Anisotropic Tensile Properties Research Articles

Experimental Evaluation of Fatigue Behaviors and Tensile Properties of Selective Laser Melted K536 Alloy at Elevated Temperatures

Additive-manufacturing techniques show more and more utilization potentialities in today’s aviation industry. In order to ensure safe operation of additive-manufactured parts, it is important to have their mechanical properties well-characterized and assessed. In this study, elevated temperature fatigue behaviours and tensile properties of a selective laser melting (SLM) fabricated K536 alloy are investigated for horizontal and vertical building orientation, respectively. A series of tensile tests at 20 ºC ~700 ºC temperature range and stress-controlled fatigue tests at 400ºC and 600ºC are conducted. Effects of building orientation and temperature on tensile and fatigue behaviours are analysed. Scanning Electron Microscopy (SEM) is used to examine the fracture surfaces of fatigue specimens to qualify the failure mechanism and crack initiation sites. K536 parts manufactured via SLM are shown to exhibit anisotropic tensile properties at different testing temperatures. Anisotropy of fatigue properties is not obvious at 400ºC and 600ºC. Cracks are likely to initiate at the surface sliding or subsurface crystallographic plane of fatigue specimens in middle life regime and at subsurface or central zone crystallographic plane in longer life regime. In shorter life regime, cracks are easy to initiate at un-melted zones of fatigue specimens.

Augmented repair of radial meniscus tear with biomimetic electrospun scaffold: an in vitro mechanical analysis.

BackgroundLarge radial tears that disrupt the circumferential fibers of the meniscus are associated with reduced meniscal function and increased risk of joint degeneration. Electrospun fibrous scaffolds can mimic the topography and mechanics of fibrocartilaginous tissues and simultaneously serve as carriers of cells and growth factors, yet their incorporation into clinically relevant suture repair techniques for radial meniscus tears is unexplored. The purposes of this study were to (1) evaluate the effect of fiber orientation on the tensile properties and suture-retention strength of multilayered electrospun scaffolds and (2) determine the mechanical effects of scaffold inclusion within a surgical repair of a simulated radial meniscal tear. The experimental hypothesis was that augmentation with a multilayered scaffold would not compromise the strength of the repair.MethodsThree multilayered electrospun scaffolds with different fiber orientations were fabricated–aligned, random, and biomimetic. The biomimetic scaffold was comprised of four layers in the following order (deep to superficial)–aligned longitudinal, aligned transverse, aligned longitudinal, and random–respectively corresponding to circumferential, radial, circumferential, and superficial collagen fibers of the native meniscus. Material properties (i.e., ultimate stress, modulus, etc.) of the scaffolds were determined in the parallel and perpendicular directions, as was suture retention strength. Complete radial tears of lateral bovine meniscus explants were repaired with a double horizontal mattress suture technique, with or without inclusion of the biomimetic scaffold sheath. Both repair groups, as well as native controls, were cyclically loaded between 5 and 20 N for 500 cycles and then loaded to failure. Clamp-to-clamp distance (i.e., residual elongation) was measured following various cycles. Ultimate load, ultimate elongation, and stiffness, were also determined. Group differences were evaluated by one-way ANOVA or Student’s t-test where appropriate.ResultsAligned scaffolds possessed the most anisotropic mechanical properties, whereas random scaffolds showed uniform properties in the parallel and perpendicular directions. In comparison, the biomimetic scaffold possessed moduli in the parallel (68.7 ± 14.7 MPa) and perpendicular (39.4 ± 11.6 MPa) directions that respectively approximate the reported circumferential and radial tensile properties of native menisci. The ultimate suture retention load of the biomimetic scaffold in the parallel direction (7.2 ± 1.6 N) was significantly higher than all other conditions (p < 0.001). Biomimetic scaffold augmentation did not compromise mechanical properties when compared against suture repair in terms of residual elongation after 500 cycles (scaffold: 5.05 ± 0.89 mm vs. repair: 4.78 ± 1.24 mm), ultimate failure load (137.1 ± 31.0 N vs. 124.4 ± 21.4 N), ultimate elongation (12.09 ± 5.89 mm vs. 10.14 ± 4.61 mm), and stiffness (20.8 ± 3.6 vs. 18.4 ± 4.7 N/mm).ConclusionsWhile multilayered scaffold sheets were successfully fabricated to mimic the ultrastructure and anisotropic tensile properties of native menisci, improvements in suture retention strength or adoption of superior surgical techniques will be needed to further enhance the mechanical strength of repairs of radial meniscal tears.

Biomimetic jellyfish-like PVA/graphene oxide nanocomposite hydrogels with anisotropic and pH-responsive mechanical properties

Jellyfish mesogloea with a well-developed anisotropic microstructure exhibits excellent and pH-responsive mechanical properties. It remains a great challenge to fabricate hydrogels mimicking the hierarchical structures and intriguing properties of biological hydrogels. Here we report the fabrication of a biomimetic jellyfish-like polyvinyl alcohol/graphene oxide (PVA/GO) nanocomposite hydrogel through a convenient and effective directional freezing–thawing technique. The resulting hydrogels show microstructures, water contents, and mechanical properties very similar to those of jellyfish mesogloea. Free-standing PVA/GO hydrogels with extremely high water contents (97–99 wt%) are obtained. The hydrogels show anisotropic porous structures consisted of microsized fibers and lamellae. The hydrogels exhibit high tensile and compressive strengths, up to 0.17 MPa and more than 2 MPa, respectively. In addition, anisotropic tensile mechanical properties are also observed. More interestingly, the PVA/GO nanocomposite hydrogels exhibit pH-responsive mechanical properties, which become weaker when swollen in acidic and basic solutions. Jellyfish-like structure that can mimic the swimming style of jellyfish is constructed with the PVA/GO nanocomposite hydrogel. This study might provide new idea for designing and fabricating novel biological or bio-inspired hydrogels for various applications in biomedical, industrial, and soft robotics fields.

Decarburization of stainless steel during selective laser melting and its influence on Young's modulus, hardness and tensile strength

Stainless steel was investigated in terms of the evolution mechanism of chemical elements during selective laser melting. It was found that 21% carbon was lost and the decarburization occurred. The carbon-gradient structure contributes to a low Young's Modulus and hardness in molten pool boundary and also anisotropic tensile properties.

Induction of fiber alignment and mechanical anisotropy in tissue engineered menisci with mechanical anchoring

This study investigated the effect of mechanical anchoring on the development of fiber organization and anisotropy in anatomically shaped tissue engineered menisci. Bovine meniscal fibrochondrocytes were mixed with collagen and injected into molds designed to produce meniscus implants with 12mm extensions at each horn. After a day of static culture, 10 and 20mg/ml collagen menisci were either clamped or unclamped and cultured for up to 8 weeks. Clamped menisci were anchored in culture trays throughout culture to mimic the native meniscus horn attachment sites, restrict contraction circumferentially, and encourage circumferential alignment. Clamped menisci retained their size and shape, and by 8 weeks developed circumferential and radial fiber organization that resembled native meniscus. Clamping also increased collagen accumulation and improved mechanical properties compared to unclamped menisci. Enhanced organization in clamped menisci was further reflected in the development of anisotropic tensile properties, with 2–3 fold higher circumferential moduli compared to radial moduli, a similar ratio to native meniscus. Ten and 20mg/ml clamped menisci had similar levels of organization, with 20mg/ml menisci producing larger diameter fibers and significantly better mechanical properties. Collectively, these data demonstrate the benefit of using bio-inspired mechanical boundary conditions to drive the formation of a highly organized collagen fiber network.

Anisotropic tensile properties of tungsten fiber reinforced Zr based metallic glass composites

Abstract The tensile properties and deformation behaviors of Zr based metallic glass composites containing different tungsten fiber orientations were investigated. The angles (θf) between tungsten fiber orientation and loading axial direction are 0°, 15°, 30°, 45°, 60°, 75° and 90°, respectively. The results show that the strength and the failure modes vary with θf. The tensile strength of the composite decreases as the θf increases. The tensile strength of the composite at θf=90° is only 253 MPa. The plasticity of all the composites do not be improved. The composites failed approximately 90° normal fault at θf=0°/15°, while the composites failed along the tungsten fiber when the θf is bigger than or equal to 30° because of the low axial grain boundary strength of the elongated W grains.

Physical properties of biaxially oriented PA6 film for simultaneous stretching and sequential processing

Abstract There are two different stretching processes that produce the biaxially oriented film, namely the tenter process and double bubble tubular film process. Furthermore, there are two tenter processes, i.e., the sequential biaxial stretching process and simultaneous biaxial stretching process. There is no report describing the difference among film physical properties of the three different processes. The biaxially oriented polyamide film using the double bubble tubular process has good balanced physical property and high impact strength, thus it is used for proper applications utilizing their advantage properties. In this report, the influence of each biaxial stretching process on film physical properties of polyamide, which has hydrogen bond, was studied in detail. As a result, the tentering process film has anisotropic tensile properties between machine direction (MD) and transverse direction (TD). This result was influenced by a later stretching process, namely TD stretching. On the contrary, the double bubble tubular film has good balanced properties, especially thermal shrinkage and impact strength. Tentering simultaneous stretching film has much larger shrinkage in MD than in TD. The sequential stretching film has larger shrinkage in TD than in MD. The double bubble tubular film has high impact strength, because it corresponds to the balanced molecular orientation.

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.

Nonlinear and anisotropic tensile properties of graft materials used in soft tissue applications

Background The mechanical properties of extracellular matrix grafts that are intended to augment or replace soft tissues should be comparable to the native tissue. Such grafts are often used in fiber-reinforced tissue applications that undergo multi-axial loading and therefore knowledge of the anisotropic and nonlinear properties are needed, including the moduli and Poisson’s ratio in two orthogonal directions within the plane of the graft. The objective of this study was to measure the tensile mechanical properties of several marketed grafts: Alloderm, Restore, CuffPatch, and OrthADAPT. Methods The degree of anisotropy and non-linearity within each graft was evaluated from uniaxial tensile tests and compared to their native tissue. Findings The Alloderm graft was anisotropic in both the toe- and linear-region of the stress–strain response, was highly nonlinear, and generally had low properties. The Restore and CuffPatch grafts had similar stress–strain responses, were largely isotropic, had a linear-region modulus of 18 MPa, and were nonlinear. OrthADAPT was anisotropic in the linear-region (131 MPA vs 47 MPa in the toe-region) and was highly nonlinear. The Poisson ratio for all grafts was between 0.4 and 0.7, except for the parallel orientation of Restore which was greater than 1.0. Interpretation Having an informed understanding of how the available grafts perform mechanically will allow for better assessment by the physician for which graft to apply depending upon its application.

Measuring Technology of the Anisotropic Tensile Properties of Woven Fabrics

A new creditable and effective multi-axial circular tensile tester (MACTT) with 16 load sensors installed around a circumference has been developed. The new tester could be used to measure tensile properties in various directions with one sample simultaneously under the same initial conditions. As a result, not only an error could be reduced, but also the experiment samples and time could be saved. The experimental results showed good agreement with the theoretical approximate values calculated based on Hooke's Law. We also compared the stress distributions obtained by the new tester with those tested by the Kawabata's Evaluation System (KES) instrument and the results confirmed that the new tester was theoretically reasonable and practically feasible for measuring orthotropic tensile properties of the fabrics with symmetrical structures, and that the new tester could also be used to test and evaluate the anisotropic tensile properties of fabrics with no orthogonal main axes.

Drawing Forces and Film Properties in Semi-Sequentially Stretched Polypropylene

The relationship between biaxial stretching and oriented polypropylene film properties is studied. Initial films have been made with a 6×6 areal draw ratio (ADR) while reducing the transverse direction (TD) drawing speed and maintaining the machine direction (MD) speed. Slowing the TD speed increases the final TD drawing force and produces anisotropic film shrinkage. Varying the draw ratios in both directions creates anisotropic tensile properties. By changing both drawing speeds and draw ratios, films with similar shrinkage but differing tensile properties have been made.

Anisotropic Tensile Properties at Room and Elevated Temperatures in Warm-Extruded AZ61 Magnesium Alloy

The texture characteristics and the relationship between texture and tensile properties at room temperature and superplasticity at high temperatures in a hot extruded AZ61 alloy are examined in this paper. After warm extrusion, the alloy exhibits a of refined grains microstructure and a sharp basal {0001} texture. The tensile properties at room and elevated temperatures in extruded with the loading axis oriented at 0°, 45° and 90° to the extrusion direction are tested. It is found that the 45° specimens exhibit has lower yield strength and higher ductility. The possible causes for mechanical anisotropy are also analyzed based on the Schmid factor calculations.

Effect of texture evolution on tensile properties of Al–Ni eutectic alloy fabricated by equal channel angular pressing

The present study investigated in detail the effect of texture evolution on the mechanical properties of an Al–5·7 wt-%Ni eutectic alloy, which was subjected to severe plastic deformation by the equal channel angular pressing (ECAP) technique. The ECAP procedure was carried out using two strain introduction methods, route BC and route A, at a temperature of 298 K and a pressing rate of 0·33 mm s−1. The as pressed microstructures were observed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Results indicated that the Al–Ni eutectic alloy specimens after ECAP processing by route BC and route A methods had very different microstructures, which strongly affected the tensile properties of the specimens. It was demonstrated that after ECAP processing by route BC, fine Al3Ni particles of ∼300 nm were homogeneously dispersed in the aluminium matrix, and the specimens showed no clear anisotropy in tensile properties. After ECAP processing by route A, however, eutectic textures containing α-Al and Al3Ni fibrous dispersoids had a highly anisotropic distribution and were demonstrated to have significantly anisotropic tensile properties. Based on the experimental results, the fracture mechanism during tensile testing of the Al–Ni eutectic alloy using different strain induction methods is discussed.

A study of texture and temperature dependence of mechanical properties in hot rolled Ti–25Al– xNb alloys

A two-stage rolling process at 900 °C has introduced a mixture of textures consisting of basal and non-basal texture components in Ti–25Al– xNb ( x=7, 10, 13) alloys. The basal texture components are (0 0 0 2)〈 2 0 2 ̄ 0 〉, (0 0 0 2)〈 1 1 2 ̄ 0 〉 and (0 0 0 2)〈 4 3 ̄ 1 0 〉, while the non-basal texture components are (0 1 1 ̄ 5) [ 2 ̄ 1 1 0 ] and ( 0 1 1 ̄ 6 )[ 0 3 ̄ 3 1 ]. The texture measurement was carried out on the sheet specimens using X-ray diffraction (XRD) by measuring six incomplete pole figures. It shows the degree of the basal texture of the Ti–25Al– xNb alloys decreases as the Nb content of the alloy increases. The textured alloy specimens present the anisotropic tensile properties. The degree of anisotropy is evaluated by the anisotropic index δ, which indicates that the degree of anisotropy reduces slightly with the increase of the deformation temperature.

加熱鋳型式連続鋳造法で作製したＡｌ‐Ａｌ３Ｎｉ一方向凝固材の冷間圧延と機械的性質

Cold rolling and mechanical properties of unidirectionally solidified Al–Al3Ni strip produced by an open type, horizontal, heated mold continuous casting process were investigated. As-cast and heat-treated strips were used as starting materials for cold rolling. Cold rolling was done in two ways in which the rolling direction is parallel and perpendicular to the casting direction, i.e., the longitudinal direction of Al3Ni fiber. Edge cracking during cold rolling was reduced by the heat treatment, and also by cold rolling perpendicular to the fibers. Corresponding to edge cracking, lateral spread of the strip was greater in the case of cold rolling parallel to the fibers than in that perpendicular to the fibers. Heat treatments before cold rolling reduced the tensile strength of rolled sheets, while cold rolling enhanced the strength of cast strips. Although tensile strength of the as-cast strip largely depended on the direction of the fiber alignment, cold rolled strips showed less anisotropic tensile properties.

Strength and ductility in TiAl alloys

Abstract Tensile behavior of two-phase TiAl alloys at room temperature (RT) is analyzed for duplex and lamellar microstructural forms. The Hall-Petch relationship with high constants in fully-lamellar material is explained as a combined function of grain-size and deformation-anisotropy. The low ductility and its inverse relationship with grain size are explained using the anisotropic tensile properties of lamellar structures and assuming that the fracture is controlled by the crack nucleation process involving the pile-ups of dislocations under shear stress. The crack initiation toughness and associated strains near the crack tip are used to explain the inverse relationship between ductility and toughness.

Anisotropy in Tensile Properties of Mozzarella Cheese

ABSTRACTEffects of sampling direction (parallel or perpendicular to protein fiber orientation), cheese type (low‐moisture, part‐skim, LMPS and reduced fat, RF) and deformation rate (5 and 25 cm/min) on fracture properties of Mozzarella cheese were determined with tensile tests. The fracture toughness, stress, and strain in the parallel direction were, respectively, 2.8, 2.1 and 1.4 times greater than those in the perpendicular direction. This verified that the Mozzarella cheese had anisotropic tensile properties. A composite‐material approach was used to explain the direction‐dependent properties. The toughness, stress, and strain values for RF cheese were, respectively, 5.9, 5.4, and 1.3 times those of LMPS cheese. The tensile properties of Mozzarella were also affected by deformation rate.

Anisotropic tensile viscoelastic properties of vascular graft materials tested at low strain rates

Mechanical matching of vascular grafts and host vessels has been suggested to be important in determining graft patency rates. In this context, we have examined the anisotropic viscoelastic properties of natural vessels and some synthetic replacements using low strain rate tensile testing of circumferential and longitudinal strips. The canine iliac artery and iliac vein were compared with 6 mm diameter woven and knitted Dacron® grafts, expanded polytetrafluoroethylene (PTFE) grafts, and helically constructed prototype Polyurethane grafts at wrap angles of 45, 60 and 75°. A thick-walled pressure vessel analysis was used to approximate physiological stress levels, and SEM was used to correlate anisotropic properties with graft wall structure.