Mechanical Deformation Behavior Research Articles

Mechanical properties and deformation behaviour of TWIP steel at different strain rates

The mechanical properties of TWIP at different strain rates ranging from 5 s−1 to 500 s−1 were investigated by a VHS 160/100-20 high-speed tensile testing machine. The Johnson-Cook (J-C) dynamic constitutive model of TWIP steel was established based on the test results and verified by numerical simulation. Scanning electron microscopy (SEM), electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM) were used to analyse the microstructures of TWIP steel before and after tensile deformation. The findings demonstrate that under the tested strain rate, both the tensile strength and yield strength of TWIP steel increase with increasing strain rate, whereas the elongation decreases first and then increases. The strain rate of 100 s−1 is the turning point of the mechanical properties. The stack fault energy (SFE) is 26 mJ m−2 at room temperature, and the microstructure of TWIP steel before and after deformation is composed of single austenite, which demonstrates that only TWIP effect occurs. Dislocations accumulate along grain boundaries, forming structures such as dislocation cells and dislocation walls, causing stress concentration and promoting the formation of microcracks. With increasing strain rate, the dislocation cells are more obvious, and the thickness of the deformation twins decreases, resulting in an increase in the stress required for dislocations to cross the twin boundaries and material strengthening. The formation of nanoscale twins can not only effectively hinder the dislocation motion, but also provide space for dislocation slip and change the grain orientation, so that the slip system which is not conducive to deformation has a new orientation, resulting in a synergistic effect on strength and plasticity of TWIP steel. This work elucidates the relationship between the microscopic deformation mechanism and the macroscopic mechanical properties of TWIP steel at a specific strain rate, and a dynamic constitutive model is established, which can provide a reference for the application of TWIP steel in the design of anti-explosion and anti-impact structures.

A strategy for improving negative-Poisson's-ratio constraint effect and shape accuracy of metamaterials by regulating mechanical properties of elastomer with facile filler incorporation

Negative Poisson's ratio (NPR) metamaterials are widely used for their light weight and good shear resistance. However, the essential concave hollow structures in NPR materials may easily distort irregularly when the constraint effect of their solid materials is weak, especially for elastomer-based materials. Here, we introduced nano-scale carbon black (CB) particles into the NPR material based on thermoplastic polyurethane (TPU) elastomers to control the static and dynamic mechanical deformation behavior of the material, improving their constraint effect on the NPR structure. The results show that the modulus of the NPR structure is improved by 269% by adjusting the unit and rigid particle load. The Poisson's ratio of the NPR structure reaches as great as −1.3 via controlling the thickness/width ratio (TWR) of the unit. Meanwhile, finite element analysis verifies that when TWR is less than 0.5, increasing the modulus and yield strength of the composites can enhance the constraint on the NPR unit. Theoretical calculation shows that CB introduced into TPU can improve the shape accuracy of NPR structure. Therefore, the work could offer a new mechanical enhancing strategy for NPR materials, and its application potential is verified as a form of exoskeletons.

Investigation of the mechanical properties triple periodic minimal surfaces lattice structures with functional graded of porosity

In recent years, triple periodic minimal surfaces (TPMS) have attracted attention in many applications such as biomaterials, aerospace, defense industry etc. lightweight components with high strength and functionally graded material (FGM). In particular, the mechanical properties and deformation behavior of these structures under load should be examined. In this study, it was aimed to evaluate the manufacturability and mechanical performance of fixed pore size and functional graded porosity (FGP) lattice structures produced by fused deposition modelling (FDM) method. TPMS primitive and gyroid lattice structures designed in the dimensions of 20 × 20 × 20 mm with fixed 20% pore size and functional graded (FG) from 20% to 40% pore size were used in the experiments. In order to reveal the effects of pore size on mechanical performance, uniaxial compression tests were carried out. In addition, for the validation of the experimental results, compression tests with the finite element method (FEM) were simulated for each sample. In the two different pore size changes tested in the study, the gyroid lattice structure showed the highest mechanical performance compared to the primitive lattice structure. In addition, the FEM results were in good agreement with the experimental results.

Effect of interface structure and layer thickness on the mechanical properties and deformation behavior of Cu/Ag nanolaminates

We performed molecular dynamics (MD) simulations to study the effect of interface structure and layer thickness on the mechanical properties of multilayered Cu/Ag composite with Cu{111}//{111}Ag and Cu{100}//{100}Ag interfaces. The results indicate that deformation twinning is the dominant plastic deformation mode in the multilayer with Cu{100}//{100}Ag interfaces and differs from the dislocation slip in the models containing Cu{111}//{111}Ag interfaces. The interfaces in the Cu{111}//{111}Ag multilayer are significantly roughened by dislocation transmission across interfaces. The Shockley partial dislocations are difficult to cross Cu{100}//{100}Ag interface until the interface is twisted by deformation twinning. The deformation twinning in the Ag channel induces twists of Cu{100}//{100}Ag interface, facilitating twinning in Cu channels and dislocation transmitting across the Cu/Ag interface within twin bands. The mechanism results in strong interface roughening. The Cu{110}//{110}Ag interface is formed after the deformation twinning in models containing Cu{100}//{100}Ag interfaces, which exhibits extremely high shear strength than the Cu{100}//{100}Ag interface and produces a weak blocking effect on gliding dislocations.

Mechanical properties and deformation behaviors of Ti-5Al-5Mo-1Fe-1Cr alloy with duplex and single-phase microstructures

To clarify the differences of mechanical properties and deformation behaviors of a Ti−5Al−5Mo−1Fe−1Cr (wt.%) alloy with duplex and single-phase microstructures, the tensile properties and deformation modes of the alloy with these two different microstructures were studied systematically. The results show that the sample with the duplex microstructure has a tensile yield strength of 886 MPa, an ultimate tensile strength of 1075 MPa and an elongation of 21.5%. The sample with the single β phase has a relatively lower strength and a similar elongation. The sample with the duplex microstructure has a ductile fracture mode and deforms via dislocation slipping in the β matrix and spherical or plate-like α phases. The slip systems are {112}β<111>>β in β matrix, and {1122}α <1123>α and {1010}α <1210>α in α phase. In contrast, the single-phase sample has a quasi-cleavage fracture mode and deforms via dislocation slipping and stress- induced α″ martensite transformation, and the slip systems are {110}β <111>β and {112}β <111>β.

Effects of structure and strain rate on deformation mechanism of twin lamellar Al0.3CoCrFeNi alloys

Lamellar twined materials display simultaneous ultrahigh strength and high ductility, which is attributed to the interaction between twin boundaries and dislocation. However, deformation at the atomic level is rarely seen in experiments. To study the deformation properties and mechanical behavior of the lamellar twined Al0.3CoCrFeNi high-entropy alloys (HEA) sample, we applied the uniaxial tension by employing molecular dynamics (MD) simulations. The impact of various twin inclination angles, twin boundary spacing (TBS), and strain rates are investigated. The mechanical softening as the increasing TBS from 4a to 12a was observed, which corresponds to Hall – Petch relationship. The yield strength of the medium inclination angle (450, 600) records the minimum value with all various TBS due to the elastic energy being easier released. The strain-hardening phenomenon appears at these angles. The sample with an inclination angle perpendicular to the tension loading axis (900) displays the highest stress value. The shrinking migration twin has been observed in 00, 150, and 300 twin inclination angles. The migration and disappearance of initial TBs lead to grains being reoriented into the same orientation at 450 and 600. With twin orientations of 750 and 900, the TB is no longer as crisp and straight as the initial TB under the tension process. An extensive dislocation process occurs at higher strain values, and their interaction with TB leads to establishing the shear band. After that, twin boundaries within the shear band are almost destroyed. Besides, the results also indicate that the flow stress, ultimate strength, and Young's modulus rise with the rising strain rate and decreasing temperature.

Formation and deformation mechanism of the hierarchical diffusion layer in the laminated Ti/Ti–50Nb alloy

The diffusion layer is commonly formed in laminated metal composites (LMCs) and it continuously coordinates the deformation inconsistency between components of LMCs during deformation. By adjusting the phase structure of the diffusion layer, the mechanical properties and deformation behavior of the LMCs can be optimized. In this study, hierarchical diffusion layers with different multiphase architectures, caused by elemental gradients, are obtained in the investigated laminated Ti/Ti–50Nb (laminated Ti–TiNb) alloy by adjusting the cooling rate. TEM and EBSD were applied to investigate the microstructure evolution before and after the tensile deformation. The results indicate that the phase structure of the diffusion layer significantly affects the properties of laminated Ti–TiNb and the strain distribution during deformation. Compared with the "hard" diffusion layer accompanied by fine α phase precipitation, the "soft" diffusion layer with a large amount of α′′ phase precipitation is more conducive to the strain transfer between Ti and TiNb components. Each region in the “soft” diffusion layer exhibites different deformation behavior due to the difference in Nb element content and phase constitution. At last, the formation and deformation mechanism of the “soft” diffusion layer are analyzed in detail. This work provides a new strategy to develop high-performance laminated metal composites by structural design.

Mechanical properties and deformation behavior of functionally graded TPMS structures under static and dynamic loading

Mechanical properties and deformation behavior of functionally graded TPMS structures under static and dynamic loading

Experimental and Analytical Investigation on Flexural Behavior of High-Strength Steel-Concrete Composite Beams

This research investigated the flexural behavior of high-strength steel (HSS)—concrete composite beams. The effect of concrete strength on the load-deflection behavior, flexural capacity, and ductility of HSS—concrete composite beams was investigated. Four full-scale HSS—concrete composite beam specimens were tested under static load. The test results demonstrate that the failure mode of HSS—concrete composite beams is flexural failure of the steel member and compression fracture of concrete at mid-span. The HSS—concrete composite beam exhibits good mechanical performance and deformation behavior. The ultimate bending strength and ductility of HSS—concrete composite beams were improved with the increased concrete strength. The theoretical results demonstrate that the simplified plastic method overestimates the ultimate bending strength of HSS—concrete composite beams. The main reason is that only a small part of the steel beam bottom shows plastic strengthening, which is not enough to make up for the strength loss caused by the steel near the neutral axis failure to yield and the relative interface slip. The nonlinear method based on material constitutive model could predict the load-bearing capacity accurately. After analyzing the ultimate bending capacity of 192 sample beams, the simplified plastic method was modified, and the theoretical method for ultimate bearing capacity of HSS—concrete composite beams was proposed.

Mechanical Properties and Deformation Behavior of Metal Injection Molded Products with Cellulose Nanofiber

Metal Injection Molding (MIM) process is suitable for fabricating small and complex shaped metal parts with high production volume. In this study, in order to improve the MIM process, cellulose nanofibers (CNF) were focused. There are problems such as deformation during debinding and sintering due to the addition of a large amount of binder. On the other hand, the strength of the green compact decreased with decreasing binder contents. In this study, cellulose nanofibers were added with a binder during mixing in order to improve the handling of green compacts, and decrease the deformation during debinding and sintering. The effects of CNF contents on the mechanical properties were investigated. It was clarified that CNF is effective in improving the handleability of the debound compacts and suppressing deformation during sintering.

Development and Applications of 3D Printing-Processed Auxetic Structures for High-Velocity Impact Protection: A Review

Auxetic structures (AXSs) are a novel class of materials with unique mechanical deformation behavior associated with negative Poisson ratio. The combination of AXS configurations with various types of materials has unveiled a wide field of applications, including military high-velocity protection against explosions and ballistic projectiles. However, the characteristic geometric re-entrant model of AXSs imposes limitations and difficulties when using conventional manufacturing methods to assemble the structure lattice. Additive manufacturing (AM) has recently been explored as a more efficient and cost-effective method to fabricate AXSs, regardless of the type of material. This review paper focuses on the development and applications of AM processed AXSs. The review highlights the significance and great potential for this class of materials that can be produced relatively fast and at a low cost. The advantages of AXS/AM are expected to extend to important industrial sectors, particularly for military ballistic armor, where the feasibility for products with improved properties is critical. The use of AM offers a viable solution to overcome the difficulties associated with the conventional manufacturing methods, and thus offers greater design flexibility, cost efficiency, and reduced material waste. This review paper aims to contribute to the understanding of the current state-of-the-art and future research prospects for the production and applications of AXS/AM.

Effect of oxidation on mechanical properties of copper nanowire: A ReaxFF (reactive force field) molecular dynamics study

Nanostructures with high surface area to volume ratio, such as oxidized and coated Cu nanowires (NWs), exhibit unique mechanical properties due to their size and surface effects. Understanding the complex oxidation process of Cu NWs at nanoscale and quantifying its resulting effects on mechanical behavior and properties are significantly essential for effective usage of Cu NW devices in a wide range of applications in nanoelectronics. Here, we perform molecular dynamics simulations using ReaxFF (reactive force field) to investigate the oxidation process and mechanisms of [001]-oriented cylindrical Cu NWs and its contribution on the mechanical deformation behavior and material properties as a function of NW sizes. The relatively thin oxide CuxOy layer is formed on the surface of Cu NWs in an O2 environment, creating a core/shell (Cu/CuxOy) NW structure that played a key role in governing the overall tensile mechanical deformation behavior and properties of Cu NW. The formation of oxide layer effects, including the resulting interface and defects, leads to a reduction in the initial dislocation nucleation barrier, which facilitates the onset of plasticity and stress relaxation, ultimately resulting in a negative impact on the tensile strength, Young's modulus, yield stress and strain, and flow stress when compared to pristine counterparts. It is worth noting that the tensile mechanical response and properties of the Cu NWs are highly dependent on the pre-existing oxide shell layer associated with the size of NW, determining the overall mechanical performance and properties of Cu NWs.

Effects of cooling rate and cryogenic temperature on the mechanical properties and deformation characteristics of an Al-Mg-Si-Fe-Cr alloy

The Al-Mg-Si-Fe-Cr alloy was subjected to water quenching (WQ) and air quenching (AQ) after solution treatment for 30 min at 843 K followed by a peak artificial aging treatment at 453 K for 8 h. Precipitates of different sizes and precipitate free zone (PFZ) of different widths were obtained. Uniaxial tensile tests were conducted to investigate the effect of the microstructure and deformation temperature on the mechanical properties and deformation behavior of the WQ and AQ samples at 298 K and 77 K. The results showed that the yield strength and work hardening rate of the AQ samples were lower than those of the WQ sample. In addition, the strength and ductility of the two samples are significantly improved at cryogenic temperatures. Furthermore, quasi-in situ electron back scatter diffraction (EBSD) was conducted to investigate the orientation evolution of grains with strains of 1%, 3%, 7% and 10% for the two samples at 298 K and 77 K. The different orientation evolution of the two samples was caused by the nonuniform deformation in the PFZ and grain interior. The dislocation characteristics and fracture morphology were observed by transmission electron microscopy (TEM) and scanning electron microscopy (SEM), respectively. Because the rod-shaped precipitates hinder the dislocation movement, no obvious slip traces could be observed on the deformed surface of the AQ sample. In addition, two slip systems are activated for most grains of the WQ sample at 77 K, but only one slip system is activated at 298 K. Due to the weak grain boundaries deformed at 298 K, the stress applied to grains is consistent with the tensile direction. However, the grain boundaries are strengthened when tested at 77 K, and the stress field of the grain boundaries is more complex, resulting in the stress not only in the tensile direction. More slip systems are activated to coordinate the deformation, improving the ductility. TEM images reveal that the deformation of the PFZ is more severe for the AQ sample at 298 K than at 77 K. The deformation in the precipitate-free zone and within the grain was more homogeneous in the AQ sample at 77 K, which increased its ductility compared to the AQ sample at 298 K.

Combined effects of porosity and degree of saturation on the mechanical properties and deformation behaviour of rocks

To reveal the roles of pores and fissures in the rock-weakening effect of water, this study used porosity to quantitatively characterize pores and fissures in rocks. Based on the results from mechanical tests on rock specimens with different porosities and degrees of saturation, the combined effects of the porosity and water content on the mechanical properties and deformation behaviour of rocks were investigated. The test results indicated that the rock-weakening effect of water was markedly more significant if the pores and fissures in the rock were highly developed. The test data showed that the ratio of saturated specimen strength/dry specimen strength of porous rock can be even lower than 0.1. The least-squares regression method was used to derive the impact of rock porosity on rock weakening due to the effect of water. Based on the results, a practical engineering method for modifying the mechanical parameters of wet rocks with highly developed pores and fissures was proposed. This method can be used to calculate the stress–strain state of rocks more accurately.

Crystal orientation-dependent tensile mechanical behavior and deformation mechanisms of zinc-blende ZnSe nanowires

Crystal deformation mechanisms and mechanical behaviors in semiconductor nanowires (NWs), in particular ZnSe NWs, exhibit a strong orientation dependence. However, very little is known about tensile deformation mechanisms for different crystal orientations. Here, the dependence of crystal orientations on mechanical properties and deformation mechanisms of zinc-blende ZnSe NWs are explored using molecular dynamics simulations. We find that the fracture strength of [111]-oriented ZnSe NWs shows a higher value than that of [110] and [100]-oriented ZnSe NWs. Square shape ZnSe NWs show greater value in terms of fracture strength and elastic modulus compared to a hexagonal shape at all considered diameters. With increasing temperature, the fracture stress and elastic modulus exhibit a sharp decrease. It is observed that the {111} planes are the deformation planes at lower temperatures for the [100] orientation; conversely, when the temperature is increased, the {100} plane is activated and contributes as the second principal cleavage plane. Most importantly, the [110]-directed ZnSe NWs show the highest strain rate sensitivity compared to the other orientations due to the formation of many different cleavage planes with increasing strain rates. The calculated radial distribution function and potential energy per atom further validates the obtained results. This study is very important for the future development of efficient and reliable ZnSe NWs-based nanodevices and nanomechanical systems.

Hydrogen-related with the change in mechanical properties and deformation behavior of 316 L austenite stainless steel

Hydrogen-related with the change in mechanical properties and deformation behavior of 316 L austenite stainless steel

RESISTANT MECHANISM AND MECHANICAL PROPERTY OF MASONRY HYBRID STRUCTURES OF RAMMED EARTH-LIGHT WEIGHT STEEL MEMBERS

In previous researches, composite structure system made of rammed earth and steel member has been proposed, and mechanical properties and deformation behavior were investigated. This paper suggests an improved composite structural system made of rammed earth and light wight steel member. From the loading tests and a finite element analysis as parameter with states of open/close of wall and thickness of steel, the effective resistant mechanism with adjacent composite structure blocks is appeared, and the combined effect for strength and rigidity is obtained. From analytical results, the relationship between the stress state and the thickness of steel members is investigated.

Mechanical properties and deformation behaviors of the hydroxyl-terminated polybutadiene and ammonium perchlorate interface by molecular dynamics simulation

The interfacial structure and deformation behaviors have considerable influences on the structural reliability and durability of the hydroxyl-terminated polybutadiene (HTPB) solid rocket propellant. In this work, an all-atom molecular dynamics (MD) simulation was adopted to investigate mechanical properties and damage behaviors of the HTPB and ammonium perchlorate (AP) interface. The modified polymer consistent force field was implanted to describe intra- and intermolecular interactions. The effects of loading rate, temperature, and moisture content on the interfacial strength and tensile curves were discussed. The simulation results show that the interfacial strength and modulus exhibit an increasing tendency when the loading rate increases. However, increasing the temperature and moisture content will lead to a decrease in the interfacial strength. Two interfacial tensile modes distinguished by the mass density curve were adopted and compared to reveal the internal deformation process. The AP-HTPB interfacial deformation initially occurs inside the HTPB bulk due to its lower mechanical strength than the interface and then gradually expands to the interface region. Furthermore, a linear extrapolation based on phenomenological results was used to reveal the discrepancy in scale between experiments and the MD simulation.

Experimental Investigation on the Deformation Characteristics and Mechanical Behaviors of Tectonic Coal under Complex Unloading Confining Pressure

Conventional and cyclic unloading tests with different unloading rates were conducted to study the influences of unloading patterns and rates on the deformation characteristics and mechanical properties of tectonic coal. The results demonstrate that, under continuous unloading, a lower unloading rate promotes an increase in the circumferential strain but inhibits increases in axial strain. A lower unloading rate was found to be able to promote volume expansion under the cyclic unloading path, and the axial, circumferential, and volume strains increased stepwise with the unloading levels, but the increment of the strains decreased with the number of cycles in the same unloading level. It was easier for tectonic coal to reach the elastic limit by a low speed unloading rate when the unloading level was small, and volume dilatation was promoted when the unloading level was large. In both unloading patterns, the tangential modulus and the Poisson ratio were proportional to the unloading rate. Compared with continuous unloading, the cyclic unloading pattern was found to have a significant delaying and inhibiting effect on damage expansion, and thus higher mechanical strength and more structurally stable tectonic coal responses were observed.

Metal-Coordinated Dynamics and Viscoelastic Properties of Double-Network Hydrogels

Biological soft tissues are intrinsically viscoelastic materials which play a significant role in affecting the activity of cells. As potential artificial alternatives, double-network (DN) gels, however, are pure elastic and mechanically time independent. The viscoelasticization of DN gels is an urgent challenge in enabling DN gels to be used for advanced development of biomaterial applications. Herein, we demonstrate a simple approach to regulate the viscoelasticity of tough double-network (DN) hydrogels by forming sulfonate-metal coordination. Owing to the dynamic nature of the coordination bonds, the resultant hydrogels possess highly viscoelastic, mechanical time-dependent, and self-recovery properties. Rheological measurements are performed to investigate the linear dynamic mechanical behavior at small strains. The tensile tests and cyclic tensile tests are also systematically performed to evaluate the rate-dependent large deformation mechanical behaviors and energy dissipation behaviors of various ion-loaded DN hydrogels. It has been revealed based on the systematic analysis that robust strong sulfonate-Zr4+ coordination interactions not only serve as dynamic crosslinks imparting viscoelastic rate-dependent mechanical performances, but also strongly affect the relative strength of the first PAMPS network, thereby increasing the yielding stress σy and the fracture stress at break σb and reducing the stretch ratio at break λb. It is envisioned that the viscoelasticization of DN gels enables versatile applications in the biomedical and engineering fields.