Cyclic Deformation Properties Research Articles

Experimental study on cyclic deformation properties of saturated Fujian sand at different loading frequencies

In this study, a series of undrained cyclic torsional shear tests were conducted to investigate the effect of cyclic loading frequency f on the pre-liquefaction (shearing contractive (SC) period and initial shearing dilative (ISD) period) and post-liquefaction (late shearing dilative (LSD) period) deformation properties of saturated Fujian sand. The secant shear modulus G and damping ratio λ in the entire cyclic loading process, and the unloading tangent shear modulus GL1 and flow deformation tangent shear modulus GL2 in the ISD and LSD periods were adopted to quantitatively characterize the evolution of hysteresis loop with an increase in shear strain amplitude γa. The test results show that the effect of f on G of saturated Fujian sand in the SC period is not apparent. However, all the G-γa, GL1-γa, and GL2-γa curves in the ISD and LSD periods showed a downward trend with an increase in f. This study also proposes a modified method for calculating λ to compensate for the analytical error caused by the non-closure of hysteresis loop. Compared with the classical curves that mainly applied in geotechnical engineering, the λ first increases and then decreases with the increase of γa. Furthermore, the λ evaluated by the modified method is approximately 10%–15% more than the λ evaluated by the traditional method when the λ reaches its peak value.

Characterization of the Fatigue Behaviour of Low Carbon Steels by Means of Temperature and Micromagnetic Measurements

Investigations on low carbon (non- and low-alloy) steels were conducted in form of load increase tests (LIT) and constant amplitude tests (CAT) to find the correlation among material behaviour, mechanical load, and the type of NDT method. With the help of preprogrammed load-free sequences, the thermal impact on magnetic Barkhausen noise (MBN) measurement can be avoided, so that the cyclic deformation properties of material responses can be interpreted more precisely. The results indicate differences between the change in temperature and the MBN-derived variable during LITs and CATs regarding the demonstration of the incubation stage and the cyclic hardening behaviour.

The tension-compression behavior of gradient structured materials: A deformation-mechanism-based strain gradient plasticity model

Gradient structured (GS) metals can simultaneously achieve high strength and high ductility, which is the pursuit of structural materials. Abundant studies have pointed out that significant kinematic hardening is key to their strength-ductility combination. Unfortunately, few constitutive models were established to simulate and analyze the characteristic kinematic hardening behavior of GS metals. Thus, a systematic and deep understanding of the relationship between graded microstructure and the resulting macroscopic response needs further effort. In this work, we develop a strain gradient plasticity model that considers plasticity heterogeneities from the grain to the sample scale. A back stress model, which accounts for the dependency of dislocation pileups on grain size, is established to describe the cyclic deformation properties of GS materials. The established model unifies the concepts of geometrically necessary dislocations accommodating plasticity heterogeneities, grain size-dependent back stress, and reversible dislocation motion during reverse loading into a strain gradient plasticity framework. A finite element implementation of the model quantitatively predicts the uniaxial tensile and tensile-compressive responses of a GS copper bar as well as of homogeneously grained reference samples. The simulation indicates that the enhanced kinematic hardening of GS copper results mainly from fine grains in the GS layer and contributes to the considerable ductility of the GS material. The strain gradient cyclic plasticity model enables future investigation of the cyclic/fatigue behavior of GS materials, which is vital for the engineering application.

Cyclic deformation properties of artificial leather for sports equipment

Cyclic deformation properties of artificial leather for sports equipment

The effect of material cyclic deformation properties on residual stress generation by laser shock processing

Laser shock processing (LSP) is a mechanical surface treatment to induce a compressive residual stress state into the near surface region of a metallic component. The effect of the cyclic deformation properties of ductile materials on the final residual stress fields obtained by LSP is analysed. Conventional modelling approaches either use simple tensile yield criteria, or isotropic hardening models if cyclic straining response is considered for the material during the peen processing. In LSP, the material is likely to be subject to cyclic loading because of reverse yielding after the initial plastic deformation. The combination of experiment and modelling shows that the incorporation of experimentally-determined cyclic stress-strain data, including mechanical hysteresis, into material deformation models is required to correctly reflect the cyclic deformation processes during LSP treatment and obtain accurate predictions of the induced residual stresses.

Effect of heat treatment on cyclic deformation properties of Fe–26Mn–10Al–C steel

Fully reversed tensile–compression low-cycle fatigue tests were performed at room temperature under strain amplitude of 0.4%. The monotonic tensile results show that Fe–26Mn–10Al–C steels are fully austenite and the optimal combination of ultimate tensile strength and total elongation was present at 950 °C with 65 GPa %. The fatigue results show that the specimen at 1050 °C has the maximum fatigue life of 162,000 cycles, which is much longer than twinning-induced plasticity (TWIP) steels of the same strain amplitude. The hot-forging specimen shows high similarity with TWIP steels with rapid initial cyclic hardening followed by cyclic softening and cyclic saturation. After solution heat treatment, it is noteworthy that, after rapid initial cyclic softening, another rapid cyclic hardening and a following decrease with fluctuation were observed at 1000 °C. It is reasonable to believe that it is caused by κ-carbides precipitated during cyclic deformation. Another interesting phenomenon is cyclic stress subsidence observed at 1050 °C during its saturation stage at the last quarter of the fatigue life, and the span is about 12.5% of whole fatigue life.

Estimation of the cyclic shear stress‐strain curve from tensile properties for steels

AbstractThe objective of this study is to derive a method for estimating the cyclic shear deformation properties (the cyclic shear strength coefficient and cyclic shear strain hardening exponent) of steels from common tensile properties. For this purpose, equations that relate the cyclic shear strength coefficient and cyclic shear strain hardening exponent to the monotonic tensile properties (the ultimate tensile strength and monotonic yield strength) are established on the basis of the 15 kinds of steel taken from the technical literature. Validity of some of the more commonly used methods of estimating cyclic shear deformation properties is examined and compared to the correlations proposed in this study. The proposed method is shown to be better used to estimate the cyclic shear deformation properties.

Uniaxial cyclic elasto-plastic deformation and fatigue failure of API-5L X65 steel under various loading conditions

The cyclic elasto-plastic deformation and fatigue failure properties of API-5L X65 steel was characterised under monotonic, high cycle fatigue, strain controlled low cycle fatigue, and stress controlled ratchetting loading regimes. The steel combines high strength, which increases with strain rate under monotonic loading, with high fatigue limit/yield strength ratio. It is found that the steel exhibits non-Masing and cyclic softening behaviours. Low cycle fatigue lifetime decreased with increase in total strain amplitude and plastic strain amplitude. It is shown that, under uniaxial fully reversed loading, the Chaboche model with three backstresses is capable of describing the cyclic hysteresis stress-strain curves of the steel. Ratchetting lifetime of the steel decreased with increase in ratchetting strain and increase in both mean stress and stress amplitude; the stress amplitude however dominates the damage process compared to mean stress.

Low Cycle Fatigue Behaviour of DP Steels: Micromechanical Modelling vs. Validation

This study aims to simulate the stabilised stress-strain hysteresis loop of dual phase (DP) steel using micromechanical modelling. For this purpose, the investigation was conducted both experimentally and numerically. In the experimental part, the microstructure characterisation, monotonic tensile tests and low cycle fatigue tests were performed. In the numerical part, the representative volume element (RVE) was employed to study the effect of the DP steel microstructure of the low cycle fatigue behavior of DP steel. A dislocation-density based model was utilised to identify the tensile behavior of ferrite and martensite. Then, by establishing a correlation between the monotonic and cyclic behavior of ferrite and martensite phases, the cyclic deformation properties of single phases were estimated. Accordingly, Chaboche kinematic hardening parameters were identified from the predicted cyclic curve of individual phases in DP steel. Finally, the predicted hysteresis loop from low cycle fatigue modelling was in very good agreement with the experimental one. The stabilised hysteresis loop of DP steel can be successfully predicted using the developed approach.

Cyclic deformation properties of knitted sportswear fabrics by different test methods

Cyclic deformation properties of knitted sportswear fabrics by different test methods

Fatigue Deformation Behavior of Fe-Mn-C-(Al) TWIP Steels

The effects of Al on the monotonic deformation behavior of Fe-Mn-C twinning-induced plasticity (TWIP) steels have been extensively investigated; however, how the addition of Al affects the fatigue properties of these steels is unknown. The present paper deals with the cyclic deformation properties of Fe-22Mn-0.6C-0Al and Fe-22Mn-0.6C-3Al steels by means of total strain-controlled low-cycle fatigue tests. The total strain amplitude ranges from 0.002 to 0.01. The evolved microstructures of fatigued samples were observed by transmission electron microscopy. Results show that the addition of Al has a significant effect on the cyclic deformation behavior, fatigue lifetime and evolved microstructure of Fe-Mn-C TWIP steel.

114 形状記憶複合材料の通電加熱による繰返し変形特性(OS1-1 疲労・腐食特性,OS1 高機能材料の開発,特性評価と応用)

114 形状記憶複合材料の通電加熱による繰返し変形特性(OS1-1 疲労・腐食特性,OS1 高機能材料の開発,特性評価と応用)

An improved method for estimation of Ramberg–Osgood curves of steels from monotonic tensile properties

AbstractIn the present study, first a method for estimating cyclic yield strength is improved and compared using the experimental data of 121 steels from literature. Correlations between cyclic deformation properties (K′ and n′) and monotonic tensile data are then investigated, and a simple method requiring only the monotonic tensile properties is developed for estimation of the Ramberg–Osgood curve. Prediction capability of the proposed method is not only evaluated using the aforementioned 121 steels, but also compared with several commonly used methods that are available in the literature. The proposed correlations are shown to predict the cyclic deformation properties of most of considered steels reasonable well.

OS0206-172 形状記憶合金と形状記憶ポリマーによる複合材料の開発とその繰返し変形特性

OS0206-172 形状記憶合金と形状記憶ポリマーによる複合材料の開発とその繰返し変形特性

軸方向鉄筋の破断防止策を施したSFRC柱の二方向繰り返し耐荷特性に関する実験的研究

本研究では，「横拘束筋間隔」，「柱塑性ヒンジ部の軸方向鉄筋とコンクリート間の付着の有無」および「載荷経路」を水準とした鉄筋コンクリート（RC）柱の二方向繰り返し載荷実験を実施し，特にRC柱破壊領域の軸方向鉄筋とコンクリート間の付着の有無が軸方向鉄筋の座屈・破断性状および内部コンクリートの破壊進展に与える影響について検証した．これまでの二方向載荷下でのRC柱，鋼繊維補強コンクリート（SFRC）柱ならびに中間補強筋付きRC柱の耐荷特性も含めて検討した結果，1）アンボンド型SFRC柱とすることにより，SFRC柱と比べ，軸方向鉄筋の破断個所が少なくなる，2）アンボンド型SFRC柱は横拘束筋間隔に関係なくSFRC柱を含む他のRC柱よりも高い強度保有率を大変位領域まで維持できる，など多くの知見を得た．

Cyclic deformation and fatigue of extruded Mg–Gd–Y magnesium alloy

Cyclic deformation and fatigue of extruded rare-earth Mg–8.0Gd–3.0Y–0.5%Zr (GW83) magnesium (Mg) alloy were experimentally investigated by carrying out fully reversed strain-controlled tension–compression experiments along the extrusion direction with the strain amplitudes varying from 0.275% to 5.0%. Monotonic tension and compression stress–strain curves display a smooth transition from elastic to elastic–plastic deformation and exhibit a fairly yielding symmetry. Different from conventional Mg alloys, the material shows near-symmetric stress–strain hysteresis loops and marginal cyclic hardening with almost zero mean stress in the fully reversed strain-controlled experiments conducted. With increasing number of loading cycles, a transition of stress–strain response from concave-down shape to sigmoidal shape occurs in both tension and compression reversals when the strain amplitudes are larger than 2.0%. The strain-life fatigue curve displays a similar feature to that of conventional Mg alloys: A detectable transition from low-cycle region to high-cycle region occurs at a kink point in the vicinity of a strain amplitude of 0.75%. The cyclic deformation and fatigue properties of GW83 Mg alloy and the associated cyclic deformation mechanism are discussed and compared with those of a typical conventional Mg alloy.

A method of predicting cyclic stress–strain curve from tensile properties for steels

Cyclic loading can significantly alter the monotonic deformation resistance of a material. Knowledge of the cyclic deformation behavior of a material is essential for reliable life calculations of cyclically loaded structures. As monotonic tensile properties are commonly available or easily obtainable from a simple tension test, the objective of this study was to derive a method for estimating the cyclic deformation properties of steels from common tensile properties and hardness. A variety of correlations and relationships among hardness, tensile properties, and cyclic deformation properties were developed for fifty-seven steels included in this study. Several correlations and relations from the literature among the aforementioned properties were also examined and compared to the correlations and relationships proposed in this study using a different set of data from sixty-six steels. Implications of the proposed cyclic deformation behavior estimation method on fatigue life predictions are also discussed.

An experimental study on cyclic deformation and fatigue of extruded ZK60 magnesium alloy

Cyclic deformation and low-cycle fatigue properties of extruded ZK60 magnesium alloy were experimentally investigated by carrying out fully reversed strain-controlled uniaxial tension–compression fatigue experiments along the extrusion direction. The material shows significant yielding asymmetry under monotonic tension and compression. Marginal cyclic hardening is manifested at all the strain amplitudes tested. The shape of the stress–strain hysteresis loop and the mean stress strongly depend on the strain amplitude. When the strain amplitude is higher than 0.52%, asymmetric shape of the stress–strain hysteresis loop and significant tensile mean stress develop. With intermediate strain amplitudes (0.45–0.52%), the stress–strain hysteresis loop evolves from an asymmetric shape at the initial loading cycles to a symmetric shape after approximately 10% fatigue life, accompanied by moderate saturated mean tensile stresses. Symmetric stress–strain hysteresis loop with zero mean stress is observed for the strain amplitudes lower than 0.45%. It is suggested that the twinning–detwinning process plays a dominant role for the deformation at high strain amplitudes while dislocation slip dominates at the low strain amplitudes. The strain–life fatigue curve shows a kinking plateau in the vicinity of 0.52% strain amplitude. Different crack initiation mechanisms are proposed in the two strain amplitude ranges divided by the plateau in the strain–life curve. The material displays a tensile cracking growth behavior and the Smith, Watson, and Topper (SWT) fatigue parameter is appropriate for the description of the fatigue life. The residual twins after fatigue were examined by light microscopy and the fracture surfaces were observed by scanning electron microscopy (SEM). Distinctive features were observed depending strongly on the strain amplitudes. The observed microscopic features are discussed with respect to possible crack initiation and propagation mechanisms.

Microstructure – cyclic deformation property relationships of biodegradable di-crystalline triblock copolymers

The synthesis, morphological characterization and cyclic deformation behaviour of a double crystalline triblock copolymer containing crystalline poly( l-lactide) (PLLA) or random copolymer of poly( l-lactide) and polycaprolactone (PCL) hard segment and a random copolymer of polycaprolactone and poly(trimethylene carbonate) (PTMC) soft segment are presented. The hard segment content was varied via the CL/LLA molar ratio to produce copolymer with distinct morphologies. Differential scanning calorimetry (DSC), wide-angle X-ray scattering (WAXS) and atomic force microscopy (AFM) measurements confirmed the existence of a microphase-separated structure and the domain size was largely affected by the hard segment PCL content. Furthermore, combined measurements of WAXD and stress – strain curves revealed the molecular mechanism responsible for the superior strain recovery behaviour. It was formed that the permanent set can be largely reduced by incorporating PCL into PLLA hard segment and the strain recovery is enhanced by the ease of PCL crystal rotation upon retraction.

Effects of continuous cast section size on torsion deformation and fatigue of induction hardened 1050 steel shafts

This study investigates the influence of continuous cast section size on the mechanical performance of induction hardened parts produced from steel bars. SAE 1050 steel from commercially produced Jumbo Blooms, Blooms, Rotary Round, and Billet were hot rolled into round bars with diameters of 37–44 mm. These bars were then normalized, machined into test specimens, the gauge sections were polished, and the specimens were case-hardened by induction hardening. Torsional monotonic and fully reversed cyclic fatigue tests were conducted to study the effect of the initial continuous cast section size on deformation and fatigue behaviors. Reduction ratios in this study ranged from a low of 20.4:1 for the Billet, up to a high of 142:1 for the Jumbo Bloom. Test results indicate that the continuous cast section size has only small effects on the torsion monotonic and cyclic deformation properties and negligible effect on the torsion fatigue performance. Small differences observed in deformation and fatigue properties between the four processes are attributed mostly to the variation in case and core hardness levels caused by small differences in chemistry, particularly carbon content. Variations in sulfur content also influence ductility and fatigue behavior. At high strains, the cracks initiated in shear as longitudinal cracks for all four materials. At low strains, the cracks initiated at the surface in tension as spiral cracks due to normal tensile stresses.