Stage Of Plastic Deformation Research Articles

Evaluation of thinning behaviour under the influence of plastic hardening and surface friction during small punch test

Understanding the deformation response of the material involving thinning under small punch loading is vital to ensure structural integrity. This paper systematically investigates the effects of plastic hardening on the thinning process under different levels of surface friction between the punch, die and specimen. The small punch test conditions are modeled using Finite Element (FE) software of Abaqus. An axisymmetric model with a bi-linear constitutive material model incorporating different plastic hardening slopes is employed. Furthermore, the Coulomb’s friction coefficient between the disc-shaped specimen and the punch as well as the die varies between 0 (frictionless) to 0.7. The study found that the effect of plastic hardening on thinning process is negligible. On the other hand, the effect of thinning at the center of the specimen is significant under frictionless surface conditions. Thinning is observed to be dominant during the membrane stretching and plastic instability deformation stages. As the surface friction increases, the resistance to sliding deformation decreases. As a result, tensile instability is predicted at the location offset from the center of the specimen. Future efforts to model material behaviour and determine mechanical properties using small punch load conditions must consider the effects of friction.

Study on dynamic response analysis and vibration control of TV tower under wind-rain load excitation

This study thoroughly examines the impact of the coupling effects of wind-rain load on the structural behavior of the television tower, and the effective vibration control method is employed to mitigate the dynamic response of the structure. A refined finite element model of the tower was developed, and the dynamic response characteristics of the structure under varying wind speeds and rain intensities are further investigated. Based on parameter analysis, the influence of mass ratio and frequency ratio on the damping efficiency of tuned mass damper (TMD) was revealed. The results demonstrate that compared to wind load alone, the node displacement increases more significantly near the top of the tower under wind-rain load. When the basic wind speed reaches 40 m/s, the TV tower will be damaged due to the extreme compressive stress of the 45 units on the compression side exceeding the yield strength of the members. Under extreme weather loads, the members on the compressive side at a height of 60 meters are most susceptible to yielding and entering the plastic deformation stage. The overall vibration reduction effectiveness of TMD increases with higher mass ratios, with a mass ratio of 1.5 % identified as optimal. Regarding the reduction of top displacement of the tower, the effectiveness of TMD varies with frequency ratio, showing an initial increase followed by a decrease; optimal vibration control is observed at a frequency ratio of 0.9.

Evaluation of Aeolian Sand Collapsibility Based on Physical Indicators in the Mu Us Desert, China

The collapsibility of aeolian sand has hindered the development of oil and gas resources and the construction of oil and gas stations in the Mu Us Desert. This study considered aeolian sand on the southern edge of the Mu Us Desert as the research object. Based on a water immersion load test, standard penetration test, and indoor geotechnical test, four evaluation indicators were selected, the water content, dry density, void ratio, and saturation. Combined with the support vector machine method, we established a method for evaluating the collapsibility of aeolian sand based on basic physical indicators. The results showed the following: (1) The degree of collapsibility was slight, with a small portion showing no collapsibility. And the load-settlement curve (P-s) was divided into three stages: the linear elastic deformation stage, the elastic–plastic deformation stage, and the collapsible deformation stage. (2) There was a strong relationship between the collapsibility coefficient and the four evaluation indicators for aeolian sand. Based on these indicators, we could accurately predict and evaluate the collapsibility coefficient. (3) Machine learning methods, such as the support vector machine, can effectively solve prediction and evaluation problems between variables when there is no clear mathematical relationship between multiple independent variables and a single dependent variable.

Microstructure-based simulation of constitutive behaviors in friction stir additive manufacturing

The Complex reheating phenomenon during friction stir additive manufacturing (FSAM) has a significant impact on the microstructural evolution. This, in turn, affects its mechanical properties. A flow stress model including the precipitate, solid solution and dislocation density evolution was proposed to reveal the relationship between the microstructure and constitutive behavior in FSAM of Al-Mg-Si alloys. The microstructure and mechanical properties of single-layer and multi-layer FSAM were investigated using experimental and numerical simulation methods. The results revealed that during the first reheating process, the precipitates exhibited dissolution and coarsening behavior in the heating stage. In the third reheating process, precipitates were generated during the heating stage because of the lower temperature. The multiple reheating process in FSAM promoted the generation of precipitates in the stirring zone. This phenomenon increased the yield strength from 183.46 MPa to 189.95 MPa. Meanwhile, the precipitate nucleation and growth during reheating process depleted the concentrations of Si and Mg in the matrix. A comparison of the stress-strain curves before and after the reheating process, revealed that the reheating process reduces the net flow stress in the plastic deformation stage. A decrease in the concentration of solid solution elements caused a decrease in the statistically stored dislocation density, and thereby, decreased the net flow stress.

Deliquescence of damaged rock salt under high humidity and its effect on inter-seasonal salt cavern gas storage

Salt cavern underground gas storages (UGSs) are ideal for mitigating demand fluctuations in gas resources such as hydrogen, helium, and natural gas. Rock salts surrounding the cavern are chronically exposed to high humidity during the inter-seasonal operation, and the effect of its deliquescence is worth investigating. In this study, deliquescence rates of damaged rock salt at the humidity of UGSs was measured. Undamaged rock salts deliquesce slowest. The rate increases by 532 % as the strain reaches 2.40 %. This ratio decreases to 372 % when rocks enter plastic deformation stages. Cracks and crystal defects in damaged rocks are inferred to accelerate deliquescence by increasing the local relative humidity through the Kelvin effect and lowering reaction energy barriers, respectively. As the crack widens with deformation, imbibed brine inhibits the deliquescence by healing defects and reducing water-salt contact. A subroutine coupling deformation and deliquescence of rock surrounding the cavern was developed. Its application in Jintan, China shows that deliquescence increases the cavern span, intensifying local creep and crack evolution. The volume shrinkage of the cavern increased by 2.80 %, and the safety factor was reduced, but empirical safety criteria were still satisfied. This study helps to assess UGS salt caverns' storage performance more accurately.

Study on temperature evolution law of coal containing gas under uniaxial loading process with different loading rates

AbstractIn order to investigate the evolution law of coal temperature during the gestation process of coal and gas outburst, laboratory experiments and numerical simulation approaches were employed. Infrared thermal radiation experiments on the surface of outburst coal during uniaxial loading and failure of coal were conducted. A coal and gas thermal‐hydromechanical coupling model considering the endothermic effect of desorption was established. Numerical simulation of uniaxial loading of gas‐containing coal was implemented to study the influences of deformation energy, frictional heat, and adsorption/desorption endothermic effects on coal temperature. The results indicate that the temperature of coal samples during the uniaxial loading and failure process generally exhibits a stepwise temperature increase. In the initial stage, the elastic thermal effect leads to a slow and fluctuating rise in the temperature of coal samples. During the yield and plastic deformation stages, frictional heat causes a rapid increase in the temperature of coal samples. With the increase of the loading rate, the increment of the temperature of coal samples gradually decreases and reaches the peak when the loading stress is 70% of the peak stress. According to the numerical calculation results, with the increase of the loading rate, the temperature reduction caused by gas desorption relatively decreases. By comparing the experimental results and numerical simulation results, it is found that the temperature reduction caused by desorption is greater than the temperature increments caused by deformation energy and frictional heat. The desorption endothermic effect and frictional heat effect are the dominant factors controlling the temperature variation of coal during the gestation process of outburst. The research achievements have significant theoretical significance and practical value for revealing the temperature evolution mechanism during the gestation process of coal and gas outburst, predicting coal and gas outburst, and protecting the atmospheric environment.

Multi-scale reservoir response characteristics of coalbed methane development through stress relief via horizontal well cavity completion in tectonically deformed coals

China’s coalbed methane (CBM) resources hold significant potential. However, the widespread presence of soft and low-permeability tectonically deformed coal (TDC) presents a challenge to the efficient development of CBM. The development of CBM through stress relief via horizontal well cavity completion (HWCC) offers a promising innovative solution to this problem. To elucidate the multi-scale reservoir response characteristics of CBM development through stress relief via HWCC in TDCs, this article comprehensively employs particle discrete element and finite element numerical simulation methods, and carries out the numerical simulation studies of cyclic seepage at the specimen scale, HWCC at the coal seam scale, and CBM development at the coal seam group scale. The main findings are summarized as follows. Unlike the stress-compression specimens, which exhibited overall failure, the differential distribution of pressure gradients within the specimens during the gas seepage experiments resulted in the development of microcracks concentrated at the bottom of the specimens. With the escalation of coal body structural damage, the permeability stress compression coefficient during the elastic deformation stage shows an increasing trend. Upon entering the plastic deformation stage, the specimen’s permeability shifts from a decreasing to an increasing trend. Increasing the lower limit pressure ratio, upper limit pressure ratio, and cycle rate of gas injection pressure could accelerate the failure efficiency of the specimens. Increasing the lower limit pressure ratio has a more pronounced effect on the TDC specimens, while increasing the upper limit pressure ratio has a more significant impact on the primary undeformed and cataclastic coal specimens. In TDCs, the phenomenon of wellbore collapse and cavity expansion becomes more pronounced. The cavity volume tends to increase with the increase in the initial well diameter, in-situ stress, and alternating bottom-hole pressure differences. The HWCC could enhances reservoir permeability and production in both the cavity completed and adjacent coal seams. For two horizontal wells with cavity completions in the same layer, excessively close well spacing is unfavorable for fostering inter-well interference and reservoir pressure drop. When the HWCC is applied to thin coal seams, the enhancement of permeability and production is limited. Reasonable optimization of drainage rates could effectively mitigate the reservoir permeability velocity-sensitive damage. The research findings extend related theories and provide a robust reference for subsequent practical engineering applications.

Fast Fourier transform approach to Strain Gradient Crystal Plasticity: Regularization of strain localization and size effect

The Strain Gradient Crystal Plasticity (SGCP) model, based on cumulative shear strain, is developed to regularize and simulate the size effect behavior of polycrystalline aggregates, specifically addressing the formation of localization bands, such as slip and kink bands, influenced by strain softening during the initial stages of plastic deformation. In this respect, the thermodynamically consistent derivation of the SGCP equations is presented, establishing their connection to the kinematics of classical crystal plasticity (CCP) framework. The governing balance equations are solved using the fixed-point algorithm of the fast Fourier transform (FFT)-homogenization method, involving explicit coupling between the classical and SGCP balance equations. To address this problem, a strong 21-voxel finite difference scheme is established. This scheme is considered to solve the higher order balance equation inherent to SGCP. Additionally, three types of interface conditions are implemented to explore the impact of grain boundaries on the transmission of localization bands. These conditions yield consistent intragranular/transgranular localization patterns in the MicroFree and MicroContinuity cases, while in the MicroHard condition all localization bands are intragranular with stress concentrations appearing at the grain boundaries.Analytical solutions corresponding to different material behaviors are developed and compared with numerical results to validate the numerical implementation of the FFT fixed-point algorithm. It is observed that both the macroscopic behavior and microscopic variables in CCP framework are highly influenced by grid resolutions (non-objective), leading to numerical instabilities arising from the material softening and subsequent formation of localization bands, both in single crystals and polycrystalline aggregates. Remarkably, the developed SGCP model provides results that are independent of grid resolutions (objective) and effectively regularizes the material behavior on local scale. Moreover, the non-local parameter of the model is capable of controlling the localization band widths. Finally, the proposed SGCP model, together with employed MicroHard condition on grain boundaries, is demonstrated to qualitatively reproduce main microstructural features of irradiated polycrystalline materials.

Study on Dynamic Mechanical Properties and Failure Pattern of Thin-Layered Schist

This paper studies the effect of schistosity on the dynamic mechanical properties and failure pattern of thin-layered schist. Wudang Group schist with thin layers is selected as the research object, and the influence of the dynamic mechanical properties and failure pattern of schist under different angles and spacing is studied by combining an SHPB test and numerical simulation. The results indicate that under dynamic loading, the stress–strain curve demonstrates elastic compression, plastic deformation, and strain softening stages. Moreover, it is observed that the dynamic critical failure strength of schist exhibits typical “U”-type strength anisotropy. Specimens with a schistosity angle of 0° or 90° exhibit higher dynamic compressive strength under dynamic loading, with axial splitting and schistosity splitting as predominant failure modes. Conversely, when the schistosity angles are 30°, 45° or 60°, there is a noticeable decrease in compressive strength accompanied predominantly by shear failure along with local compressive shear failure. We additionally noted that as the spacing between schists decreases from 22 mm to 7 mm, there is a gradual reduction in dynamic compressive strength by approximately 20.3%.

Characteristic of the changes in magnetic properties of heat-treated steel at the early stages of cold plastic deformation by tensile strain

The present work establishes alloy steel 38KhS exhibits distinct features such as an inflection point and a second peak in the field dependencies of differential magnetic susceptibility only in samples with ε = 4 % and tempering temperatures of 650 and 700 °C, unlike annealed low-carbon steel. The absence of such characteristics on the χd(H) curves for samples with ε = 2 % and Ttemp 650 °C is likely due to the high level of randomly distributed internal stresses remaining after heat treatment. These stresses prevent the formation of an «easy plane» magnetic texture after plastic deformation by stretching.

Synergistic densification mechanism of irregular Ti powder during CIP: 3D MPFEM simulation with real-shape particles

Achieving high green density is essential for ensuring the mechanical properties of powder metallurgy workpieces. However, the densification behavior of irregular ductile powders remains unclear due to oversimplification in current numerical simulations. To address this, a three-dimensional multi-particle finite element method model incorporating realistic powder morphology, size distribution, and stacking structure is constructed. It is found that a pivotal motion-deformation synergistic stage exists between the conventional particle rearrangement and elastic–plastic deformation stages. In this stage, plastic deformation is driven by the spheroidization of coarse powders, whereas the resulting vacancies in the stacking structure facilitate slight particle motion. Thereafter, plastic deformation is dominated by the flattening of fine particles, and the pore-filling capacity decreases due to the reduction in non-contact surface area. This synergistic and complementary interaction between the spheroidization of coarse powders and the flattening of fine powders enhances mechanical interlocking and promotes micropore closure. As a result, the micropores exhibit a tendency of downsizing and homogenization, substantially boosting the potential for achieving full densification during sintering. Based on these findings, a method for determining the optimal forming pressure is proposed, considering the manufacturing costs of powder compacts and the characteristics of the micropores in both green and sintered bodies.

The effects of pre-existing dislocations on the mechanical properties of iron

In atomistic simulations, pre-existing dislocations have been reported to reduce the yield stress compared to the ideal crystals. However, the underlying physics behind yield stress reduction is still unrevealed, which hammers the design of advanced materials. Here, large-scale molecular dynamics simulations are carried out to investigate the influence of pre-existing dislocations on the mechanical properties of body-centered cubic Fe crystals with dislocation, twinning, and phase transformation-dominated deformation mechanisms. The results suggest that the overestimated yield stress of all the crystals is significantly reduced by increasing dislocation numbers and obtaining closer flow stress on the uniform plastic deformation stage. This reduction in yield stress can be attributed to the lower thermo-dynamical driving force required to activate existing dislocations in pre-existing dislocation crystals than that to nucleating new dislocations in ideal crystals. Furthermore, pre-existing dislocations inhibited the phase transformation-dominated deformation process, but the twinning/dislocation-dominated deformation process still exhibited its original deformation mechanism.

Molecular dynamics simulations of thermomechanical properties of silicone-modified phenolic polymer

The silicone-phenolic multicomponent polymers are typically employed as the matrix of fiber-reinforced nanocomposites developed for reentry vehicles due to their excellent thermal and mechanical properties. The thermomechanical properties of the silicone-phenolic multicomponent polymer system, which are greatly related to the processing and microstructures, were studied using molecular dynamics (MD) simulations combined with experiments. A multistep dynamic polymerization approach was utilized to form the crosslinked polymer model, which was also validated in terms of both microstructures and properties. The thermomechanical properties of the crosslinked polymer system were established as a function of crosslinking degree, component ratio, temperature, strain rate, and cooling rate, and the influence mechanisms of the processing parameters were revealed. The crosslinking degree can greatly influence the glass transition temperature and volumetric coefficient of thermal expansion, which is attributed to the constrained chain mobility. The crosslinking degree and the component ratio have a significant effect on the morphologies and vibrational density of states of the polymer system, respectively, which in turn affects the thermal conductivity. The failure mode during uniaxial tensile was investigated in terms of the atomic energy distribution through MD simulations. The elastic and plastic deformation stages are dominated by intermolecular non-bonding interactions, but less contributed by the bonding interactions. This work can guide the design of polymeric nanocomposites by establishing the relationship of processing-microstructure-thermomechanical properties.

Study of Mechanical Properties of Different Hydrate Reservoirs

Based on the triaxial shear tests of mud sediments in the South China Sea, mud chalk-type sediments in the South China Sea, and sandy sediments in the Nankai Trough, Japan, at different hydrate saturation and enclosing pressures, the stress-strain relationships of hydrate-bearing clays, mud chalk-type soils, and sandy soils were analyzed. The test results show that:(1)The stress-strain curves of the South China Sea clay sediments show three stages of elasticity, plastic deformation and strain hardening, which are significantly different from those of the hydrate-free clays; the stress-strain relationships of the hydrate-containing clays before and after hydrate decomposition are significantly different, and the undrained strength of the clays decreases by up to 50% after hydrate decomposition compared with that before hydrate decomposition; the above results indicate that the presence of hydrate enhances the linkage or cementation between the clay particles. The above results indicate that the presence of hydrate enhances the linkage or cementation between the clay particles.(2)For the mechanical properties of the hydrate specimens of the muddy chalky sand type in the South China Sea, the hydrate endowment, effective stresses and pore pressures all have some influence on the strength and deformation properties. The inclusion of hydrate in the pore space enhances the shear expansion characteristics of the sediments. For the effect of effective stress on the mechanical properties of hydrate sediments, the increase of effective peritectic pressure reduces the strain softening properties of hydrate sediments. The destructive strength of the sediments increases with the increase of effective confining pressure.(3)For the hydrate specimens in the Nankai Trough of Japan under the same effective circumferential pressure conditions, with the increase of hydrate saturation, the stress-strain law of the sediments showed a tendency to transform from strain hardening to strain softening, and the morphology of sandy sediment axial strain-lateral strain curves was controlled by the factors of hydrate saturation, and the absolute value of the slope of the curves expressed the rule of change of the tangent Poisson's ratio.

Pyramidal dislocation driven martensitic nucleation: A step toward consilience of deformation scenario in fcc materials (II)

Dislocation glides and their interactions with other defects are central to our understanding of deformation mechanism enhancing plasticity and damage tolerance. Martensitic transformation (MT) is a fascinating phenomenon overcoming strength-elongation trade-off and thus tailoring structure-property architecture. However, dislocation plasticity of Fe-based hexagonal close-packed (hcp) martensite is still challenging due to its metastability, further complicated by controversies surrounding pyramidal dislocation even in pure hcp metals. To resolve the uncertainties, we address the pyramidal-dislocation-driven plasticity in Fe-based hcp martensite by employing in-situ transmission electron microscopy (TEM) and high-resolution (HR) annular bright field (ABF) imaging together with dislocation-contrast analyses. We show that the activation and dissociation of pyramidal dislocation govern the initial stage of plastic deformation, while subsequent cross-slip by the cooperative motion of dissociated pyramidal dislocations plays a key role in nucleation of new hcp martensite. By incorporating current dislocation model into previous models coupled with stacking-fault-energy concept, we propose a synthesized deformation scenario that offers a comprehensive perspective on plasticity and transformability.

Investigating infrared Radiation, Energy, and fracture evolution features of dry and wet coal under cyclic loading

The continuous mining activities at the working face cause periodic disturbances to the surrounding coal rock mass. Investigating the response characteristics of surface infrared radiation temperature, energy evolution features, and fracture development patterns in coal rock under cyclic loading and unloading is crucial for enhancing our understanding of the mechanisms of damage, degradation, and instability in rocks associated with mining operations. In this research work, we conducted infrared radiation observation experiments on both dry and wet coal samples subjected to uniaxial cyclic loading and unloading. Furthermore, we carried out a thorough analysis of the resulting temperature variations, energy changes, and fracture evolution patterns. It was found that the average infrared radiation temperature (AIRT) generally increases during the loading phase and decreases during the unloading phase, with the variance of successive minus infrared image temperature (VSMIT) exhibiting a sharp change just prior to failure. Energy analysis indicates that dissipated energy during the pore compaction and elastic deformation stages is minimal, while in the plastic deformation stage, the proportion of dissipated energy to total energy increases, displaying a “concave” upward trend. Additionally, fitting results show that the AIRT follows a single exponential decay relationship with dissipated energy, with wet coal exhibiting a greater decay coefficient, highlighting that moisture accelerates the rate of temperature decline. The Particle Flow Code (PFC) simulation results further demonstrate that the number of cracks in dry coal samples significantly exceeds that in wet coal samples, showing a single exponential relationship between the number of fractures and dissipated energy, which indicates that the development of fractures in dry coal rock occurs at a faster rate with increasing dissipated energy compared to wet coal rock.

Atomic-resolution investigations on dislocation-assisted evolution of {10[formula omitted]3} twin boundaries in a magnesium alloy

{101¯3}〈303‾2‾〉 twinning is usually activated at the later stage of plastic deformation of Mg alloys, which is closely relevant to their fracture behavior. Reactions between slip dislocations and twin boundaries (TBs) are suggested to facilitate TB migration, retarding the premature TB cracking. Here, dislocation-assisted evolution of {101¯3} TBs in a Mg alloy subjected to cyclic deformation were studied and modeled, according to transmission electron microscopy observations, theoretical analyses of interfacial defects, and molecular dynamics simulations. Atomic-resolution experimental observations showed that symmetric tilt grain boundaries (STGBs) near the {101¯3} twin orientation with steps were generated in the deformed Mg alloy. Theoretical analyses and atomistic simulations indicated that transformation of {101¯3} TBs into the STGBs could occur by reactions with incident basal 〈a60〉 dislocations in pairs from the twin and matrix respectively under the normal stress. STGB steps would be produced by reactions of individual basal 〈a60〉 dislocations with GB dislocations at the STGB. Importantly, resultant steps could further emit {101¯3} twinning dislocations to facilitate the STGB migration. Moreover, STGBs near the {101¯3} twin orientation could evolve back into {101¯3} TBs either by reactions with an array of basal 〈a60〉 dislocations, or by a GB sliding of b = 〈303‾2‾〉 theoretically. Our results may provide insights into the mechanisms of {101¯3} TB evolution in Mg alloys, which plays important roles in their plastic deformation and plasticity.

Void-induced mechanisms in tensile behavior of nickel-based single crystal superalloys

Void defects significantly impact the tensile properties of nickel-based single crystal superalloys. In this work, the dynamic response of void-included nickel-based single crystal superalloys under tensile loading was studied using molecular dynamics method. The effects of porosity and void size on the tensile behavior and the evolution of internal defects were explored from a microscopic perspective. The results indicate that the presence of voids promotes the development of internal dislocation defects and atomic phase transitions, especially in the initial stage of plastic deformation. The tensile strength decreases with increasing porosity. Plastic deformation and atomic phase transitions typically initiate between voids and continue until complete fracture, with shear strains and dislocation defects continuously concentrating around the voids. Notably, some HCP defect atoms distant from voids revert to FCC phase atoms during the tensile process, leading to a decrease in dislocation density. Additionally, the mode of fracture in the porous model is shear fracture, with shear strain and dislocation defects remaining at the fracture surface after complete fracture. The effects of void size on the tensile strength are relatively small. As the void size decreases, the shear strain bands in the models become more regular and the dislocation density decreases. However, the impact of small-sized voids on the material becomes increasingly evident with further stretching.

Simulation and Algorithmic Optimization of the Cutting Process for the Green Machining of PM Green Compacts.

Powder metallurgy (PM) technology is extensively employed in the manufacturing sector, yet its processing presents numerous challenges. To alleviate these difficulties, green machining of PM green compacts has emerged as an effective approach. The aim of this research is to explore the deformation features of green compacts and assess the impact of various machining parameters on the force of cutting. The cutting variables for compacts of PM green were modeled, and the cutting process was analyzed using Abaqus (2022) software. Subsequently, the orthogonal test ANOVA method was utilized to evaluate the significance of each parameter for the cutting force. Optimization of the machining parameters was then achieved through a genetic algorithm for neural network optimization. The investigation revealed that PM green compacts, which are brittle, undergo a plastic deformation stage during cutting and deviate from the traditional model for brittle materials. The findings indicate that cutting thickness exerts the most substantial influence on the cutting force, whereas the speed of cutting, the tool rake angle, and the radius of the rounded edge exert minimal influence. The optimal parameter combination for the cutting of PM green compacts was determined via a genetic algorithm for neural network optimization, yielding a cutting force of 174.998 N at a cutting thickness of 0.15 mm, a cutting speed of 20 m/min, a tool rake angle of 10°, and a radius of the rounded edge of 25 μm, with a discrepancy of 4.05% from the actual measurement.

Effect of subgrain microstructure on the mechanical properties of Invar 36 specimens prepared by laser powder bed fusion

Invar 36 samples were fabricated via laser powder bed fusion (LPBF) at various energy densities. In this work, a parameter range for the preparation of full-density Invar 36 samples was determined. The microstructural evolution and tensile properties of the materials were studied in the as-LPBFed state, and the role of subgrain structures on the fracture mechanism was investigated. According to the results of this analysis, as the energy density increased, the density first increased and then decreased. The maximum density (99.94 %) reached 65 J/mm3, and the simple density reached full density at 40–90 J/mm3. Due to constitutional supercooling, the microstructure of the alloy is composed of cellular subgrains and columnar subgrains. Columnar subgrains grow perpendicular to the boundary of the molten pool to the center of the molten pool, while cellular subgrains primarily exist in the remelting area of the molten pool. In the full density range, the ultimate tensile strength of the samples reaches 437–484 MPa, and differences in the morphology, distribution, and micronicomechanical properties of the subgrains are responsible for the differences in macroscopic properties. At 40, 65, and 90 J/mm3, the elastic moduli of the columnar subgrains are approximately 155.1 GPa, 161 GPa, and 162.4 GPa, respectively; the elastic moduli of the cellular subgrains are approximately 136.2 GPa, 140.2 GPa, and 139.9 GPa, respectively, which means that in the elastic deformation stage, the columnar subgrains are more resistant to elastic deformation; in the plastic deformation stage, different subgrains have different effects on crack propagation; the columnar subgrains grow perpendicularly to the melt pool boundary, which has a hindering effect on the extension of microcracks; and the cellular subgrains have a homogeneous grain size so that the microcracks can be easily extended along the cellular subgrain boundaries.