

Fe–Mn–Si-based alloys, such as Fe–30Mn–4Si–2Al and Fe–15Mn–10Cr–8Ni–4Si (in mass%), show superior resistance to plastic fatigue compared to the conventional steels, which is ascribed to the reversible back-and-forth movement of {111}〈112¯〉γ Shockley partial dislocations associated with a reversible martensitic transformation between the face-centered cubic γ-austenite and hexagonal close-packed ε-martensite. The purpose of this study was to gather evidence of the reversible martensitic transformation using in situ neutron diffraction under cyclic loading. Three Fe–30Mn–Si–Al alloys with different Gibbs free energy differences at 298 K: Fe–30Mn–6Si (ΔGγ→ε = −250 J/mol), Fe–30Mn–5Si–1Al (ΔGγ→ε = −128 J/mol), and Fe–30Mn–4Si–2Al (ΔGγ→ε = −8.5 J/mol), were studied to unravel the effect of phase stability on the degree of reversibility. The reversible martensitic transformation between γ-austenite and ε-martensite during tension–compression loading is demonstrated as bulk-averaged insights in the Fe–30Mn–4Si–2Al alloy. The forward γ → ε transformation was induced by tensile loading, and the formed ε plates were reversed to γ during unloading and subsequent compressive loading. Furthermore, successive compressive loading induced a different variant of the ε plates from the variant formed under tensile loading, which also reverted to γ by subsequent tensile loading. Such repetition of the γ ↔ ε transformation in the Fe–30Mn-4Si–2Al alloy is thought to increase the plastic fatigue life compared to the Fe–30Mn–6Si and Fe–30Mn–Si–1Al alloys, in which the γ ↔ ε transformation is rarely reversible. Herein, we discuss the mechanism of the deformation-induced reverse transformation and propose an optimum thermodynamic condition: a negative close-to-zero ΔGγ→ε.

Machine learning for extending capability of mechanical characterization to improve springback prediction of a quenching and partitioning steel

Quenching and partitioning (QP) steels exhibit apparent tension-compression asymmetry and evolving Bauschinger effect as plastic deformation proceeds, which brings challenges to accurately predict springback of QP steel parts. Loading-reverse loading tests are conducted to characterize the Bauschinger effect of a QP steel with a strength grade of 1500 MPa (QP1500), where the maximum achievable strains are limited. A machine-learning method is developed to extend the capability limit of physical tension-compression (TC) or compression-tension (CT) tests and virtually generate stress vs. strain curves at larger strains (up to 0.18), which cover the strain history of an actual forming part (e.g. M-shaped part). Then a data-driven method is proposed to calibrate parameters of a kinematic hardening model (Yoshida-Uemori model), which adopts all TC and CT stress vs. strain curves from physical tests and machine learning. This new set of Yoshida-Uemori model parameters is used in finite element simulations to predict springback of an M-shaped QP1500 steel part, and an obviously improved agreement is reached between simulation and experimental measurements of the M-shaped part. The mean error of predicted local springback distance was reduced to 0.23 mm. It is demonstrated that machine learning method is capable to capture the asymmetric and evolving Bauschinger effect within a much broader strain range and improve springback prediction of QP1500 steel. • QP1500 steel exhibits evolving Bauschinger effect as a function of strain. • QP1500 steel shows obvious tension-compression asymmetry between TC & CT loading. • Machine learning (ML) is employed to acquire TC/CT curves at larger strains. • A data-driven calibration method for YU parameters uses data from experiment & ML. • Data-driven calibration enhances springback prediction of QP1500 steel part.

Numerical and Analytical Studies of Low Cycle Fatigue Behavior of 316 LN Austenitic Stainless Steel

Abstract Mechanical components are frequently subjected to severe cyclic pressure and/or temperature loadings. Therefore, numerical and analytical low cycle fatigue methods become widely used in the field of engineering to estimate the design fatigue lives. The primary aim of this work is to evaluate the accuracy of the most commonly used numerical and analytical low cycle fatigue life methods for specimens made of 316 LN austenitic stainless steel and subjected to fully reversed uniaxial tension–compression loading, in the room temperature condition. It was found that both maximum shear strain and Brown–Miller criterions result in a very conservative estimation for uniaxially loaded specimens. However, maximum shear strain criteria provide better results compared to the Brown–Miller criteria. The total strain energy density approach was also used, and both the Masing and non-Masing analysis were adopted in this study. It is found that the Masing model provides conservative fatigue lives, and non-Masing model results in a more realistic fatigue life prediction for 316 LN stainless steel for both low and high strain amplitudes. The fatigue design curves obtained from the commonly used analytical low cycle fatigue equations were reexamined for 316 LN SS. The obtained design curves from Langer model and its modified versions are nonconservative for this type of material. Consequently, the authors suggest new optimized parameters to fit the given test data. The obtained curve using the currently suggested parameters is in better agreement with the experimental data for 316 LN SS.

Mechanical Behavior of Concrete-filled Steel Tubular Space Intersecting Nodes in High-rise Oblique Diagrid Tube Structures

In recent years, the researches on concrete-filled steel tubular (CFST) intersecting nodes mainly focused on the plane intersecting nodes, while that on space intersecting nodes with off-plane angles was relatively less. In this study, the nonlinear analyses of CFST space intersecting node models established in ABAQUS were performed under the monotonic axial compression and reciprocal axial tension-compression loads, respectively. The stress distributions of steel tubes and core concrete were analyzed, and the hysteresis characteristics and stiffness degradation of the node were studied. The in-plane angle, off-plane angle, out-of-plane constraint effect, steel tube diameter-to-thickness ratio, and core concrete strength were used as control parameters to analyze their effects on the mechanical behavior of the nodes. The results show that the bearing capacity of the nodes meets the design requirements, the hysteresis loop is full, the initial stiffness is large and the stiffness degrades slowly. The off-plane angle, out-of-plane constraint effect, steel tube diameter-thickness ratio and core concrete strength have significant effects on the bearing capacity and lateral stiffness of the nodes. In order to reduce the adverse effect of out-of-plane displacement, the space intersecting nodes in practical engineering can use reinforced floor beams or prestressd cables to impose out-of-plane constraint, and the recommended value of out-of-plane constraint effect is 10–30 kN/mm.

Evaluation of fatigue strength of carbon fiber reinforced plastics (CFRP) with various types of hybrid matrices

Polymer composite materials (PCM) have found wide application in various industries due to the ability to create low-weight products with specified operational properties. During operation, composite products are exposed to static and cyclic loads, climatic and many other factors. Evaluation of the fatigue strength of composite materials and the influence of various additives and modifiers on it is an urgent scientific and practical task. The article describes the technology of obtaining PCM with various types of hybrid matrices formed by the main binder material and the material representing an independent "liquid" phase in the composite structure. Based on the analysis of the kinetics of curing, anaerobic polymer material (Loctite 638), silicone elastomer (Unisil-9628) and synthetic wax were selected as the materials of the components of the "liquid" phase. Fatigue strength assessment tests were carried out by applying cyclically varying tension-compression loads to the samples. The load during cyclic tests was 70% of the static tensile strength of the samples. The residual strength was evaluated by testing the tensile strength of the samples until complete destruction after cyclic loading. The results of fatigue strength tests of carbon fiber plastics with various types of hybrid matrices (formed by various components of the "liquid" phase) are presented. The analysis of the results showed that the use of an anaerobic polymer material as a component of the "liquid" phase of the hybrid matrix makes it possible to increase both the initial static strength of the material (by ~ 1%) and the residual strength after cyclic loading (by ~ 11%) compared with these indicators obtained during the testing of control samples. After performing cyclic loading, carbon fiber plastics with anaerobic polymer material and silicone elastomer have an increase in residual strength compared to previously performed static tensile tests by ~ 8% and ~13%, respectively. The use of an anaerobic polymer material and silicone elastomer as a component of the "liquid" phase makes it possible to increase the modulus of elasticity of carbon fiber plastics after cyclic loading by ~ 13% and 5%, respectively, compared with the results of preliminary static tests.

Modelling dynamic failure of geometrical-similar concrete subjected to tension-compression loads: Effect of strain rate and lateral stress ratio

Concrete materials are widely acceptable to practical structural buildings exposed to not only uniaxial loads but also complicated stress states. Additionally, concrete structures under quasi-static loads may suffer from inevitable occasional dynamic loads. In this study, mesoscopic modelling on geometrical-similar concrete was conducted. Numerical experiments were performed under dynamic biaxial Tension-Compression loads with different strain rates (ranging from 10−5 s−1 to 1 s−1) and lateral stress ratios (ranging from −1.00 to 0). The effect of lateral stress ratio and strain rate on the mechanical damage behavior and size effect of geometrical-similar concrete was discussed. The numerical results indicate that the size effect on dynamic spindle compressive strength and dynamic lateral tensile strength are weakened with the increasing strain rate. However, the increasing lateral stress ratios bring different impacts on the size effect, namely enhancing the size effect on dynamic spindle compressive strength and weakening the size effect on dynamic lateral tensile strength. Moreover, considering the coupling effects between lateral stress ratio and strain rate, a dynamic Tension-Compression failure criterion for concrete was proposed. Finally, a static-dynamic universal size effect formula on the lateral tensile strength of concrete under dynamic Tension-Compression loading was established and verified.

Fatigue Studies On Aluminum 6061/SiC Reinforcement Metal Matrix Composites

<p>Fatigue is a process of progressive localized plastic deformation occurring in a material subjected to cyclic stresses and strains at high stress concentration locations that may culminate in cracks or complete fracture after a sufficient number of fluctuations. Fatigue testing is carried out using the ASTM D3479 with a notch or crack for investigating the initiation of crack. Several fatigue tests were conducted in tension-tension and/or tensioncompression loading at a frequency of 10Hz or sinusoidal wave’s frequency of 5Hz, and at constant-amplitude. The fatigue tests were interrupted by the researchers at regular intervals after a predetermined number of cycles to monitor crack advance and to observe the failure modes by various ways such as visual observation, digital camera, traveling microscope, CCD camera, etc.</p>

Fatigue life prediction and optimization of GFRP composites based on Failure Tensor Polynomial in Fatigue model with exponential fitting approach

In this study, a new fatigue life prediction and optimization strategy utilizing the Failure Tensor Polynomial in Fatigue (FTPF) model with exponential fitting and numerical bisection method for fiber reinforced polymer composites has been proposed. Within the experimental stage, glass/epoxy composite laminates with [Formula: see text], [Formula: see text], and [Formula: see text] lay-up configurations were fabricated, quasi-static and fatigue mechanical behavior of GFRP composites was characterized to be used in the FTPF model. The prediction capability of the FTPF model was tested based on the experimental data obtained for multidirectional laminates of various composite materials. Fatigue life prediction results of the glass/epoxy laminates were found to be better as compared to those for the linear fitting predictions. The results also indicated that the approach with exponential fitting provides better fatigue life predictions as compared to those obtained by linear fitting, especially for glass/epoxy laminates. Moreover, an optimization study using the proposed methodology for fatigue life advancement of the glass/epoxy laminates was performed by a powerful hybrid algorithm, PSA/GPSA. So, two optimization scenarios including various loading configurations were considered. The optimization results exhibited that the optimized stacking sequences having maximized fatigue life can be obtained in various loading cases. It was also revealed that the tension-compression loading and the loadings involving shear loads are critical for fatigue, and further improvement in fatigue life may be achieved by designing only symmetric lay-ups instead of symmetric-balanced and diversification of fiber angles to be used in the optimization.

Fatigue characteristics of sandwich composite joints in ships

The aim of this study is to investigate the fatigue characteristics of sandwich composite joints in ships based on the experimental and numerical methods. Sandwich composite L-joints are subjected to tension-compression, tension-tension and compression-compression fatigue loading at several load levels. Residual stiffness, strain, and surface temperature were measured during fatigue tests. The experimental results show that the sandwich composite L-joints have lower fatigue lives than expected and the fatigue load amplitude has a perceptible effect on the fatigue lives of the joints. In order to illustrate the influence of stress concentration on fatigue life of the joints, a quasi-static numerical analysis was conducted. Moreover, the fatigue damage mechanism and damage growth were revealed by experimental observation, stiffness curves and numerical stress distribution. Finally, a damage model based on the maximum displacements is proposed for the fatigue life prediction of the sandwich composite joints, and the results show that the predicted fatigue lives are in good agreement with the experimental ones.

Transient Hardening and R-value Behavior in Two-step Tension and Loading Reversal for DP980 Sheet

The present work deals with transient hardening and R-value behavior in two-step tension and loading reversal for an advanced high strength steel DP980. Mechanical properties under the loading paths were obtained through continuous tension-compression-tension, two-step tension and loading reversal experiments. The Yld2000-2d was employed to describe the initial yielding of DP980 1.0t through conducting monotonic tests. To characterize the transient behavior, a combined isotropic/non-linear kinematic hardening model, based on the 4-term Chaboche model, was selected. The Chaboche model was calibrated with the hardening curve in continuous tension–compression-tension loading. The transient behavior from the two-step tension and the loading reversal tests was then predicted by the model. The model performance was evaluated with the comparison of transient hardening and R-value from experiments and model predictions.

Experimental study on monotonic, cyclic mechanics and fatigue performance of pressed cone sleeve splices

The fundamental uniaxial monotonic, cyclic mechanical properties and fatigue performance of a novel mechanical coupler, namely pressed cone sleeve (PCS) splice, are examined and compared with that of the parallel threaded coupler (PTC) in this paper. The material properties and specimen details are firstly introduced. An experimental study consisting of 6 rebar specimens, 8 PCS specimens and 8 PTC specimens for the uniaxial monotonic and cyclic mechanical test is described to evaluate the strength as well as deformation characteristics of the mechanical splices. Then the fatigue performance of 17 PCS specimens and 16 PTC specimens are investigated. The effects of tension–tension loading and tension–compression loading path on fatigue performance are considered. The main macroscopic fatigue fracture morphology of PCS and PTC are also reported. The findings show that the strength of PCS is close to that of reinforcement and traditional PTC, and meets the strength requirements under the alternating tension and compression test with high stresses, and ductility requirements under the alternating tension and compression test with large plastic strains in the specifications. The slope of fatigue life S-N curve of PCS and PTC are basically consistent with the design curve given by GB 50010–2010 Code in China. However, the overall fatigue strength of mechanical splices including PCS and PTC is lower than the specified fatigue strength value of reinforcement to a large extent. Considering the remarkable connection efficiency and convenience of the novel PCS connection, on the premise of meeting the mechanics and fatigue strength, the PCS has relatively better technical advantages in the mechanical connection of rebars.

Uncertainty quantification in fatigue crack-growth predictions

The reliability of the damage tolerance approach to engineering design is affected by numerous sources of uncertainty that can lead to unsafe predictions, in turn jeopardizing the safety of structures. This work presents a robust stochastic framework for fatigue crack-growth predictions applied to a round bar under tension–compression loading conditions. Multi-source uncertainties were taken into account to derive the lifespan distribution for the bar in such a way to cover the uncertainties typically appearing in a structural integrity assessment. The sensitivity of each input variable was obtained and the influences of variables on the life predictions were derived and ranked accordingly.