Mechanical Deformation Behavior Research Articles

Molecular dynamics simulation to investigate effect of deformation of copper-based graphene for continuous/adjacent indentation

The fabrication of periodic nanostructures has garnered significant attention. Despite the investigation into the mechanical properties and deformation behaviors of graphene coated on metal surfaces during single indentation, there remains a dearth of research on the mechanical response and deformation behaviors of graphene/Cu systems, as well as the effects of different crystal orientations during continuous nanoindentation. The present study employed molecular dynamics simulations to investigate the effects of crystal orientation and coated graphene on surface morphology, elastic recovery, and dislocation evolution in Cu and graphene/Cu systems under continuous indentation-induced deformation. The results revealed that the force required for continuous indentation was approximately 1.36 times higher than that for initial indentation at the same depth on Gr/Cu, indicating a significant work hardening effect induced by the first indentation. Moreover, the continuous indentation enhances the surface pile-up effect and promotes the formation of more atoms in the overlap region between adjacent indentations. The presence of graphene coatings significantly influences the contact area, suppressing dislocation nucleation while increasing dislocation density. Furthermore, during continuous indentation, the depth at which dislocation nucleation occurs is shallower compared to that observed during initial indentation. The subsurface damage caused by the initial indentation was comparatively more severe than that induced during continuous indentation. Notably, the extent of dislocation propagation resulting from continuous indentation on graphene/Cu surpassed that observed on Cu alone. These findings significantly contribute to our comprehension of the metal-graphene interaction mechanism during continuous indentation and offer valuable insights for optimizing indentation quality.

Mechanical properties and deformation mechanism of defected NiCrCoFeMn alloys

This study provides new insights into the mechanical properties and deformation behavior of single-crystal NiCrCoFeMn high entropy alloys (HEAs) containing circular and block defects, using molecular dynamics (MD) simulations. It explores the effects of varying defect sizes, substrate temperatures, and strain rates on the material’s response under uniaxial tension. The results reveal that mechanical properties such as yield stress and Young's modulus decrease as defect size increases. Specifically, the stress concentration factor (SCF) increases as the radius of circular defects expands from 15 to 30Å, and initially rises with block defects up to 35.36×35.36Ų, but decreases as their size increases. The deformation mechanism starts with local strain nucleating around the circular defect and at the corners of the block defect, underscoring the significant role of defect shapes in initiating deformation across all samples. During uniaxial tension, phase transformations occur, resulting in the formation of stacking faults (SF), twinning (T), and partial dislocations (PD). Additionally, higher strain rates markedly boost the development of HCP, BCC, and amorphous structures. Dislocations initially form around defect shapes and extend towards free surfaces as strain escalates. Predominant dislocations during deformation include Shockley partial and Stair-rod dislocations. The total dislocation length increases with smaller defect sizes and higher strain rates, while it decreases at elevated temperatures due to enhanced atomic mobility, which facilitates dislocation movement and annihilation.

Layer thickness dependent strengthening and strain delocalization mechanism in CuTa nanopillars with nanoscale amorphous/amorphous interfaces

Introducing amorphous/amorphous interfaces in metallic glasses offers an effective strategy to address the strength-plasticity trade-off by suppressing the strain localization. Elucidating the underlying size-dependent deformation mechanisms is crucial for designing strong and ductile amorphous nanolayered materials. Herein, molecular dynamics simulations are conducted to investigate the deformation behaviors of Cu70Ta30/Cu30Ta70 amorphous/amorphous nanopillars (AANPs) under compression, focusing on the intrinsic size effect of amorphous layer thickness. The results indicate a critical layer thickness of approximately 6.7 nm, below which an inverse Hall-Petch relation occurs. This transition is attributed to a shift in dominant deformation mode from the necking and localized deformation to the relatively homogeneous deformation as the layer thicknesses decreases. These A/A interfaces could be considered as a third medium phase in nanolaminates, especially when the thickness is very low, down to only a few of nm. The mechanical properties and deformation behavior of transitional interface phase lie between those of soft and hard phases, balancing heterogeneous deformation between hard and soft layers and resulting in homogeneous flow deformation of specimen with thinner amorphous layer. These findings provide insight for designing ductile amorphous materials through architecting nanoscale amorphous/amorphous interfaces.

Deformation mechanism and resultant microstructural characteristics in extruded dilute Mg-0.1Bi-0.1Sn alloy with bimodal-sized grain structure under compression

In this study, we examine in detail the hot deformation mechanism and dynamic recrystallization (DRX) behavior in a novel precipitate-free Mg-0.1Bi-0.1Sn alloy during hot compression conducted at 200–350 °C, with strain rate of 0.33–10 s−1. The obtained correlation coefficient is 0.98024, indicating that the present constitutive equation can adequately predict the hot deformation behavior of the studied alloy. The calculated average activation energy is 180.427 kJ/mol. According to the processing maps, the ideal processing areas correspond to the conditions of 325–350 °C/0.33–1 s−1. Under the low Z deformation condition, the basal slip dominates at the initial and later stages, while the pyramidal slip is dominate at the intermediate stage. Meanwhile, the continuous dynamic recrystallization (CDRX) and discontinuous dynamic recrystallization (DDRX) processes co-occur during hot compression. More specifically, in the initial stage, DDRX dominates over the DRX mechanism, and is accompanied by twinning induced dynamic recrystallization (TDRX). In the intermediate stage, CDRX, TDRX and DDRX prevail as the dominant DRX mechanisms. Throughout the strain stage, DDRX dominates over the DRX mechanism. The occurrence of TDRX and CDRX is beneficial to weakening the texture intensity and promoting the development of CD-tilted texture.

Numerical and Experimental Investigation of the Effect of Overlapping Angle on Strength and Deformation of Curved Plate Joined Using Arc Welding Process

This research presents a comprehensive numerical and experimental investigation into the influence of overlapping angles from 30° to 100° with a 5° increment on the mechanical strength and deformation behaviour of curved plates joined using the arc welding process. This study employs Finite Element Analysis (FEA) to simulate the welding process and assess the stress distribution and deformation across the welded joint. The simulations complemented by experimental trials; wherein curved plates joined at varying overlapping angles using arc welding. Mechanical tests, including tensile and bending tests, conducted to evaluate the joint strength and deformation characteristics. The results reveal a significant impact of the overlapping angle on the welded joint's performance. Specifically, an optimal overlapping angle identified, which maximizes joint strength while minimizing deformation. The findings contribute to a better understanding of the welding process for curved plates and offer practical guidelines for optimizing welded joint design in engineering applications.

Molecular dynamics study on mechanical properties and plastic deformation mechanism of GNPs/Mg composites

This study utilizes molecular dynamics methods to embedded GNPs (graphene nanosheets) of uniform size and thickness into single crystal Mg, establishing a GNPs/Mg composite model. The mechanical properties and plastic deformation behavior of the composite under various compression conditions (volume fraction of GNPs, strain rate, and temperature) are investigated. The results indicate that uniformly distributed GNPs enhance load transfer and provide dispersion strengthening, effectively improving the composite's mechanical properties. As the volume fraction of GNPs increases, the yield stress of the composite first increases and then decreases. When the volume fraction of GNPs is 3.9 %, both the yield stress and Young's modulus of the composite reach their maximum values of 9.16 GPa and 108.83 GPa, respectively. The uniformly dispersed GNPs constrain dislocations on prismatic and pyramidal planes, thereby suppressing twinning deformation. Consequently, dislocation slip predominantly occurs as 1/3<-1100> partial dislocations on the (0001) basal plane. Young's modulus is not sensitive to strain rate; as the strain rate increases from 0.0025 Å·ps⁻¹ to 0.0125 Å·ps⁻¹, the yield stress rises from 8.50 GPa to 10.42 GPa. At high strain rates, only some dislocation sources are activated, and the number of 1/3<-1100> partial dislocations decreases with increasing strain rate. Within the temperature range of 100 K to 500 K, both the elastic modulus and yield stress of the GNPs/Mg composite decrease with increasing temperature.

MPFEM investigation on densification and mechanical structures during ferrous powder compaction

Metal powder compaction is a crucial process in powder metallurgy, significantly affecting the final properties of compacts. However, the quantitative characteristics of multi-scale mechanical structures and the microscopic densification behavior, taking into account the influence of friction conditions, remain unclear. This study utilises a two-dimensional multi-particle finite element method to analyse the ferrous powder compaction. The evolution of powder densification, powder deformation and multi-scale mechanical behaviour under different friction coefficient conditions are analyzed quantitatively and qualitatively. Results reveal that powder densification occurs in distinct stages, with lower friction coefficients promoting greater powder densification, as observed from relative density and coordination number. Additionally, as the axial strain increases, plastic strain gradually rises whilst roundness decreases. Higher friction coefficients are associated with higher equivalent plastic strain but lower powder roundness. The Von Mises stress exhibits different stages of increase with the increment of axial strain. Powders with lower friction coefficients exhibit lower levels of Von Mises stress. As axial strain increases, the number, length, strength and direction coefficient of force chains undergo different evolution processes. Force chains exhibit longer length, fewer numbers, lower strength and lower direction coefficients at lower friction coefficients.

Deformation behavior of Gd alloyed CoCrFeNi high entropy alloy at high temperature under the influence of local nano-ordered structure and misorientation

The thermomechanical processing (TMP), which is an industrial process that includes deformation and heat treatment, represents a novel approach to enhancing the mechanical properties of metallic materials. However, it requires extensive research on the high-temperature deformation behavior of alloys during its application process. The present study conducts hot compression tests at 700 °C and 800 °C, as well as detailed microstructural characterization of the deformed material after hot deformation, to comprehensively discuss the mechanical properties and deformation behavior at high temperature of the (CoCrFeNi)100-xGdx (x = 0, 0.5, 1, 2, 3 at.%) HEAs. The (CoCrFeNi)100-xGdx HEAs exhibit an excellent combination of strength and plasticity in high temperature. The original dendritic microstructure in the (CoCrFeNi)100-xGdx HEAs was completely fractured and transformed into a mass of deformed structures during thermal deformation. The mechanical properties at high temperature of the alloy system originate from the misorientation in the microstructure. Dislocation slip is the main deformation mechanism of the alloy system at high temperature. The coordinated deformation of the soft orientation for FCC phase and the hard orientation for HS phase affects the dislocation morphology in the microstructure. Dynamic recovery (DRV) plays a dominant role in the flow behavior of the alloy at high temperature, and work hardening is the main strengthening mechanism during plastic deformation. The correlation between microstructure evolution and mechanical properties of Gd alloyed CoCrFeNi HEAs during hot deformation has been established through comprehensive studies on deformation behavior.

Compressive Mechanical Properties and Energy Absorption of Cubic Spherical Hollow Cellular Material Based on the Rod and Curved Surface Structure

Cellular materials, such as lattices and honeycombs, were widely used for structural protection owing to their excellent mechanical properties. By combining the excellent characteristics of lattice and honeycomb curved surface structures, this study designed a cell called Cubic Spherical Hollow (CSH), which had the advantages of orthogonal isotropy and better spatial connectivity. Inspired by the micro-structural arrangement of bamboo fiber and conch shell, we designed the new CSH cellular materials through the interlayer offset strategy. Then, the effects of interlayer offset on the mechanical properties and compression deformation behavior were explored experimentally and simulatively. Compared with other cellular materials, CSH cellular materials exhibited excellent mechanical properties with higher specific strength and specific modulus. The arrangement offsets of the CSH cells between different layers led to a change in the deformation mechanism from a rod’s compressive mode to a combination of a rod’s compressive mode and curved surface’s bending mode. The initial peak stress and plateau stress decreased with the increased arrangement offsets of the CSH since the extruded protrusions of the structure filled the holes and reduced the lateral expansion behavior of the material in the pressurized environment. This phenomenon also reduced the transverse expansion and prevented the sudden change in stress in the constrained space, indicating that the structural deformation was stable and had excellent cushioning and energy absorption properties. In this study, the cellular material design strategy opens a new avenue for energy absorption.

Particle tracking-aided digital volume correlation for clay–sand soil mixtures

In this study, a novel, interdisciplinary method is introduced that merges fundamental geomechanics with computer vision to develop an advanced hybrid feature-aided digital volume correlation (DVC) technique. This technique is specifically engineered to measure and compute the full-field strain distribution in fine-grained soil mixtures. A clay–sand mixture specimen composed of quartz sand particles and kaolinite was created. Its mechanical properties and deformation behaviour were then tested using a mini-triaxial apparatus, combined with micro-focus X-ray computed tomography (μCT). The CT slices underwent image processing for denoising, segmentation of distinct phases, reconstruction of sand particles and feature extraction within the soil specimen. The proposed approach incorporated a two-step particle tracking method, which initially uses particle volume and surface area features to establish a preliminary matching list for a reference particle and then use the iterative closest point method for precise target particle matching. The soil specimen's initial displacement field was then mapped onto the DVC method's grid, and further refined through sub-voxel registration by way of a three-dimensional inverse compositional Gauss–Newton algorithm. The proposed method's effectiveness and efficiency were validated by accurately calculating the displacement and strain fields of the soil mixture sample, and comparing the results with those from a traditional DVC method. Given the soil's compositional and microstructural characteristics, these image-matching techniques can be integrated to create a versatile, efficient, and robust DVC system, suitable for a variety of soil mixture types.

Pioneering computational insights into the structural, magnetic, and thermoelectric properties of A3XN (A=Co, Fe; X=Cu, Zn) anti-perovskites for advanced material applications

This study pioneers the utilization of computer-controlled simulations to elucidate the structural, elastic, electronic, and thermoelectric properties of A3XN anti-perovskites (A = Co, Fe; X = Cu, Zn). Starting with the development of a detailed structural model, structural optimization calculations identify the stable Pm-3m cubic phase, aligning with experimental findings. Also, these optimizations indicate the ferromagnetic phase stability of A3XN anti-perovskites, further supported by positive Curie-Weiss constants of 60 K, 80 K, and 100 K for Co₃CuN, Co₃ZnN, and Fe₃CuN, respectively. The spin-dependent electronic properties, including band structure and density of states, are explored using multiple exchange-correlation (XC) functionals—GGA, GGA + U, and GGA + mBJ. The results uphold the metallic nature of the materials, accompanied by significant spin magnetic moments. Specifically, the calculated values of magnetic moments for Co3CuN, Co3ZnN, and Fe3CuN are 5.08 μB, 3.70 μB, and 7.61 μB, respectively. Furthermore, we compute the Curie temperatures for each compound, 942.48 K for Co3CuN, 692.7 K for Co3ZnN, and 1400.41 K for Fe3CuN, which are substantially elevated, indicating robust ferromagnetic behavior that persists well above ambient conditions. Mechanical properties, including stability, deformation behavior, and ductility, are validated through elastic calculations, with various mechanical anisotropy factors examined. From an application perspective, the thermoelectric characteristics of Co3CuN, Co3ZnN, and Fe3CuN are meticulously evaluated, focusing on parameters like the Seebeck coefficient, electrical conductivity, thermal conductivity, power factor and figure of merit (zT). The analysis highlights promising power factor values of 3.0×1011(W/cm.K2), 4.0×1011(W/cm.K2), and 6.0×1011(W/cm.K2) for Co3CuN, Co3ZnN, and Fe3CuN, respectively, suggesting potential for enhanced efficiency in thermopower generation, particularly in waste heat recovery applications. Furthermore, the study provides a comprehensive analysis of the ground-state optical properties of A3XN, including the dielectric constant, photoconductivity, reflectivity, refractive index, absorption coefficient, and extinction coefficient. The reflectivity spectra demonstrate high reflectivity of 45 % across visible and ultravioletregions, suggesting suitability for applications in coatings designed to mitigate solar heating effects.

Stress corrosion cracking performance of LPBF-built 316L stainless steel post-processed with heat treatment and severe shot peening

ABSTRACT This study investigated stress corrosion cracking (SCC) susceptibility in laser powder bed fusion (LPBF) printed 316L stainless steel under corrosive conditions. LPBF process inherently introduces residual stresses and surface defects that can compromise material integrity in aggressive environments. Post-processing techniques, specifically severe shot peening (SSP), heat treatments at 600°C and 900°C, and their combinations were employed to mitigate these issues. SCC testing in a boiling 25% NaCl solution assessed cracking over a period of five weeks. The results demonstrate that while SSP initially introduced compressive residual stresses potentially enhancing SCC resistance, subsequent mechanical deformation by U-bending diminished these benefits, leading to increased susceptibility to cracking. Tensile stresses induced by U-bending appeared to override the benefits of defect closure and reduced surface roughness, resulting in cracking. Notably, only specimens subjected to AB + SSP and HT600 + SSP conditions exhibited cracking during the testing period, highlighting the complex interplay between residual stresses, mechanical deformation, and SCC behaviour.

Influences of symmetric tilt grain boundary on the stretching deformation behaviors of Cu bicrystals

The microstructure of grain boundary (GB) becomes an important factor affecting the strength of nanomaterials during plastic deformation. In this work, Cu bicrystals with different coincidence site lattice (CSL) interfaces are constructed, and the influences of the symmetric tilt interface on the mechanical properties and plastic deformation behaviors during uniaxial tension are studied by molecular dynamics simulation. The results indicate that the peak stress of tensile stress-strain curves for most bicrystals is lower than its monocrystalline samples, except CSL3, CSL11 and CSL57 bicrystals with a continuous and single structural unit. The CSL3 bicrystal has the highest strength, while CSL33 bicrystal has the lowest strength among all the tested samples. The CSL11 and CSL57 bicrystals with a lower GB energy have a higher stability of interface, which delays the yielding. Moreover, the generation of twin and stair-rod dislocation at the interfaces strengthens the CSL11 and CSL57 bicrystals. The CSL3 almost has the same parameters as its monocrystalline sample S3, massive research has confirmed that the sample with a higher density twin (CSL3 interface) exhibits higher combined properties of strength and plasticity. This work may provide a guideline for GB engineering to improve material properties by controlling the GB structure.

Effect of grain size on the deformation mechanism and fracture behavior of a non-equiatomic CoCrNi alloy with low stacking fault energy

Manipulation of stacking fault energy (SFE) plays a significant role in microstructure control and in turn mechanical properties of advanced alloys. In this work, we present the influence of grain size on the mechanical properties and fracture behavior of a non-equiatomic CoCrNi alloy with low SFE. Specimens with controlled grain sizes ranging from 0.61 to 6.4 µm were fabricated through rolling and annealing. A novel SFs-dominated plastic deformation mechanism was discovered. Tensile strength decreases monotonically with increasing grain size, while ductility achieves a peak value at the medium grain size, contradicting with the typical behavior observed in most single-phase face-centered cubic (FCC) metallic materials deformed primarily by dislocation slips and/or twinning. The fracture behavior changes from void coalescence to quasi cleavage with grain coarsening, and the fracture mechanisms were analyzed. Additionally, the evolution of SFs and phase transformation is explored at various deformation strains.

Hydrogen-enhanced microbanding in an austenitic FeMnAlC low-density steel: Effect on hydrogen embrittlement resistance

We have investigated the influence of 101 mass ppm hydrogen content on the room temperature deformation structure and mechanical behavior of an austenitic Fe30Mn6.5Al0.3C (wt.%) low-density steel by several electron microscopy techniques, such as electron channeling contrast imaging (ECCI), electron backscatter diffraction (EBSD), and scanning transmission electron microscopy (STEM). The steel exhibits a high hydrogen embrittlement resistance associated with a moderated increase in strength (yield stress increase of 10%) and ductility (increase in the elongation to fracture of ∼ 8%). Analysis of the deformation structure reveals that hydrogen influences the deformation behavior by promoting deformation mechanisms associated with inhomogeneous plasticity (hydrogen-enhanced deformation banding (HEDB)) and strain localization (hydrogen-enhanced microbanding (HEMB)). These deformation mechanisms are ascribed to hydrogen-induced effects on dislocation plasticity, resulting in macroscopic kink bands, sub-micron localized strain gradients, and localized shear at cell blocks. We find that HEMB plays a relevant role in the deformation behavior of sub-micron localized strain gradients by promoting plastic relaxation and the enhanced storage of geometrically necessary dislocations within them. These effects mitigate the activation of damage mechanisms and enhance the strain-hardening capacity, contributing to the high HE resistance of the steel, comparable to that of high HE-resistant fcc alloys and steels.

Effect of Pore Size on the Mechanical Properties and Deformation Behavior of Porous ZrO2 (Y2O3) Ceramics Under Axial Compression

Effect of Pore Size on the Mechanical Properties and Deformation Behavior of Porous ZrO2 (Y2O3) Ceramics Under Axial Compression

An Assessment of the Mechanical Deformation Behavior of Three Different Clear Aligner Materials: A Digital Image Correlation Analysis

Introduction: The present study aimed to investigate the deformation behavior of three different clear aligner systems, CA® Pro+ Clear Aligner (Scheu Dental, Iserlohn, Germany), Taglus Premium (Taglus Company, Mumbai, India), and Spark Trugen (Ormco Corp., Orange, CA, USA), under compression testing, using the digital image correlation (DIC) technique. Materials and Methods: A total of 15 patients were treated with each of the three aligner systems, resulting in 45 sets of aligners. Each aligner set was fixed on the 3D-printed dental arches and then in an articulator. Then, the samples were subjected to occlusal forces using a purpose-built test stand to allow for controlled force application and precise displacement determination. The DIC technique was used for capturing the deformation behavior, providing detailed strain and displacement fields. Statistical analysis was performed using one-way ANOVA and Bonferroni post hoc tests with a significance of 0.05. Results: The results indicate that the Spark system exhibited the most substantial rigid displacement. Furthermore, the elastic deformation values of the Spark and Taglus systems were significantly higher than those of the CA Pro+ system (p &gt; 0.05). Conclusions: The Spark Trugen clear aligner system demonstrated a lower stability to rigid displacement and elastic deformation under compression testing compared to the Scheu CA® Pro+ Clear Aligner and Taglus Premium. All three tested clear aligner systems showed an increased resistance to elastic displacement and rigid deformation in the mandibular arch.

Mechanical properties and deformation behavior of a high entropy alloy with precipitate under cycle loading

Mechanical properties and deformation behavior of a high entropy alloy with precipitate under cycle loading

Mechanical properties and deformation behavior of Zr-based bulk metallic glass composites reinforced with tungsten fibers or tungsten powders

Mechanical properties and deformation behavior of Zr-based bulk metallic glass composites reinforced with tungsten fibers or tungsten powders

Effect of temperature on the nanoindentation behavior of monocrystalline silicon by molecular dynamics simulations

Monocrystalline silicon (Si) undergoes complex phase transformations under external loads, significantly affecting its performance and processing. In this study, molecular dynamics (MD) simulations are performed from 1 to 900 K to explore temperature effects on the mechanical properties and deformation behavior of monocrystalline silicon during nanoindentation. Results indicate that hardness and elastic modulus decrease with rising temperature. At lower temperature, the activation of plastic deformation is delayed. The suddenly release of stored elastic energy manifests as a pop-in event. The indentation creates a quadruple symmetric phase transformation zone, primarily consisting of Si-II at the core, flanked by Si-XIII and bct-5. Increasing temperature advances the plastic deformation of the sample. High temperatures facilitate the formation and subsequent phase transformation of Si-XIII, reduce the stability of bct-5 during unloading, and promote the amorphization of silicon. At high temperatures, the dislocation of silicon nucleates at the subsurface, resulting in the formation of a substable phase. The anisotropy of deformation is evident from the atomic perspective, based on the orientation dependence of the phase transformation. This research provides new insights into the deformation behavior and phase transformations of monocrystalline silicon, supporting manufacturing and application of silicon products.