Showing papers on "Tensile testing published in 2012"

Microstructural and mechanical approaches of the selective laser melting process applied to a nickel-base superalloy

Abstract: This article aims at presenting the Nimonic 263 as-processed microstructure of the selective laser melting which is an innovative process. Because the melting pool is small and the scanning speed of the laser beam is relatively high, the as-processed microstructure is out-of-equilibrium and very typical to additive manufacturing processes. To match the industrial requirement, the microstructures are modified through heat treatments in order to either produce precipitation hardening or relieve the thermal stresses. Tensile tests at room temperature give rise to high mechanical properties close or above those presented by Wang et al. [1]. However, it is noted a strong anisotropy as a function of the building direction of the samples because of the columnar grain growth.

Tensile properties of an AlCrCuNiFeCo high-entropy alloy in as-cast and wrought conditions

Abstract: Extensive multistep forging at 950 °C was applied to the cast AlCuCrFeNiCo high-entropy alloy to transform the cast coarse dendritic structure into a fine equiaxed duplex structure consisting of the mixture of BCC and FCC phases, with the average grain/particle size of ∼1.5 ± 0.9 μm. Tensile properties of the alloy in the as-cast and forged conditions were determined in the temperature range of 20–1000 °C. The hot forged alloy was stronger and more ductile during testing at room temperature, than the as-cast alloy. The yield stress (YS), ultimate tensile strength (UTS), and tensile ductility ( δ ) of the forged condition were 1040 MPa, 1170 MPa, and 1%, respectively, against 790 MPa, 790 MPa and 0.2% for the as-cast condition. In both conditions, the alloy showed brittle to ductile transition (BDT), with a noticeable increase in the tensile ductility within a narrow temperature range. In the as-cast condition, this transition occurred between 700 and 800 °C, while in the forged condition, it was observed between 600 and 700 °C. With an increase in the testing temperature above the BDT, a continuous decrease in tensile flow stress and an increase in tensile ductility were observed. In the temperature range of 800–1000 °C, the forged alloy showed superplastic behavior. The tensile elongation was above 400% and reached 860% at 1000 °C.

Size effects on elasticity, yielding, and fracture of silver nanowires: In situ experiments

Abstract: This paper reports the quantitative measurement of a full spectrum of mechanical properties of fivefold twinned silver (Ag) nanowires (NWs), including Young's modulus, yield strength, and ultimate tensile strength. In-situ tensile testing of Ag NWs with diameters between 34 and 130 nm was carried out inside a scanning electron microscope (SEM). Young's modulus, yield strength, and ultimate tensile strength all increased as the NW diameter decreased. The maximum yield strength in our tests was found to be 2.64 GPa, which is about 50 times the bulk value and close to the theoretical value of Ag in the $\ensuremath{\langle}110\ensuremath{\rangle}$ orientation. The size effect in the yield strength is mainly due to the stiffening size effect in the Young's modulus. Yield strain scales reasonably well with the NW surface area, which reveals that yielding of Ag NWs is due to dislocation nucleation from surface sources. Pronounced strain hardening was observed for most NWs in our study. The strain hardening, which has not previously been reported for NWs, is mainly attributed to the presence of internal twin boundaries.

Effects of extrusion and heat treatment on the mechanical properties and biocorrosion behaviors of a Mg-Nd-Zn-Zr alloy.

Abstract: Mechanical properties at room temperature and biocorrosion behaviors in simulated body fluid (SBF) at 37 °C of a new type of patented Mg–3Nd–0.2Zn–0.4Zr (hereafter, denoted as JDBM) alloy prepared at different extrusion temperatures, as well as heat treatment, were studied. The mechanical properties of this magnesium alloy at room temperature were improved significantly after extrusion and heat treatment compared to an as-cast alloy. The results of mechanical properties show that the yield strength (YS) decreases with increasing extrusion temperature. The tensile elongation decreases a little while the ultimate tensile strength (UTS) has no obvious difference. The yield strength and ultimate tensile strength were improved clearly after heat treatment at 200 °C for 10 h compared with that at the extrusion state, which can be mainly contributed to the precipitation strengthening. The biocorrosion behaviors of the JDBM alloy were studied using immersion tests and electrochemical tests. The results reveal that the extruded JDBM alloy and the aging treatment on the extruded alloy show much better biocorrosion resistance than that at solid solution state (T4 treatment), and the JDBM exhibited favorable uniform corrosion mode in SBF.

Influence of drying on the mechanical behaviour of flax fibres and their unidirectional composites

Abstract: The microstructure of flax fibres can be considered as a laminate with layers reinforced by cellulose fibrils. During a single fibre tensile test the S2 layer is subjected to shear. At room temperature, natural fibres contain water absorbed in the cell-walls. This paper examines the influence of this water at two scales: on the tensile behaviour of the flax fibres and on unidirectional plies of flax reinforced epoxy. Drying (24 h at 105 °C) is shown to reduce both failure stress and failure strain significantly. Analysis of normal stresses at the accomodation threshold provides an estimation of the shear strength of secondary cell walls as 45 MPa for fibres containing 6.4% by weight of water and only 9 MPa for dried fibres. Results from tensile tests on unidirectional flax/epoxy composites, reinforced by as-received and dried fibres, confirm the influence of drying on strength properties.

Strength and ductility-related properties of ultrafine grained two-phase titanium alloy produced by warm multiaxial forging

Abstract: The most important room temperature mechanical properties of two-phase Ti–6Al–4V alloy with ultrafine grained microstructure were studied in the present work. Bulk preforms of the alloy with ultrafine grained microstructure were produced by warm multiaxial forging. The final structure consisted of alpha and beta particles with size of 150–500 nm depending on deformation temperature. The mechanical properties of ultrafine grained material were carried out in comparison with conventionally heat-strengthened condition of the alloy. Room-temperature strength of the ultrafine grained material was found to be 16–33% higher than that of the heat-strengthened alloy. However, ductility-related properties including tensile elongation, impact toughness, fatigue crack growth resistance and fracture toughness noticeably decreased with decreasing grain size. The efforts to increase ductility the ultrafine grained alloy by annealing was restricted by rather intensive softening of the material. Considerable enhancement of ductility of the alloy with a bi-modal microstructure consisting of large primary alpha in UFG alpha/beta matrix was shown.

Factors Affecting the Properties of Friction Stir Welds between Aluminum and Magnesium Alloys

Abstract: Extruded Al–0.5Mg–0.3Si (6063) aluminum and rolled Mg–3Al–1Zn (AZ31B) magnesium alloy sheets were joined by Friction Stir Welding. The dissimilar metal weld joints exhibit tortuous interfaces. The nugget grain size on both the Al and Mg sides monotonically increase as the tool rotational speed increases. The midplane microhardness traverses show fluctuating hardness peaks due to the presence of different microstructural phases in the nugget zone. The maximum tensile strength of the dissimilar weld joint is 68% of the 6063-T5 base metal with a maximum elongation of 1%. The low ductility is attributed to the formation of brittle intermetallic phases at the Al–Mg interface in the weld joint. Transverse tensile test results are correlated with several interface features: (1) actual interface length, (2) extent of interpenetration between the aluminum and magnesium base metals, (3) maximum intermetallic layer thickness, and (4) area fraction of micro-void coalescence on the tensile fracture surfaces. Results indicate that maximizing the extent of interpenetration and hence promoting mechanical interlocking between the metallic phases, is the key to attaining reasonable transverse strength in Al–Mg dissimilar metal welds. The welding process control variables that promote higher mechanical interlocking of the weld joints are discussed. The process response variables (welding torque, power, x-axis force and the nugget grain size) are presented for a range of welding parameters.

Novel Technique for Static and Dynamic Shear Testing of Ti6Al4V Sheet

Abstract: Few shear test techniques exist that cover the range of strain rates from static to dynamic. In this work, a novel specimen geometry is presented that can be used for the characterisation of the shear behaviour of sheet metals over a wide range of strain rates using traditional tensile test devices. The main objectives during the development of the shear specimen have been 1) obtaining a homogeneous stress state with low stress triaxiality in the zone of the specimen subjected to shear and 2) appropriateness for dynamic testing. Additionally, avoiding premature specimen failure due to edge effects was aimed at. Most dimensional and practical constraints arose from the dynamic test in which the specimen is loaded by mechanical waves in a split Hopkinson tensile bar device. Design of the specimen geometry is based on finite element simulations using ABAQUS/Explicit. The behaviour of the specimen is compared with the more commonly used simple shear specimen with clamped grips. Advantages of the new technique are shown. The technique is applied to Ti6Al4V sheet. During the high strain rate experiments high speed photography and digital image correlation are used to obtain the local shear strain in the specimen. Comparison of experimental and numerical results shows good correspondence.

Predicting the Uniaxial Compressive and Tensile Strengths of Gypsum Rock by Point Load Testing

Abstract: Uniaxial compressive and tensile strengths are considered key properties for characterising rock material in engineering practice. They are determined, directly and indirectly, as described by the International Society for Rock Mechanics (ISRM) (1985) and the American Society for Testing Materials (ASTM) (1986). The point load strength index (PLSI), an indirect strength test, has been correlated empirically with both the compressive and tensile strengths of rock. The point load test (PLT) may be applied to cylindrical specimens, either along the axis, or the diameter, but as noted by Chau (1998), the diametral PLT is preferred (Bieniawski 1975). In the PLT, rock specimens (of cylindrical, prismatic, or irregular form) are loaded between two platen contact points, and they fail by the development of one or more extensional planes containing the line of loading. According to recommendations by ISRM (1985) and the standards of ASTM (1986), these types of failure mode are regarded as valid, whereas deviations from them are treated as invalid. Although relatively simple, the uniaxial compressive test is time-consuming and expensive, and it requires wellprepared cores. For these reasons, indirect tests such as the PLT, the Schmidt hammer rebound test, and sound velocity measurements (Sonmez et al. 2004, 2006) are often used to predict the uniaxial compressive strength (UCS). Tensile strength may be measured directly, but in practice it is difficult to do so. Instead, the indirect method of Brazilian testing can be used, as recommended by ISRM (1978). The Brazilian test measures tensile strength indirectly by developing tension across the diameter of a rock disc that is subjected to compression through a vertical load. In practice, however, the test has limitations, and more experimental data are needed to substantiate the correlation between the point load index and the UCS. The objective of this paper is to compare all of the PLT methods and their usefulness in practical applications. This study presents the PLSI (Is(50)) (air-dried and saturated states) obtained by three methods (axial, diametral, and irregular), and establishes the relationships between them. We then develop empirical equations relating UCS and Brazilian tensile strength (BTS) to Is(50) with the aim of obtaining simple, fast, practical and economical estimates of the UCS and BTS of gypsum rocks.

Influence of environmental relative humidity on the tensile and rotational behaviour of hemp fibres

Abstract: The aim of this study is to throw new light on the influence of moisture on the mechanical properties of hemp fibres. Indeed, the behaviour of plant-based fibres strongly depends on their humidity. Although this topic has been relatively well treated for the case of wood, the literature on fibre stemming from annual plants is unfortunately poor. This purpose is, however, of great importance, particularly in view of the production of high-performance composites. The influence of environmental conditions on the static and dynamic tensile moduli and the strength of elementary fibres are investigated using a versatile experimental setup. Novel equipment was also designed to measure the rotation of a fibre about its axis when it was subjected to static loading and moisture variations. Water sorption is shown to have a significant influence on the apparent tensile stiffness, strength and fracture mode of such fibres, and is also shown to act like an activator of the stiffening phenomena under cyclic loading. A remarkable increase in the fibre stiffness of up to 250% is measured. Significant longitudinal elongation, reaching a value in excess of 2%, is associated with this increase in stiffness. The absorption and desorption of moisture also lead to substantial rotation of the fibre about its axis. Water sorption certainly involves a modification of the adhesion between cellulose microfibrils and the amorphous matrix. Under cyclic loading, the cellulose microfibrils could be able to creep into the relaxed amorphous matrix, leading to their re-arrangement, with more parallel orientations with respect to the fibre axis.

Dynamic Tensile Properties of Human Skin

Abstract: The mechanical properties of skin are important for a number of applications including surgery, dermatology, impact biomechanics and forensic science. Studies have shown that the anisotropic effects of skin have been linked to sample orientation with respect to contour lines of tension, i.e.the Langer’s lines. There have been numerous studies undertaken to calculate the influence of Langer’s lines on the mechanical properties of human skin at quasistatic strain rates; however, it is relatively unknown what occurs at dynamic speeds. This study conducts a number of dynamic mechanical tensile tests to investigate the influence dynamic speeds have on the mechanical properties of human skin. The testing protocol involves uniaxial tensile tests at three different dynamic speeds, 1m/s, 1.5m/s and 2m/s, performed using an Instron tensile test machine. A total of 33 tests were conducted on 3 human cadavers aged 85, 77 and 82. Samples were excised at specific locations and orientations with respect to the Langer’s lines. The purpose for this was to recognize the significance that location and orientation have on the mechanical properties of human skin. The mean ultimate tensile strength (UTS) was 27.2±9.3MPa, the mean strain energy was 4.9±1.5MJ/m3, the mean elastic modulus was 98.97±97MPa and the mean failure strain was 25.45±5.07%. This new material data for human skin can be applied to constitutive models in areas such as impact biomechanics, forensic science and computer‐assisted surgery.

Grain size and texture effects on deformation behavior of AZ31 magnesium alloy

Abstract: Cold rolled AZ31 magnesium alloy sheet was subjected to friction stir processing to generate four average grain sizes ranging from 0.8 to 9.6 μm. The processed material exhibited a strong basal fiber texture with the c -axis tilted about 35–55° towards the processing direction. The grain size and texture dependence of mechanical behavior were evaluated by using tensile testing along two orthogonal directions. Remarkably high ductility of ∼65% was achieved in relatively coarse grained material that fractured without developing necking when tested in the processing direction. The ductility decreased significantly to ∼10% for ultrafine grained material as the tensile yield strength increased from ∼53 MPa to ∼180 MPa. Grain size had limited influence on ductility of processed material tested in transverse direction, but reduced the uniform elongation to ∼2% for ultrafine grained material which exhibited ∼320 MPa yield strength. Accompanying the significant anisotropy in tensile strength in two directions, the deformation of processed AZ31 in the processing direction was mainly accommodated through basal slip and extension twinning (except for ultrafine grained material); however, the deformation of material in transverse direction was dominated by non-basal slip. Influences of grain size and texture on mechanical behavior were studied in terms of work-hardening and deformation mechanisms.

Evaluation of hydrogen trapping in high strength steels by thermal desorption spectroscopy

Abstract: High strength steels are materials of considerable interest and are increasingly used but appear to be more prone to hydrogen embrittlement (HE). In this work, four high strength steels and a pure iron, as a reference material, were studied by thermal desorption spectroscopy (TDS) in order to evaluate hydrogen trapping in these materials and to correlate it to the observed response of these materials to the previously evaluated effect of hydrogen on their mechanical properties. It was found that the materials which display a rather fast and significant ductility loss during hydrogen charged tensile testing contained a higher amount of diffusible hydrogen after charging. The activation energies for the peaks present in the TDS spectra were calculated for all materials and indicated that the activation energies for all low temperature peaks are pretty similar.

Effects of talc on the mechanical and thermal properties of polylactide

Abstract: Polylactide (PLA) composites with various talc content were prepared by melt extrusion. The thermal, dynamic mechanical, tensile and flexural properties, and fracture surface morphologies of neat PLA and PLA/talc composites were investigated and compared. The results showed that talc had significant nucleation effect and the cold crystallization temperature of PLA decreased with talc concentration. The thermal degradation and heat distortion temperature of PLA were slightly enhanced by compounding with talc. Talc showed significant reinforcing and toughening effects on PLA, the tensile strength, flexural strength and modulus increased with talc content ranging from 0 to 24.3 wt %. The results of tensile test showed that the elongation at break increased with talc content up to 18.1 wt % with obvious changes in fracture behavior, changing from brittle to ductile, when talc content increased to 24.3%, samples failed in a brittle manner with low elongation at break. The fracture surface morphologies showed that the talc layers were partially delaminated, aligned along the flow direction, and uniformly dispersed in the PLA matrix. The results obtained by SEM and FTIR confirmed that the interfacial adhesion between talc and PLA matrix was good. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012