Anisotropic Mechanical Properties Research Articles

Investigation on the crystal plasticity of α phase Ti-6Al-4V based on nano-indentation simulation and experiment

Ti-6Al-4V parts are usually hypothesized as isotropic mechanical properties during micro-machining operation. However, the crystal anisotropic mechanical property is an influential factor in the machining of crystals with different sizes and orientations. The hypothesis causes distinct variation in predicting machining force, and consequently the surface integrity cannot be exactly predicted in the micro-machining. Actually, Ti-6Al-4V parts are pseudo isotropy composed of grains with different orientations, elastic modulus, and hardness. Simultaneously, the initiation mode of plastic slip system varies with the grain orientation when the crystal is subjected to an applied load. It is challengeable to evaluate the effect of crystal orientation on its macroscopic properties, either by traditional experimental methods or macroscopic finite element analysis. Nano-indentation provides one novel method to investigate the plastic deformation of selected grains with specific orientations to characterize their mechanical response properties. This research aims to investigate the plastic behavior of α phase Ti-6Al-4V with different orientation grains by means of nano-indentation experiment and crystal plastic finite element method. In the study, single crystals of α phase are classified into “hard grains” (θ < 30°), “soft grains” (θ > 60°) and “normal grains” (30° < θ < 60°) by defining the crystal inclination angle (θ). The elastic modulus and hardness of hard grains are 9% and 28% larger than those of soft grains, respectively. This difference in mechanical properties depends on the slip system that dominates the plastic deformation behavior. The plastic deformation of soft grains is dominated by prismatic slip (48%), while hard grains are accommodated to plastic deformation by basal slip (51%). The average total cumulative shear strain of the soft grains is double that of the hard grains at a maximum load of 10 mN. Meanwhile, the sensitivity analysis is performed to evaluate the effects of the three sets of < a > slip systems and the two sets of < c + a > slip systems on plastic deformation with different grain orientations. The research contributes to the understanding of the plastic deformation mechanism in micro-machining and the exactly predicting the surface integrity generated from micro-machining.

Evaluating the influence of non-glide strain on prismatic dislocation in Mg using density functional theory calculations and the Peierls–Nabarro model

Mg and Mg alloys frequently exhibit anisotropic mechanical properties. Various high strength Mg alloys have been developed recently. Since the effect of non-glide stress on slip deformation can be prominent under a large strain or stress, it is crucial to examine the effect of non-glide stress/strain on dislocation motion. Mg easily undergoes 〈a〉 dislocation at ambient temperature; hence, in this study, the generalized stacking fault (GSF) energy of 〈a〉 dislocation on prismatic {101¯0} planes under non-glide strains was examined using the density function theory. To comprehend how dislocation behaves under various conditions, the relation between GSF energy and Peierls stress based on the discrete Peierls–Nabarro model was established, and screw and edge dislocation behaviors in the prismatic plane were discussed to obtain deeper understanding. While the dislocation core width decreases with compression and increases with tension, the Peierls stress increases greatly with compression and reduces slightly with the application of tension.

DFT Insights into MAX Phase Borides Hf2AB [A = S, Se, Te] in Comparison with MAX Phase Carbides Hf2AC [A = S, Se, Te

In this work, density functional theory (DFT)-based calculations were performed to compute the physical properties (structural stability, mechanical behavior, and electronic, thermodynamic, and optical properties) of synthesized MAX phases Hf2SB, Hf2SC, Hf2SeB, Hf2SeC, and Hf2TeB and the as-yet-undiscovered MAX carbide phase Hf2TeC. Calculations of formation energy, phonon dispersion curves, and elastic constants confirmed the stability of the aforementioned compounds, including the predicted Hf2TeC. The obtained values of lattice parameters, elastic constants, and elastic moduli of Hf2SB, Hf2SC, Hf2SeB, Hf2SeC, and Hf2TeB showed fair agreement with earlier studies, whereas the values of the aforementioned parameters for the predicted Hf2TeC exhibit a good consequence of B replacement by C. The anisotropic mechanical properties are exhibited by the considered MAX phases. The metallic nature and its anisotropic behavior were revealed by the electronic band structure and density of states. The analysis of the thermal properties-Debye temperature, melting temperature, minimum thermal conductivity, and Grüneisen parameter-confirmed that the carbide phases were more suited than the boride phases considered herein. The MAX phase's response to incoming photons further demonstrated that they were metallic. Their suitability for use as coating materials to prevent solar heating was demonstrated by the reflectivity spectra. Additionally, this study demonstrated the impact of B replacing C in the MAX phases.

An anisotropic conductive hydrogel for strain sensing and breath detection

Conductive hydrogels, with their excellent conductivity and flexibility, are highly suitable for use as strain sensors. However, they often exhibit weak mechanical properties and isotropy, which can limit their application potential. Moreover, the incorporation of self-powering capabilities within hydrogels would provide a significant advantage for sensor applications. In this study, we utilized hydrophilic delignified wood as a scaffold and impregnated it with FeCl3 solution to fabricate conductive wood. Subsequently, a precursor solution of polyvinyl alcohol (PVA), chitosan (CS), and 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPS) was prepared by heating and mixing. The conductive wood was then fully infiltrated with the precursor solution and transformed into a conductive wood-based hydrogel (CWH) using a freeze-thaw method. The aligned fibers in the conductive wood scaffold imparted anisotropic mechanical and electrical properties to the hydrogel, with a fracture stress anisotropy ratio of 47.5 (ratio of values parallel to the fiber direction to values perpendicular to the fiber direction) and an electrical conductivity anisotropy ratio of 1.55. The hydrogel remained soft after bonding with the wood scaffold, preserving its potential as a sensor. Experimental results demonstrated that the CWH sensor exhibited stable strain sensitivity (gauge factor of 0.2805 with R²=0.998 in the range of 0∼90°), enabling the monitoring of human joint bending and capturing facial smiles. The CWH also exhibited excellent resistance to expansion while maintaining high water content (79.4%), making it more suitable for use in humid environments compared to traditional hydrogels. Furthermore, we assembled the CWH into a humidity-driven generator and conducted power generation tests, revealing its promising power generation potential. The voltage significantly increased when exposed to humid air (from 6.2 mV to 66.1 mV). Lastly, we integrated the humidity-driven generator with a mask to create a breath detector, which was connected to an electrochemical workstation for testing. The test curve demonstrated the successful capture of orderly breathing activities from volunteers. The combination of these advantages positions CWH for a wide range of applications, including wearable flexible strain sensors, breath detection, bioelectrodes, and green energy generation devices.

Two-dimensional anisotropic monolayers NbOX2 (X = Cl, Br, I): Promising candidates for photocatalytic water splitting with high solar-to-hydrogen efficiency

Motivated by the recent experimental synthesis of two-dimensional (2D) NbOI2 which possesses a moderate bandgap and outstanding absorption of sunlight, using the first-principles calculations, we conduct a thorough study of the geometric configuration, electronic structures, and photocatalytic properties for NbOX2 (X = Cl, Br, I) monolayers. These NbOX2 monolayers have been demonstrated to be dynamically, thermally, and mechanically stable. The significant anisotropic mechanical properties of NbOX2 monolayers are reflected by the calculated Young's modulus and Poisson's ratio. Our results indicate that these NbOX2 materials unfold semiconductor characters with indirect bandgaps of 1.886, 1.909, and 1.813 eV, respectively. Among these monolayers, it is found that the NbOBr2 system exhibits a favorable photocatalytic activity in an acidic condition (pH = 0), and the NbOI2 monolayer can act as a potential photocatalyst for spontaneous photocatalytic water splitting under a neutral environment (pH = 7). Furthermore, the response of bandgap and band edge positions of NbOX2 monolayers to the exerting in-plane strain (–6% to 6%) are investigated. These NbOX2 monolayers also show strong light absorption from the visible to ultraviolet region and anisotropic high carrier transport. Particularly, the high solar-to-hydrogen efficiency of the NbOCl2 (1% tensile strain), NbOBr2, and NbOI2 monolayers are predicted to be 14.11% (pH = 0), 16.34% (pH = 0), and 17.05% (pH = 7), respectively. Therefore, we expect the NbOX2 monolayers to be promising candidates for highly efficient photocatalytic water splitting.

Use of Digital Image Correlation in Predicting Mechanical Properties of Parts Made by Additive Manufacturing

Abstract The publication is focused on the anisotropic properties of products of additive manufacturing using a Fused Filament Fabrication technology (FFF). Five different materials used in technical practice were tested. These materials are PLA (polylactic acid), PETG/CF (polyethylene terephthalate-glycol with carbon fibre, composite material), PETG (polyethylene terephthalate-glycol), ABS (acrylonitrile butadiene styrene), and ASA (acrylic styrene acrylonitrile). Mechanical properties are verified by tensile testing according to ASTM D638. Testing is complemented by a digital image correlation method to locate the areas with the highest load transfer. The results have shown clear anisotropic properties of the test specimens. Anisotropic mechanical properties were also confirmed by digital image correlation (DIC).

Thickness-Dependent Microstructure and its Effect on Anisotropic Mechanical Properties of Duplex Stainless Steel 2205 Multi-pass Welded Joints

Thickness-Dependent Microstructure and its Effect on Anisotropic Mechanical Properties of Duplex Stainless Steel 2205 Multi-pass Welded Joints

Mechanical Property and Microstructure of Rolled 7075 Alloy under Hot Compression with Different Original Grains

The hot compression of rolled 7075 alloys with different heat treatments was performed. The temperature ranged from 200 to 400 °C, and the strain rate was 0.01 s−1. The stress level decreases with the increasing temperature during compression, and the strength of the alloy in the original condition is higher than that of solution-treated (ST) alloy at the same deformation condition. The alloys with different heat treatments exhibit different anisotropic behaviors at 200 °C; the anisotropy for the alloys in both conditions becomes weaker with increasing temperature. Then, the corresponding microstructure was studied. The alloy’s microstructure in its original condition consists of fiber grains; however, many equiaxed grains are found after solution treatment due to the recrystallization. The grains with different shapes lead to different anisotropic mechanical properties. For the alloys in both conditions, the density of the dislocation decreases with increasing temperature during compression, and a certain number of subgrains were found when deformed at 400 °C due to the higher driving force and a higher rate of atomic migration. Meanwhile, it is observed that the precipitates of the alloy become coarser during higher-temperature deformation. Dynamic softening is dominant in high-temperature deformation, decreasing stress during hot deformation.

Anisotropy of mechanical properties and hardness homogeneity in the three orthogonal directions of a multi-directionally forged ZK60 Mg alloy

An extruded ZK60 Mg alloy was processed by multi-directional forging (MDF) for up to 9 passes at a temperature of 473 K. The microstructure, hardness homogeneity, texture, and mechanical properties of the alloy were examined on the transverse and longitudinal sections of the extruded and MDF-processed samples. Microstructural observations revealed that a fine-grained and homogeneous microstructure was achieved after 9 passes of MDF in all three mutually perpendicular planes (A, B, and C) of the processed billet. Mechanical properties were determined using the shear punch testing (SPT) method, and hardness homogeneity was studied by Vickers microhardness measurements. The ultimate shear strength (USS) decreased from 186.8 MPa in the as-extruded condition to 154.7 MPa after 3 MDF passes, due to the overcoming of texture softening to the strengthening by grain refinement. The ZK60 alloy showed anisotropic behavior in terms of USS and hardness, measured on the three A, B, and C planes after 3 and 6 MDF passes. The observed differences in the measured properties, however, almost vanished after 9 MDF passes because of homogeneity in the microstructure and texture. Vickers microhardness measurements revealed that the material has excellent uniformity in hardness throughout the billet after 9 MDF passes in all planes, due to a fully recrystallized homogeneous microstructure.

Towards Selective Laser Melting of High-Density Tungsten

Selective laser melting (SLM) of tungsten (W) is challenging due to its high melting point and brittleness, resulting in defects including balling phenomenon, porosity and cracks. In this work, high-density crack-free SLM W was fabricated by employing cost-effective powders modified through air jet milling. The influence of the SLM processing parameters on microstructure, density, crack formation and the resulting mechanical properties of SLM W was investigated. Laser energy density and hatch distance were found to be the most important parameters in controlling porosity and crack formation of SLM W. The check-like microstructure in horizontal plane was induced by the difference in thermal gradients, which were caused by the movement of the heat source between overlapping regions and central regions of the molten pool. Combined efforts including powder modification through air jet milling, a 67° rotation scanning strategy, a hatch distance of 0.08 mm and a laser speed of 450 mm/s result in dense crack-free SLM W with relative density of 99.3%, microhardness of 403 HV50, and bending strength of 154 MPa. Additionally, the microstructure changed upon annealing at 1200 °C, accompanied by the reduced anisotropy of mechanical properties on both horizontal and vertical plane.

Pseudo-anisotropic damage model of randomly oriented strands (ROS) for reproducing flexural damage behavior

We developed a pseudo-anisotropic damage model of randomly oriented strands (ROS) reinforced thermoplastic composites for reproducing flexural deformation and damage behavior by finite element analysis (FEA). The damage model applied stress triaxiality to capture the differences in the damage initiations among the tensile, compressive, and shear stress states. The damage model also included equivalent damage propagation function depending on the interlaminar shear property of ROS. The developed FE model was focused on the characteristics that ROS composites show macroscopic in-plane isotropic and out-of-plane anisotropic mechanical properties because of the laminated structure of ROS. Furthermore, all of the material parameters in the FE model were identified by performing simple deformation tests. As a result, the flexural numerical simulation could reproduce the experimental flexural deformation and damage behaviors of ROS plates with different thickness despite a complex stress state including in-plane and out-of-plane stresses. The developed FE model has potential to evaluate the safety of ROS-manufactured structural components. The evaluation of safety by FEA constructed in this study can improve the applicability of ROS composites.

H13 tool steel fabricated by wire arc additive manufacturing: Solidification mode, microstructure evolution mechanism and mechanical properties

The critical application value of AISI H13 tool steel in the die and mold industry and the great application potential of additive manufacturing (AM) technology in die manufacturing and repair have attracted extensive attention from researchers. However, there is no consensus on the solidification mode and microstructure evolution mechanism of H13 during AM. The relationship between the unique cellular/dendritic substructures and the grain structures in AM-fabricated H13 components has yet to be fully understood. This work focused on the microstructure and mechanical properties of different regions of the H13 component manufactured by wire arc additive manufacturing technology. Thermodynamic calculations and experimental results confirmed the formation of δ-ferrite during the non-equilibrium solidification of AM. The cellular/dendritic substructure is caused by the solidification of δ-ferrite and austenite together with the accompanying segregation. The results of optical microscopy and scanning electron microscopy, as well as the reconstructed prior austenite grain structure by electron backscatter diffraction (EBSD) all confirmed that the formation and distribution of cellular/dendritic substructures were not directly related to the prior austenite grain. The EBSD pole figures show that although the martensite transformation weakened the preferred orientation of crystals, the martensite phase in the typical structure of the deposition area still had a high texture strength, which may be the main reason for the anisotropic mechanical properties of the H13 component.

Fatigue crack growth in anisotropic aluminium sheets — phase-field modelling and experimental validation

Fatigue crack growth is decisive for the design of thin-walled structures such as fuselage shells of air planes. The cold rolling process, used to produce the aluminium sheets this structure is made of, leads to anisotropic mechanical properties. In this contribution, we simulate the fatigue crack growth with a phase-field model due to its superior ability to model arbitrary crack paths. A fatigue variable based on the Local Strain Approach describes the progressive weakening of the crack resistance. Anisotropy regarding the fracture toughness is included through a structural tensor in the crack surface density. The model is parameterised for an aluminium AA2024-T351 sheet material. Validation with a set of experiments shows that the fitted model can reproduce key characteristics of a growing fatigue crack, including crack path direction and growth rate, considering the rolling direction.

Comparison of printability and mechanical properties of rigid and flexible fiber-reinforced 3D printed cement-based materials

Since eco-friendly, labor-saving construction technologies are urgently needed than ever, concrete 3D printing technology has gained increasing attention. However, there are still limited studies focusing on reinforcement techniques for 3D printed cement-based materials (3DPCM) which restrict their applications. Herein, we revealed the differences between the influence of typical rigid and flexible fibers on the printability and mechanical properties of 3DPCM. Printability, including buildability and extrudability, was evaluated via fluidity and shape stability tests and verified by printing experiments. The anisotropy ratio was proposed to assess the anisotropic mechanical properties. Furthermore, the fracture energy and bend-press ratio were adopted to assess the toughness. Results indicate that steel, polypropylene (PP) and polyvinyl alcohol (PVA) fibers all increase the buildability but decrease the extrudability of 3DPCM. Compared to steel fibers, PP and PVA fibers have a greater impact on the printability owing to their entanglement. The alignment and wall effect of steel fiber drastically increase the anisotropy in the compressive strength of 3DPCM. PP fibers also intensify the anisotropy in the compressive strength due to their filling effect. Low content of steel fibers and PP fibers both have limited impacts on the toughness and the anisotropy in flexural strength of 3DPCM. The fracture energy of 3DPCM for the loading direction perpendicular to the interface is higher than that for the direction parallel to the interface. Contrary to PP fibers, samples with steel fibers have higher bend-press ratios once the loading direction is parallel to the interface.

Elastic and plastic mechanical properties of lithium measured by nanoindentation

Metallic lithium is the desired anode material for high energy density solid state batteries and shows a factor of four range in elastic modulus and two orders of magnitude difference in creep properties dependent on sample preparation and testing method. In this paper we use in-situ nanoindentation to measure the anisotropic mechanical properties from the BCC crystal structure and the effect of strain-rate and temperature, which have an impact on battery cycle performance. This work clarifies the reasons for the range of property values reported in the literature with a global equation for yield strength with strain-rate. From this information conclusions can be drawn around variables to optimise in order to minimise the required pressure for a chosen stripping critical current in solid state batteries.

Deformation effect of melt pool boundaries on the mechanical property anisotropy in the SLM AlSi10Mg

The effect of microstructure characteristic on the anisotropy of mechanical properties has been studied for a selective laser melt (SLM) AlSi10Mg material. The cell structure and fine grains at the melt pool boundaries (MPBs) are gradually eliminated by different heat treatment processes. Althought the cell structure of MPB has been eliminated, it is found that the mechanical properties of the transverse specimen and longitudinal specimen are still different due to the heterogeneity of grain. In the process of plastic deformation, when the tensile direction perpendicular to the MPB, the deformation incompatibility between fine grains and columnar grains lead to the excessive stress concentration and rapid fracture along the zone boundary. The change of loading direction can alleviate strain localization and improve the uniform deformation ability of the sample. The heterostructure of SLM AlSi10Mg is related to the remelting and resolidification of MPBs. The results provide guidance for the design of SLM AlSi10Mg material with better mechanical properties.

Selection and justification of drilling and blasting parameters using genetic algorithms

Purpose. Using experimental and theoretical studies to justify the rational location of charges of various types and their technological parameters in the fan, taking into account the physical and mechanical properties and structural features of the rocks in the mountain massif. Methodology. In the experiments, an improved method of geostructural analysis of rocks was used to obtain detailed data on their properties, the block structure of the massif, and the type and direction of development of crack systems. Identification of crack systems, their density, intensity, and direction of development of crack systems is carried out on petrographic sections using microscopic analysis, these are used to calculate the average indicator of the cracking coefficient, while the funneling method – the anisotropy coefficient. The justification of the rational location and the number of charges in each fan was performed using the methods of genetic algorithms and the developed software product. Findings. The coefficient of cracking and anisotropy of physical and mechanical properties of uranium ores was calculated, which was 78 cr/sm2 and 1.4, respectively. According to the developed mathematical models and the software product, the optimization problem was solved using genetic algorithms, which determined the main priorities: the location of the charge in the fan according to the structure of the massif and the rational diameter of the well, which helps to limit the number of oversized blocks of reflected ore. Originality. The regularities are established of the change in the anisotropy coefficient from the cracking coefficient, the nature of the distribution and the number of microcracks (cr/sm2) in the quartz grains, which is present in uranium ore according to a linear law, and the output (in %) of oversized blocks during the destruction of uranium ore from the cracking coefficient – according to the polynomial law. For the first time, the optimal location and the number of charges in each fan, the diameter of the wells, taking into account the type of rock, its strength and fissure, and the geometric parameters of the ore deposit, were determined based on the constructed mathematical models and the developed software product. Practical value. The indicated results of the experimental and theoretical studies will form the basis for the development and substantiation of rational parameters of resource-saving and seismically safe methods for breaking strong rocks of complex structure during the extraction of uranium and iron ores by the energy of the explosion in mines.

Grain size manipulation by wire laser direct energy deposition of 316L with ultrasonic assistance

The epitaxial growth of coarse and columnar grain structures along the build direction of additive manufactured metals is a usual phenomenon. As a result, as-built components often exhibit pronounced anisotropic mechanical properties, reduced ductility, and, hence, a high cracking susceptibility. To enhance the mechanical properties and processability of additive manufactured parts, the formation of equiaxed and fine grained structures is thought to be most beneficial. In this study, the potential of grain refinement by ultrasonic excitation of the melt pool during laser wire additive manufacturing has been investigated. An ultrasound system was developed and integrated in a laser wire deposition machine. AISI 316L steel was used as a substrate and feedstock material. A conversion of coarse, columnar grains (dm = 284.5 μm) into fine, equiaxed grains (dm = 130.4 μm) and a weakening of typical &amp;lt;100&amp;gt;-fiber texture with increasing amplitude were verified by means of light microscopy, scanning electron microscopy, and electron backscatter diffraction analysis. It was demonstrated that the degree of grain refinement could be controlled by the regulation of ultrasound amplitude. No significant changes in the dendritic structure have been observed. The combination of sonotrode/melt pool direct coupling and the laser wire deposition process represents a pioneering approach and promising strategy to investigate the influence of ultrasound on grain refinement and microstructural tailoring.

Unravelling anisotropic deformation behaviour of Ti-6Al-4V ELI fabricated by powder bed fusion additive manufacturing

The uniaxial compression tests with respect to the different loading directions (i.e., parallel, and perpendicular to the building direction) were performed to investigate the anisotropic deformation mechanism of Ti–6Al–4 V ELI (extra low interstitial) alloy fabricated by laser powder bed fusion (L-PBF). The tests showed anisotropic mechanical properties; the sample loaded perpendicular to the building direction (TDx) has a higher fracture strain and lower yield strength, but a superior hardening effect than those of the sample loaded along the building direction (BD). Electron backscatter diffraction (EBSD) and digital image correlation (DIC) analyses were conducted used at regions of interest (ROI) in as-built and deformed samples. The kernel average misorientation (KAM) analysis revealed that a trend of dislocation evolution is strikingly different according to the loading directions; uniform KAM distribution is observed in the BD sample, whilst localization at prior β grain boundaries is found in the TDx sample. In addition, it was identified via a microscopic strain distribution map that the unique layered microstructure (i.e., layer band) and prior β grain boundary are more sensitive to compressive loading than the surrounding matrix. The layer band and prior β grain boundary were formed with their directivity during the additive manufacturing process; thus, their morphology is different depending on the loading direction. As a result, the layer band and prior β grain boundary play a key role in anisotropic behaviour, more precisely, the anisotropic deformation behaviour originates from the morphology of the layer band and β grain boundary, which is changed with respect to the loading direction.

Moisture influence on anisotropic mechanical behavior of direct compounded compression molded PA6/Glass LFTs

Fibre-reinforced thermoplastics are ubiquitously present in structural engineering applications, making it essential to comprehensively understand their behavior under different environmental and loading conditions. The tensile and shear properties of a direct-compounded, compression-molded Polyamide 6 (PA6)/glass long fibre thermoplastic (LFT-D) material were investigated in this study. The effects of moisture on the anisotropic mechanical properties of PA6/Glass LFT materials were thoroughly examined by testing at four different material directions of 0°, +45°, ˗45°, and 90°. The results revealed that moisture content had a significant impact on the mechanical properties of PA6/Glass LFT materials. At a 2% moisture content, the material's behavior shifted from brittle to ductile under tension and shear loads. The presence of moisture reduced tensile strength and elastic modulus by up to 33% and 50%, respectively. Failure elongation increased by up to 323%, resulting in up to a 328% increase in tensile toughness. Furthermore, moisture content significantly decreased the shear modulus between 16% and 30%, and the ultimate shear strength between 13% and 29% in different material directions. The results attained in this study can aid in selecting the optimal application of PA6/Glass LFT for structures in many industries, including, but not limited to, automotive, aerospace, military, and marine industries, and serve as input for numerical modeling of these composite materials and model validation.