Anisotropic Tensile Behavior Research Articles

Enhanced quasi-isotropic ductility in bi-textured AZ91 Mg alloy processed by up-scaled RD-ECAP processing

In the present work, an up-scaled rotational die equal channel angular pressing (RD-ECAP), which circumvented the limitation of the removing and re-inserting procedure of the conventional ECAP, was developed to make it possible to prepare large scale ECAP billets with dimension of 50 mm × 50 mm × 100 mm, and was successfully applied to an as-cast AZ91 alloy without a prior thermomechanical treatment. Benefiting from the large scale ECAP billet, the anisotropic tensile behavior of the ECAP alloy was examined, and was carefully linked to its microstructure and texture evolution. Our results shown that the large scale AZ91 RD-ECAP alloy exhibited simultaneously improved strength and ductility compared to as-cast alloy, while it possessed significantly anisotropic mechanical behavior. Interestingly, the anisotropy of ductility was nonsignificant, showing dramatically enhanced quasi-isotropic ductility. The improved strength and ductility were ascribed to the significant grain refinement, fine second phase, and texture strengthening. The tensile anisotropy was resulted by the bi-texture which was comprised of four prismatic texture components and three basal texture components. This study clearly highlights the potential for scaling RD-ECAP for an industrial scale implementation, while significant anisotropic mechanic behavior should be paid much attention.

Anisotropic tensile behavior and related yield point phenomena in annealed ultrafine-grained pure aluminum

Abstract It is found that tensile flow curves of samples of annealed ultrafine-grained aluminum AA1090 show the development of a yield point and a significant mechanical anisotropy. To rationalize the anisotropic tensile behavior, the orientation data of the annealed material were measured using electron backscatter microscopy. It is found that the inferior mechanical properties of samples tested at 45° to the rolling direction may be attributed to a strong rolling texture effect and that the anisotropic magnitude of the yield drop may be related to the proportion of grains with soft orientations (defined as those with Schmid factor greater than 0.45) in the sample. Additionally, it is found that the anisotropy in tensile ductility is in general agreement with a Considere criterion analysis and that the mechanical anisotropy in the samples is only partly explained by the crystallographic texture, where microstructural anisotropy may also play a role.

Anisotropic tensile behavior of in situ precipitation strengthened Inconel 718 fabricated by additive manufacturing

This study investigated the microstructure and anisotropic mechanical properties of selective laser melting (SLM) processed Inconel 718 (IN718) component. In as-fabricated alloys, ultrafine columnar grained microstructure with highly dispersed precipitates γ" phases at grains boundary and even-distributed γ' phases inside the grains were observed. It was demonstrated that the as-fabricated longitudinal samples showed lower ultimate tensile strength (UTS) of 1101MPa but higher elongation of 24.5% compared to the transverse samples which showed UTS of 1167MPa and elongation of 21.5%. The excellent mechanical properties of both the longitudinal and transverse samples can be ascribed to the refined microstructure of the SLM material resulting from the high cooling rate imposed by laser processing. The anisotropy in strength and ductility was attributed to the {100} fiber texture and columnar grain morphology. The {100} fiber texture of columnar grains leads to high strength in transverse direction, while the columnar grain boundaries also served as a path along which damage can preferentially accumulate, leading to fracture.

Process-Structure-Property Relationships for 316L Stainless Steel Fabricated by Additive Manufacturing and Its Implication for Component Engineering

We investigate the process-structure-property relationships for 316L stainless steel prototyping utilizing 3-D laser engineered net shaping (LENS), a commercial direct energy deposition additive manufacturing process. The study concluded that the resultant physical metallurgy of 3-D LENS 316L prototypes is dictated by the interactive metallurgical reactions, during instantaneous powder feeding/melting, molten metal flow and liquid metal solidification. The study also showed 3-D LENS manufacturing is capable of building high strength and ductile 316L prototypes due to its fine cellular spacing from fast solidification cooling, and the well-fused epitaxial interfaces at metal flow trails and interpass boundaries. However, without further LENS process control and optimization, the deposits are vulnerable to localized hardness variation attributed to heterogeneous microstructure, i.e., the interpass heat-affected zone (HAZ) from repetitive thermal heating during successive layer depositions. Most significantly, the current deposits exhibit anisotropic tensile behavior, i.e., lower strain and/or premature interpass delamination parallel to build direction (axial). This anisotropic behavior is attributed to the presence of interpass HAZ, which coexists with flying feedstock inclusions and porosity from incomplete molten metal fusion. The current observations and findings contribute to the scientific basis for future process control and optimization necessary for material property control and defect mitigation.

Microstructure and anisotropic tensile behavior of laser additive manufactured TC21 titanium alloy

In the present work, two types of part with different geometries were fabricated by laser additive manufacturing (LAM) process under the same processing parameters. Tensile samples perpendicular to (horizontal) and parallel to (vertical) the build direction were produced after heat treated under different conditions. The results showed that the samples exhibit similar columnar β grains, but very different α phase characterizations. The tensile properties show significant anisotropic. The sample containing finest α laths shows highest ultimate tensile strength and yield strength. And the strength decreased with the increase of α laths width. The total elongation of the samples does not show regularity relationship with the strength. The horizontal samples show inferior ductility and brittle fracture due to the columnar β grain morphology and the presence of continuous grain boundary α layers. The coarse grain boundary α layers after double heat treatment further reduced the ductility. The vertical samples exhibit better ductility due to lack of continuous grain boundary α layers which perpendicular to the tensile load. The Vickers hardness test shows that the vertical samples were strengthened while the horizontal samples were little strengthened after tensile test.

Anisotropic tensile behavior of Ti–6Al–4V components fabricated with directed energy deposition additive manufacturing

The present work investigates the anisotropic mechanical properties of a Ti–6Al–4V three-dimensional cruciform component fabricated using a directed energy deposition additive manufacturing (AM) process. The mechanical properties of the component in longitudinal and transverse orientations with respect to the build layers were measured under uniaxial tension. While the average ultimate tensile strength of ∼1060MPa in both directions agrees well with prior studies on AM Ti–6Al–4V, the achieved elongations of 11% and 14% along the longitudinal and transverse directions, respectively, are higher. The enhanced ductility is partially attributed to the lack of pores present in these components. The anisotropy in ductility is attributed to the columnar prior-β grain morphology and the presence of grain boundary α, which serves as a path along which damage can preferentially accumulate, leading to fracture. In addition, the effect of oxygen on the strength and ductility of the component was studied. The findings indicate that a combined effect of an increase of 0.0124wt.% oxygen and a decrease in α-lath width due to differential cooling at different heights within the component resulted in an increase of ultimate and yield strengths without a significant loss of ductility. Furthermore, this study demonstrates that quasi-static uniaxial tensile mechanical properties similar to those of wrought Ti–6Al–4V can be produced in an AM component without the need for post-processing heat treatments.

Modeling of anisotropic tensile and cyclic viscoplastic behavior of a nickel-base directionally solidified superalloy

Effects of temperature and crystallographic orientation on tensile and cyclic viscoplastic behavior of a nickel-base directionally solidified superalloy, DZ125, have been experimentally investigated and modeled using a unified anisotropic viscoplastic constitutive model. This constitutive model is compiled as an ABAQUS/UMAT by the self-adaptive explicit integration scheme. A grouping optimization method is proposed to identify the material parameters. The results show that the unified viscoplastic constitutive model is able to characterize the rate-dependent anisotropic tensile and cyclic viscoplastic behavior of DZ125 superalloy and the simulation results are in good agreement with the experimental data.

Impact of material processing and deformation on cell morphology and mechanical behavior of polyurethane and nickel foams

The cell morphology and mechanical behavior of open-cell polyurethane and nickel foams are investigated by means of combined 3D X-ray micro-tomography and large scale finite element simulations. Our quantitative 3D image analysis and finite element simulations demonstrate that the strongly anisotropic tensile behavior of nickel foams is due to the cell anisotropy induced by the deformation of PU precursor during the electroplating and heat treatment stages of nickel foam processing. In situ tensile tests on PU foams reveal that the initial main elongation axis of the cells evolves from the foam sheet normal direction to the rolling direction of the coils. Finite element simulations of the hyperelastic behavior of PU foams based on real cell morphology confirm the observation that cell struts do not experience significant elongation after 0.15 tensile straining, thus pointing out alternative deformation mechanisms like complex strut junctions deformation. The plastic behavior and the anisotropy of nickel foams are then satisfactorily retrieved from finite element simulations on a volume element containing eight cells with a detailed mesh of all the hollow struts and junctions. The experimental and computational strategy is considered as a first step toward optimization of process parameters to tailor anisotropy of cell shape and mechanical behavior for applications in batteries or Diesel particulate filtering.

Anisotropic tensile properties of recovery annealed aluminum alloy sheet

Aluminum alloy sheets fabricated by direct chill cast (DC) and continuous cast (CC) routes were investigated. The aluminum sheet produced by heavy cold-rolling and recovery anneal exhibits highly anisotropic tensile properties, especially a rather poor ductility along the direction 45° from the rolling direction. The anisotropic tensile behavior has its origin in the rolling texture. The poor ductility in 45° direction could be attributed to flow localization associated with intense shear banding, which was triggered by the yielding phenomenon in DC specimens. For CC specimens, discontinuous yielding does not occur because of the presence of residual dislocations, and the problem of low ductility in 45° direction is less severe than that in DC specimens. For both DC and CC aluminum sheet, increasing strain rate could enhance the strength and also improve the ductility.

複合材料 甲虫上しの積層構造とその力学特性

It is well known that the structures of the organisms give some important hints for the material development. To obtain a new idea on the optimum design of the material structures, the fore-wing of Allomyrina dichotoma was used and its mechanical properties and micro structures were investigated. As a result, the non-equiangular laminated structure and mechanical anisotropy of A. dichotoma fore-wing were made clear. The fracture processes of the fore-wing could be classified into two types, and their fracture mechanisms depended on the average lamination angle of chitin fiber layers. The bridging chitin fibers could not be observed in type I, while they were observed in type II. It was found that the fore-wing had the anisotropic tensile behavior, and using a parameter, η, the anisotropic tensile behavior could be represented. The results obtained here should be helpful for the optimum material design.

Microtexture, micro structure and plastic anisotropy of AA2195

The anisotropic tensile behavior of a commercial lithium-containing aluminum alloy was studied in both rolled plate and extruded forms in solution-treated and quenched and T8 tempers. Microtexture and other electron microscopy techniques were used to correlate grain orientation and morphology, load direction and inhomogeneous plastic deformation in T8 material. The ratio of yield strengths between 45° and 0° test directions was the same for as-quenched and T8 material. The plate and extruded materials had strong Brass, 110〈112〉, textures. Pronounced slip bands were found in Brass oriented grains after 45° loading, on slip planes parallel to both the working direction and long axis of the grains; in a range from 0.02 to 20% average strain. An attempt to increase the area fraction of the T 1 precipitate variant on these planes had no effect on anisotropy. The intergranular fracture surfaces show coarse, linear features which suggest a connection between the planar slip bands and delamination fracture.

Pneumatic bursting characteristics of plastics films

AbstractThe bursting strength and inflated deflection of linear low density polyethylene (LLDPE), oriented polypropylene (OPP), flexible poly(vinyl chloride) (PVC), poly(ethylene terephthalate) (PET), and polyurethane (PUR) films of different thicknesses were investigated with the pneumatic bursting method. The study showed the bursting air pressure is directly proportional to the thickness of LLDPE, OPP, and PET films. The effect of different membrane diameters on the change of the bursting properties in OPP and PUR film was also investigated. The results showed that the bursting properties are inversely proportional to the membrane diameter. Furthermore, biaxial stress‐strain exerted on the pole region of the tested films was studied. The results denoted that the relationship between the biaxial and uniaxial tensile stress‐strain was considered for two types of film: (1) Film that presented an isotropic tensile behavior showed that the tangential stress‐strain is higher than the tensile stress‐strain. (2) Film that presented an anisotropic tensile behavior showed that the tangential stress‐strain is determined by the weaker tensile stress‐strain values between two directions.

The anisotropic behaviour of a preoriented poly (ethylene terephthalate) during plastic deformations

Data on the anisotropic tensile behavior of samples cut along several directions of a biaxially oriented PET sheet are here presented. Shear deformations were observed together with the usual elongations. The data are compared with the predictions of a non-linear model recently proposed.