A Novel Notion of Local and Nonlocal Deformation-Gamuts to Model Elastoplastic Deformation

Localization and nonlocalization are characterized as a measure of degrees of separation between two material points in material’s discrete framework and as a measure of unshared and shared information, respectively, manifested as physical quantities between them, in the material’s continuous domain. A novel equation of motion to model the deformation dynamics of material is proposed. The shared information between two localizations is quantified as nonlocalization via a novel multiscale notion of Local and Nonlocal Deformation-Gamuts or DG Localization and Nonlocalization. Its applicability in continuum mechanics to model elastoplastic deformation is demonstrated. It is shown that the stress–strain curves obtained using local and nonlocal deformation-gamuts are found to be in good agreement with the Ramberg–Osgood equation for the material considered. It is also demonstrated that the cyclic strain hardening exponent and cyclic stress–strain coefficient computed using local and nonlocal deformation-gamuts are comparable with the experimental results as well as the theoretical estimations published in the open literature.

Quasi-static compression behavior and microstructure changes in low-cost AA6061 composites

The workability study of the composites enhances the understanding of the degree of plastic deformation that can be employed on it. The current research work highlights the response of the low-cost aluminum composites reinforced with exhausted alkaline battery powders under quasi-static compression. The effect of reinforcements and aspect ratio against the strain hardening exponent and strength coefficients were investigated. The microstructural changes after quasi-static compression were studied and related to the changes in the property of the composites. The composite with 6 wt.% of reinforcement showed the least amount of porosity as 1.2%. In most of the cases, the maximum value of average strain hardening exponent with respect to axial strain was noted in the composites with 6 wt. % of reinforcement. The lowest aspect ratio of 0.5 showed the maximum workability in the composites. The average strength coefficient was found to be maximum (308.58 MPa) in the composite with 2 wt.% reinforcement. The elongated grains and slip bands were observed in the microstructure of the compressed specimens.

Two-Body Abrasive Wear Behavior and Its Correlation with Mechanical Properties of Aged AA6063 Alloy

This study aims to correlate the abrasive wear performance with mechanical properties, considering AA6063 Al-Mg-Si alloy as the model material. The selected alloy specimens are subjected to artificial ageing at 150 °C for an ageing duration ranging from 1 to 672 h, covering severely under-aged (SUA) to peak-aged (PA) to severely over-aged (SOA) states. Apart from the hardness and tensile properties, two-body abrasive wear properties are also evaluated for differently aged alloys in terms of wear rate, coefficient of friction, and roughness of the abraded surfaces. Furthermore, the generated wear debris, surface, and sub-surface of the abraded specimens are critically examined to reveal the micro-mechanisms of abrasion. The lowest amount of wear rate is observed for a PA alloy with maximum hardness, while the OA alloy exhibits a slightly lower wear rate than the UA alloy at a similar level of hardness. Statistical analyses of wear rate and various mechanical properties of all heat-treated alloys establish a strong negative linear correlation between the wear rate and hardness, yield strength, tensile strength, and strength coefficient; whereas, a positive linear correlation with the strain hardening exponent. Relationships between wear rate and different roughness parameters are also discussed. Under the investigated wear condition, the aged alloys endure significant plastic deformation; micro-plowing, micro-cutting, and delamination are found to be the predominant mechanisms during abrasion.

Micro-asperity Contact Area considering Strain Hardening for Metallic Materials

A novel micro-asperity contact area model, which considers influences of strain hardening, is proposed to describe contact area between a deformable sphere and a rigid flat for metallic materials. Firstly a generalized formula considering work-hardening behaviors (Pilling-up or Sinking-in) between contact area and interference is proposed for fully plastic regime based on the definition of plastic contact area index. Then a relationship to calculate the critical interference at the inception of fully plastic deformation is derived. In order to incorporate the transition from elastic regime to fully plastic regime, a quadratic rational form formula is proposed based volume conservation model for mixed elastoplastic regime. Therewith a modification is conducted to ensure continuity of contact area model at critical interference for fully plastic regime. Ultimately several representative models and experiment results are exhibited to analyze the availability of present model. It is noted considering work-hardening fully plastic contact area index is not a constant value of 2 for any metallic materials, which is a function of strain hardening exponent. Demonstration testifies that smoothness constraint is not necessary at the critical interferences. The prediction data of present model is consistent with experiment results contrasting that of other models. Current generalized contact area model considering influence of work-hardening results in a better understanding of the contact area between a deformable sphere and a rigid flat and indicates a probability to analyze contact characteristics of two mating rough surfaces accurately.

Effect of Bainite to Ferrite Yield Strength Ratio on the Deformability of Mesostructures for Ferrite/Bainite Dual-Phase Steels

The strength and plasticity balance of F/B dual-phase X80 pipeline steels strongly depends on deformation compatibility between the soft phase of ferrite and the hard phase of bainite; thus, the tensile strength of ferrite and bainite, as non-negligible factors affecting the deformation compatibility, should be considered first. In this purely theoretical paper, an abstract representative volume elements (RVE) model was developed, based on the mesostructure of an F/B dual-phase X80 pipeline steel. The effect of the yield strength difference between bainite and ferrite on tensile properties and the strain hardening behaviors of the mesostructure was studied. The results show that deformation first occurs in ferrite, and strain and stress localize in ferrite prior to bainite. In the modified Crussard-Jaoul (C-J) analysis, as the yield strength ratio of bainite to ferrite (σy,B/σy,F) increases, the transition strain associated with the deformation transformation from ferrite soft phase deformation to uniform deformation of ferrite and bainite increases. Meanwhile, as the uncoordinated deformation of ferrite and bainite is enhanced, the strain localization factor (SLF) increases, especially the local strain concentration. Consequently, the yield, tensile strength, and yield ratio (yield strength/tensile strength) increase with the increase in σy,B/σy,F. Inversely, the strain hardening exponent and uniform elongation decrease.

Full-Field Temperature Measurement of Stainless Steel Specimens Subjected to Uniaxial Tensile Loading at Various Strain Rates

This article presents a study on the effect of strain rate, specimen orientation, and plastic strain on the value and distribution of the temperature of dog-bone 1 mm-thick specimens during their deformation in uniaxial tensile tests. Full-field image correlation and infrared thermography techniques were used. A titanium-stabilised austenitic 321 stainless steel was used as test materials. The dog-bone specimens used for uniaxial tensile tests were cut along the sheet metal rolling direction and three strain rates were considered: 4 × 10−3 s−1, 8 × 10−3 s−1 and 16 × 10−3 s−1. It was found that increasing the strain rate resulted in the intensification of heat generation. High-quality regression models (Ra > 0.9) developed for the austenitic 321 steel revealed that sample orientation does not play a significant role in the heat generation when the sample is plastically deformed. It was found that at the moment of formation of a necking at the highest strain rate, the maximum sample temperature increased more than four times compared to the initial temperature. A synergistic effect of the strain hardening exponent and yield stress revealed that heat is generated more rapidly towards small values of strain hardening exponent and yield stress.

A Novel Flow Model of Strain Hardening and Softening for Use in Tensile Testing of a Cylindrical Specimen at Room Temperature

We develop a new flow model based on the Swift method, which is both versatile and accurate when used to describe flow stress in terms of strain hardening and damage softening. A practical issue associated with flow stress at room temperature is discussed in terms of tensile testing of a cylindrical specimen; we deal with both material identification and finite element predictions. The flow model has four major components, namely the stress before, at, and after the necking point and around fracture point. The Swift model has the drawback that not all major points of stress can be covered simultaneously. A term of strain to the third or fourth power (the “second strain hardening exponent”), multiplied and thus controlled by a second strain hardening parameter, can be neglected at small strains. Any effect of the second strain hardening exponent on the identification of the necking point is thus negligible. We use this term to enhance the flexibility and accuracy of our new flow model, which naturally couples flow stress with damage using the same hardening constant as a function of damage. The hardening constant becomes negative when damage exceeds a critical value that causes a drastic drop in flow stress.

Materials Testing for Mechanical Properties—Problems and Solutions

This appendix provides readers with worked solutions to 25 problems involving calculations associated with tensile testing and the determination of mechanical properties and variables. The problems deal with engineering factors and considerations such as stress and strain, loading force, sample lengthening, and machine stiffness, and with mechanical properties and parameters such as elastic modulus, Young’s modulus, strength coefficient, strain-hardening exponent, and modulus of resilience. They also cover a wide range of materials including various grades of aluminum and steel as well as iron, titanium, brass, and copper alloys.

Cyclic deformation behavior of an automotive material

The A356 Al-Si-Mg cast alloy is being used in the automotive industry to replace some heavy components due to its fabrication flexibility and high strength-to-weight ratio. This study was aimed at identifying cyclic deformation characteristics and fracture mechanisms of the A356 alloy in different material conditions. The microstructure consisted of primary a-Al matrix and eutectic regions containing Si particles of acicular (T5) and spherical (T6 and ModT6) morphologies. The ModT6 sample had a higher yield strength (YS) and ultimate tensile strength (UTS) but a lower strain hardening exponent than the T6 sample, while the T5 sample had a lower YS UTS but a higher initial strain hardening than the T6 sample. The T6 sample exhibited a higher cyclic hardening capacity and longer fatigue life. Crack initiation in both tensile and fatigue tests occurred at the sub-surface voids. Quasi-cleavage fracture characteristics in the T5 condition and dimple-like fracture features in the T6 and ModT6 were observed.