Anisotropic Mechanical Properties Research Articles

Multiscale approach to determine the anisotropic mechanical properties of polyisocyanurate metal panels using FEM simulations

Building on previous publications, in this work an existing mesoscale simulation model was first extended to predict the non-linear anisotropic mechanical behavior of foam structures. Subsequently, a comparison between experimental and simulated data was performed to validate the selected simulation parameters. Here, good agreements were observed, especially for compressive loading. Based on these results, a multiscale approach was described in which the local foam properties were applied to macroscale models of PIR-based metal panels to predict the overall component properties. A further comparison of selected macroscopic experimental and simulated data also showed a good agreement. Due to the high computational and modeling effort, a sensitivity analysis was finally performed on the influence of the resolutions of the local mesoscale foam properties on the macroscopic metal panel properties. It was found that for the metal panels considered, it is sufficient to model the (almost) homogeneous core layer and outer edge areas with one layer each. These findings can also be applied to other metal panels with different thicknesses for future investigations, since it is known from previous investigations that the metal panels have qualitatively comparable property distributions.

Influence of micro-rolling on the strength and ductility of plasma-arc additively manufactured Ti–6Al–4V alloys

The aim of this study was to reduce the number of defects, refine the grain size, and improve the mechanical properties of Ti–6Al–4V. We investigated the effect of interpass micro-rolling on the microstructures and mechanical properties of Ti–6Al–4V alloys produced via plasma arc additive manufacturing (PAAM). The non-rolled plasma-arc additively manufactured (PAAMed) sample exhibited coarse columnar crystals, basket-weave microstructures, and Widmanstätten structures, while the interpass-micro-rolled PAAMed sample exhibited fine equiaxed crystals and basket-weave microstructures. Interpass micro-rolling could significantly reduce the number density and size of defects during PAAM, and the rolled samples exhibited lower mechanical property anisotropy than the non-rolled samples. Moreover, the rolled sample exhibited a higher yield strength (∼797.66 and 793.45 MPa), tensile strength (∼939.73 and 935.71 MPa), and elongation (∼12.83% and 14.73%) in the X- and Z-directions than the unrolled sample. These enhanced mechanical properties can be attributed to αGB fragmentation, grain boundary strengthening, dislocation strengthening, and a low crack density. The micro-cracks preferentially nucleated around defects in the non-rolled sample, resulting in high crack and defect densities.

Effects of rolling method on the microstructure and anisotropy of mechanical properties of Cu–15Cr in-situ composites

The effects of unidirectional rolling (UR) and cross rolling (CR) on the Cr phase morphology, texture, and anisotropy of mechanical properties of Cu–15Cr in situ composites were investigated by using optical microscope, x-ray diffraction, and quasi-static compression techniques. The results showed that the elongation of the Cr phase in the UR specimen (49.2 μm) was greater than that of the CR specimen (18.6 μm) in the rolling direction after rolling with a reduction of 86.7%, while the elongation of the Cr phase in the UR specimen (10.9 μm) was slightly lower than that of the CR specimen (11.7 μm) in the transverse direction. The volume fraction of the Goss texture component of the Cu matrix was the largest in the UR specimen (31.3%), while that of the Brass texture component was the largest in the CR specimen (28.0%). The approximate ∼ (102)[2‾2‾1] texture component (14.2%) was present in the CR specimen. The results of Sachs model calculations indicated that the anisotropy of the compressive yield strength of the CR specimen (10.8%) was greater than that of the UR specimen (6.8%) due to the difference in texture components. The critical stress required to cross the Cu/Cr phase interface was calculated and indicated that the presence of the fibrous Cr phase made the anisotropy of the compressive yield strength of the CR specimen (21.9%) lower than that of the UR specimen (32.7%). The difference in the anisotropy of the compressive yield strength of the two specimens was reduced by the competition between these two factors, and eventually, the anisotropy of the compressive yield strength of the UR specimen (17.7%) was slightly higher than that of the CR specimen (14.1%), indicating that the effect of the fibrous Cr phase on the compressive yield strength anisotropy was greater than that of the texture.

Prediction of the Anisotropy of Chiral Mechanical Metamaterials via Micropolar Modeling

Abstract The anisotropic elastic mechanical properties of a family of single material chiral mechanical metamaterials are explored systematically. An integrated monoclinic-micropolar constitutive model is developed to quantify the anisotropic mechanical properties of the chiral designs with different geometries. The model predictions are thoroughly verified by mechanical experiments on three-dimensional (3D) printed specimens and finite element simulations with periodic boundary conditions. The new integrated monoclinic-micropolar model can predict the anisotropic elastic properties in all directions. Normalized model parameters for this family of chiral designs are provided. Finally, the anisotropic effective stiffness and effective Poisson’s ratio of all geometric designs in this family are quantified. The anisotropy and the completeness of auxeticity are evaluated systematically.

Hybridization in wire arc additive manufacturing

Wire Arc Additive Manufacturing (WAAM) can produce a near-net shape of an object within a short period due to its capability of high deposition rate compared with other metal Additive Manufacturing (AM) processes. The recent developments in the WAAM have increased its efficiency and cost-effectiveness in producing viable products. However, poor surface quality, porosities, residual stresses, distortions, and anisotropic mechanical properties are a few inherent challenges still associated with the WAAM, which necessitates the hybridization of this process. Hybrid-WAAM is a synergic integration of one or more deposition processes, manufacturing processes, layering strategies, raw stock materials, and machine tool kinematics that are fully coupled and affect part quality, functionality, and process performance. This paper comprehensively reviews different levels of hybridization in the WAAM to eliminate its associated challenges. These levels of hybridizations are classified into five categories: hybrid-deposition processes, hybrid-manufacturing processes, hybrid-layering strategies, hybrid-machine tools, and hybrid-raw stock. Furthermore, these levels of hybridization are mapped to eliminate the associated defects/challenges in the WAAM, which will help the readers select an appropriate level of hybridization.

An overview of Mechanical properties of Nano-composites

Due to the anisotropic, heterogeneous structure, and advanced mechanical properties of these materials combined with the size effects in micromachining, micromachining of nanocomposites is thought to be a challenging operation. In terms of high cutting force, poor surface quality, and rapid tool wear, it results in worse machinability. The first of these two parts of this review paper will provide a thorough overview of the mechanical characteristics of diverse nanocomposites, while the second part will concentrate on the micro-machinability of these nanocomposite materials.

Effects of non-equilibrium microstructures on microstructure evolution and mechanical properties of laser powder bed fusion IN625 Ni-based superalloy during long-term thermal exposure at 700 °C and 750 °C

The effect of non-equilibrium microstructures on microstructure evolution and mechanical properties of laser powder bed fusion (LPBF) IN625 alloy during long-term thermal exposure at 700 °C and 750 °C was studied in this study. The as-built (AB) LPBF IN625 alloy had a typical non-equilibrium microstructure consisting of fine dendritic and cellular microstructures, Laves phase and high-density tangled dislocations. The non-equilibrium microstructure transformed into uniform recrystallized microstructure after solution treatment (ST). During long-term thermal exposure, δ phase in AB sample preferentially nucleated in inter-dendritic regions with high-density dislocations, while δ phase in ST specimen firstly nucleated at grain boundaries (GBs) and then grew into grains. The coarsening rate of δ phase in AB sample was lower and the size of δ phase was smaller than those in ST sample. The coarsening of Laves phase at GBs led to the depleted-δ zone in AB sample, which was not found in ST sample. For AB and ST samples, the ultimate tensile strength (UTS) and yield strength (YS) increased with the increase of thermal exposure time, while the elongation (EI) decreased. The tensile strength of AB sample was higher than that of ST sample during the thermal exposure at 700 °C, while their tensile strength was close during the thermal exposure at 750 °C. In addition, the anisotropy of mechanical properties of AB LPBF IN625 alloy was eliminated gradually during long-term thermal exposure. The microstructure evolution of LPBF IN625 alloy during long-term thermal exposure was explained by a newly proposed mold.

Correlation between microstructural heterogeneity and anisotropy of mechanical properties of laser powder bed fused CoCrFeMnNi high entropy alloy

The unique microstructure of face-centered-cubic (FCC) structured alloys fabricated by laser powder bed fusion (LPBF) contributes to outstanding mechanical performances, but inevitably leads to anisotropy of mechanical properties. In this study, the relationship between the hierarchical microstructure and mechanical properties along the horizontal, diagonal, and vertical directions of the LPBF-built CoCrFeMnNi high entropy alloy (HEA) were qualitatively and quantitatively investigated. The horizontal samples exhibit the highest yield strength (YS) and the lowest elongation, while the vertical samples show the lowest YS and a slightly lower elongation than the diagonal samples, which are nearly two times the horizontal samples. Among the microstructural features at multiple length scales, both the columnar grain morphology and texture determine the anisotropy of mechanical properties. For the first time, the volume-weighted (V–W) average grain size was used to estimate the YS and critical twinning stress (CTS) of the LPBF-built CoCrFeMnNi alloy with a complex grain size distribution. The V–W average grain size exhibited high accuracy in calculating the YSs of the diagonal and vertical samples as well as CTSs along all the three directions. For the horizontal sample, the grain morphology dominates over texture during deformation, which is the same for the diagonal and vertical samples at the early stage of deformation. The texture plays a more important role at the late stage of straining.

Microstructure, Mechanical Properties and Cross‐sectional Behaviour of Additively Manufactured Stainless Steel Cylindrical Shells

AbstractPowder bed fusion (PBF) is an additive manufacturing method that enables complex metallic components to be manufactured with high precision. The microstructure, mechanical properties and cross‐sectional behaviour of PBF additively manufactured stainless steel circular hollow sections are investigated through experiments in this paper, with a view to applications in construction. The experimental programme included tensile coupon tests, microstructural characterisation, initial geometric imperfection measurements and compression tests on PBF 316L stainless steel cylindrical shells with large diameter‐to‐thickness (D/t) ratios. Advanced measurement methods – 3D laser scanning and digital image correlation, were employed to measure the specimen geometries prior to testing and deformation fields during testing, respectively. The possible anisotropy in mechanical properties was examined through tensile coupon tests and correlated with the underlying microstructural and textural features. Compression tests were performed to investigate the resistance against local buckling of thin‐walled cylindrical shells produced by PBF. All cylindrical shells buckled below their yield loads with a chequerboard failure mode and revealed the anticipated trend of reducing capacity relative to the yield load with increasing local slenderness, reflecting the increasing susceptibility to local buckling.

Effect of heat treatment on microstructural heterogeneity and mechanical properties of maraging steel fabricated by wire arc additive manufacturing using 4% nitrogen shielding gas

In this paper, a maraging steel was fabricated by wire arc additive manufacturing (WAAM) using Ar 94% + O 2 2% + N 2 4% ternary mixture. The three thin-walls were studied as as-deposited, direct ageing, solid-solution ageing specimens, respectively. The evolution of microstructure, strengthening mechanism of nano-precipitates and the mechanical properties were systematically revealed. The results show that the microstructure of as-deposited sample is mainly composed of martensite, δ-ferrite and retained austenite. A small amount of martensite was reverted to austenite in aged specimens and δ-ferrite remained. A small number of ε‑copper particles precipitated on martensite lath owing to interlayer transient ageing in the as-deposited sample, and then grow up and disperse in the ageing sample. The Cr 2 N formed by the direct reaction of N and Cr atoms in the molten pool is dissolved after solid-solution. The heterogeneity of microstructure and preferential growth of texture result in large anisotropy of mechanical properties in as-deposited and ageing samples. Solid-solution heat treatment not only eliminates this anisotropy, but also greatly improves the elongation, which is attributed to the elimination of δ-ferrite in the microstructure. In addition, the twins of martensite lath formed during solution can enhance the strength of martensite but deteriorate its impact toughness to 42 J. • The strengthening mechanism of Cr2N and ε-Cu were systematically revealed. • The Cr 2 N is dissolved due to the diffusion of N atoms in the solid-solution process. • The twins of martensite laths enhance the strength of martensite but deteriorate its impact toughness. • The anisotropy of mechanical properties can be eliminated by solid-solution treatment.

A novel approach to mechanical characterization of pharmaceutical lyospheres

Lyosphere has been broadly used to deliver chemical and biotherapeutic entities. However, the fragile nature of lyospheres can result in challenges in operation, and there is no comprehensive understanding of its strength to resist directional stress. This research was aimed to develop an appropriate approach to comprehensively evaluate lyospheres' strength. An innovative method was developed to probe the shear strength of lyospheres employing a highly sensitive rheometer bundled with a bespoke 3D-printed holder. It is found that fracture energy could be considered as an appropriate descriptor for mechanical performance of lyospheres. At different RH, the strength of lyospheres was inversely proportional to the residual moisture content. Microstructure of lyospheres is found to be critical to explain the anisotropic mechanical properties. An aligned honeycomb-like structure was shown to directly correlate different fracturing-modes (buckling, collapsing and scissoring). The methods and results should provide insight for controlling lyospherical strength through formulation and processing. • An innovative mechanistic characterization was developed to study lyospheres. • Shear strength of fragile lyosphere is characterized for the first time. • The first report of humidity impact on mechanical properties of lyospheres. • Fracture-energy is identified as the best descriptor for the strength of lyospheres • An aligned honeycomb microstructure of lyospheres was revealed for the first time.

Hierarchical eutectic structure and superior mechanical property in low cobalt content AlCo0.2CrFeNi2.1 alloy by laser metal deposition

The fabrication of AlCo 0.2 CrFeNi 2.1 high entropy alloy via laser metal deposition (LMD) was motivated and implemented by the demand for overcoming the strength-ductility trade-off of the as-cast alloys due to the Co concentration. The microstructure features of AlCo 0.2 CrFeNi 2.1 alloy were characterized by scanning electron microscopy, X-ray diffraction, transmission electron microscopy, and electron back-scattered diffraction. The mechanical properties were evaluated by a tensile test at room temperature. The synergy of reduced Co content and LMD process led to the formation of hierarchical eutectic microstructures consisting of columnar grains, eutectic colonies, alternately arranged fcc(L1 2 )+B2 lamellae, and coherent Cr-rich nanoprecipitates in B2. The growth direction of those eutectic structures was found to be mainly parallel to the building direction (BD). The fcc(L1 2 )/B2 eutectics agreed well with the Kurdjumov–Sachs orientation relationship of {110} B2 //{111}L1 2 , and< 111 > B2 //< 110 >L1 2 . The LMD fabricated AlCo 0.2 CrFeNi 2.1 exhibited anisotropic mechanical properties when stretched in BD and transverse direction (TD). An excellent combination of the ultimate tensile strength (1246 MPa) and ductility (17.1%) was achieved in the BD, better than the as-cast counterpart. The elevated mechanical properties could be attributed to the high cooling rate solidification induced microstructural refinement. The same interlamellar spacing in BD and TD embraced a nearly equal ability to block dislocation movement and gave rise to the similar yield tensile strength. The differences in grain/colony size induced boundary strengthening in BD and TD were evaluated to account for the remarkable changes in ultimate tensile strength as well as ductility. • High entropy alloy AlCo 0.2 CrFeNi 2.1 was made by laser metal deposition(LMD). • Excellent combination of strength and ductility was achieved with less Co content. • LMD overrode chemical composition to affect strength-ductility trade-off. • Refined microstructure by LMD caused better property than casting. • Interlamellar spacing contributed to yield strength, grain/colony size affected ultimate strength.

Layer Orientation Effect on Fracture Mode and Acoustic Emission Characteristics of Continental Shale

Based on the Brazilian tests of continental shale with different layer orientations, combined with AE monitoring, the influence of layer orientation on the anisotropy of mechanical properties, fracture mode, and fracture mechanism of continental shale was analyzed. The results show that the tensile strength and deformation at the peak stress decrease with the increase of layer orientation at a constant deformation loading rate of 0.06mm/min, and the splitting modulus decreases first and then increases. The tensile strength was 90° &gt; 60° &gt; 45° &gt; 30° &gt; 0°, and the maximum and minimum tensile strengths were 5.154 MPa and 0.669 MPa, respectively. Under the action of splitting load, the samples with 30°, 45°, and 60° layer orientations mainly undergo shear failure along the layer orientation, while the samples with 0° and 90° layer orientations undergo tensile failure. In addition, the crack propagation in the 0° and 30° samples penetrated the bedding. These characteristics have important reference significance for the study of the mechanism of hydraulic fracture communication, propagation, and activation of structural planes.

X-ray computed tomography analysis of pore deformation in IN718 made with directed energy deposition via in-situ tensile testing

Directed energy deposition (DED) is a metal additive manufacturing technique often used for larger-scale components and part repair. It can result in material performance that differs from conventionally processed metal. This work studies spatial and orientation-based differences in tensile properties of nickel-based alloy IN718 using in-situ x-ray computed tomography to observe internal pore populations. Anisotropy and spatial variability in mechanical properties are shown while the evolution of pore shape during deformation is measured. Measured pore deformation is compared to predict deformations simulated using a computational crystal plasticity scheme, which provides insight, through inverse modeling, to the grain orientation in which the pore resides. The measurements provide a high fidelity method to compare experimental and computational approaches to pore deformation studies. Pore deformation measurements show that pores tend to grow and elongate in the direction of loading, consistent with ductile deformation and likely deforming with the material. Generally, the pore defects observed in this material (not from lack-of-fusion) do not cause so-called premature failure, and fully developed necking occurs prior to fracture.

Monolayer TiNI with Anisotropic Optical and Mechanical Properties

Anisotropic monolayer materials have always been investigated by physical researchers. In this paper, we report a stable two-dimensional TiNI monolayer with anisotropic mechanical, optical, and electrical conduction properties. By combining the methods of non-equilibrium Green’s function and density function theory, we obtain two-dimensional TiNI materials with mechanical, optical, and electronic transport properties that depend on the lattice orientation. In addition, the maximum Young’s modulus of the single-layer TiNI can reach 160 N/m2. The calculate result of electrical transport properties also indicates the anisotropic electron transport performance of TiNI monolayer. Moreover, the electron transport intensity along the direction b is about six times the conduction intensity along the direction a. The anisotropic mechanical and optical properties, as well as the tunable band gap and special electron transport characteristics, enable a promising future for monolayer TiNI materials in nano-optoelectronics.

On the Effect of Hot Rolling on Inclusion Size and Distribution in a Cast AISI 1070 Steel Railroad Wheel

The goal of this work is to examine the effect of hot deformation on shrinkage porosity and nonmetallic inclusions in an AISI 1070 grade steel industrially produced wheel casting. Steel cleanliness is an important consideration as it influences the mechanical properties of the final product. A high density of porosity and inclusions have been shown to be detrimental for mechanical properties, especially during hot rolling. Using a laboratory-scale rolling mill, cast preforms were subjected to a 66% cumulative reduction to determine the effect of thermomechanical processing on void closure and inclusions that may produce anisotropy in mechanical properties. Quantitative automated feature analysis, AFA, of inclusion type, size, morphology, and distribution was conducted utilizing an Aspex PICA 1020 scanning electron microscope to determine differences in inclusions and shrinkage porosity in the as-cast and as-rolled conditions. The results were compared with previously reported impact toughness values which indicated a trend with MnS projected length and average impact toughness in the T-L orientation. Reduction in shrinkage porosity was also verified utilizing 3D micro-X-ray CT scans. The AFA results showed a decrease in shrinkage porosity from 177 ppm in the as-cast condition to less than 35 ppm after rolling. Pores were in general much smaller and widely distributed after hot rolling and this would suggest improved impact properties. Analysis of nonmetallic inclusions revealed three primary categories of inclusions that included MnS, Al2O3, and complex inclusions that mainly consisted of MnS with an Al2O3 core, with small quantities of mixed silicates of Mn and Al and calcium aluminates (CaAl2O4).

Grain-scale material removal mechanisms of crystalline material micro-cutting

Crystalline material miniature parts are highly required under the development trend of miniaturization in some fields, and micro-cutting is a promising technology to manufacture complex-shaped crystalline material miniature parts. In the micro-cutting process of crystalline materials, the cutter edge radius, cutting parameters and grain size are in the same order of magnitude, and the workpiece has significant microstructure heterogeneity and mechanical property anisotropy. Therefore, the “cutter edge size effect” and “microstructure effect” occur during the micro-cutting process of crystalline materials, which make it difficult to predict the material deformation behavior and machinability, leading to low efficiency and poor accuracy in the manufacturing process of crystalline material miniature parts, and seriously restricting their widespread application. Taking Inconel-718 as the example, the influence of grain orientation, grain boundary and grain size on the micro-cutting machinability of crystalline materials are comprehensively investigated through single-crystal, bi-crystal and polycrystalline orthogonal micro-cutting simulations. Results show that, grain orientation affects the slip system and slip degree during micro-cutting processes, which leads to different material deformation behaviors. The influence of grain boundary on material behaviors in micro-cutting processes can be divided into two aspects i.e., the material response across grain boundary introduced by its presence and the response difference caused by the difference of grain boundaries. Grain boundary features like grain boundary misorientation angle, grain boundary interface orientation, the number deviation of primary slip systems and the Schmid factor deviation of primary slip systems significantly influence the micro-cutting machinability. Besides, grain size affects the micro-cutting machinability by influencing the number of grains, slip systems and grain boundaries involved in the affected zone. Clarified mechanisms can be used as a credible basis to predict the machinability of crystalline materials in micro-cutting processes, and improve the manufacturing efficiency and quality of crystalline material miniature parts.

Liquid Crystalline Polymer Coatings Fabricated by Initiated Chemical Vapor Deposition

AbstractLiquid crystalline polymer (LCP) coatings offer avenues for the fabrication of devices with smart surfaces incorporating responsive topography, reflectivity, or polarization from their unique anisotropic optical and mechanical properties. LCPs have most commonly been made by photopolymerization of reactive mesogens within confined cells. Here, an alternative method of preparing LCP coatings using initiated chemical vapor deposition (iCVD) is described. LCP‐iCVD copolymer coatings comprised of an acrylic cyanobiphenyl mesogenic monomer copolymerized with vinyl ether crosslinkers are prepared. Systematic experiments examine the relationship between the monomer properties, reactor conditions, and polymer deposition rate. The alignment of the mesogenic phase in the as‐synthesized coatings is also demonstrated to be controlled by the surface energy of the underlying substrate. Interestingly, the surface properties of LCP coatings measured by atomic force microscopy are shown to depend on the director orientation. The data presented in this work introduce mesogenic monomers into the library of vapor‐deposited polymer coatings.

Bayesian Inference With Gaussian Process Surrogates to Characterize Anisotropic Mechanical Properties of Skin From Suction Tests.

One of the intrinsic features of skin and other biological tissues is the high variation in the mechanical properties across individuals and different demographics. Mechanical characterization of skin is still a challenge because the need for subject-specific in vivo parameters prevents us from utilizing traditional methods, e.g., uniaxial tensile test. Suction devices have been suggested as the best candidate to acquire mechanical properties of skin noninvasively, but capturing anisotropic properties using a circular probe opening-which is the conventional suction device-is not possible. On the other hand, noncircular probe openings can drive different deformations with respect to fiber orientation and therefore could be used to characterize the anisotropic mechanics of skin noninvasively. We propose the use of elliptical probe openings and a methodology to solve the inverse problem of finding mechanical properties from suction measurements. The proposed probe is tested virtually by solving the forward problem of skin deformation by a finite element (FE) model. The forward problem is a function of the material parameters. In order to solve the inverse problem of determining skin properties from suction data, we use a Bayesian framework. The FE model is an expensive forward function, and is thus substituted with a Gaussian process metamodel to enable the Bayesian inference problem.

Coaxial laser metal wire deposition of Ti6Al4V alloy: process, microstructure and mechanical properties

Wire-based additive manufacturing (AM) shows a promising prospect in fabricating large-scale titanium aerospace components at a high deposition rate and low cost. The currently used wire-based AM processes commonly utilize a lateral feeding method with an acute angle to form a deposit, which reduces the flexibility and increases the difficulty of control in making complex components. In this work, a novel coaxial laser metal wire deposition (LMWD) process was used to fabricate the most widely used titanium alloy, Ti6Al4V. The coaxial wire feeding was achieved by a coaxial laser head through a vertically fed wire surrounded by an annular shape beam at focal plane. The surface quality, microstructure and mechanical properties of the deposited Ti6Al4V were examined. To show the characteristic of the coaxial LMWD process, conventional lateral LMWD was also conducted for comparison. The deposited Ti6Al4V wall showed a high surface quality and a microstructure with a mix of equiaxed β grains and columnar prior-β grains rather than coarse prior-β grains. The refined microstructure resulted in a low anisotropy in mechanical properties. The mechanism of the equiaxed β grains formation was also discussed. The combined effect of the reduced thermal gradient and the heterogeneous nucleation from the coaxial wire feeding played an important role in determining the refined microstructures in coaxial LMWD.