Showing papers on "Tensile testing published in 2005"

Single lamellar mechanics of the human lumbar anulus fibrosus

Abstract: The mechanical behavior of the entire anulus fibrosus is determined essentially by the tensile properties of its lamellae, their fiber orientations, and the regional variation of these quantities. Corresponding data are rare in the literature. The paper deals with an in vitro study of single lamellar anulus lamellae and aims to determine (i) their tensile response and regional variation, and (ii) the orientation of lamellar collagen fibers and their regional variation. Fresh human body-disc-body units (L1–L2, n=11) from cadavers were cut midsagittally producing two hemidisc units. One hemidisc was used for the preparation of single lamellar anulus specimens for tensile testing, while the other one was used for the investigation of the lamellar fiber orientation. Single lamellar anulus specimens with adjacent bone fragments were isolated from four anatomical regions: superficial and deep lamellae (3.9±0.21 mm, mean ± SD, apart from the outer boundary surface of the anulus fibrosus) at ventro-lateral and dorsal positions. The specimens underwent cyclic uniaxial tensile tests at three different strain rates in 0.15 mol/l NaCl solution at 37°C, whereby the lamellar fiber direction was aligned with the load axis. For the characterization of the tensile behavior three moduli were calculated: Elow (0–0.1 MPa), Emedium (0.1–0.5 MPa) and Ehigh (0.5–1 MPa). Additionally, specimens were tested with the load axis transverse to the fiber direction. From the second hemidisc fiber angles with respect to the horizontal plane were determined photogrammetrically from images taken at six circumferential positions from ventral to dorsal and at three depth levels. Tensile moduli along the fiber direction were in the range of 28–78 MPa (regional mean values). Superficial lamellae have larger Emedium (p=0.017) and Ehigh (p=0.012) than internal lamellae, and the mean value of superficial lamellae is about three times higher than that of deep lamellae. Tensile moduli of ventro-lateral lamellae do not differ significantly from the tensile moduli of dorsal lamellae, and Elow is generally indifferent with respect to the anatomical region. Tensile moduli transverse to the fiber direction were about two orders of magnitude smaller (0.22±0.2 MPa, mean ± SD, n=5). Tensile properties are not correlated significantly with donor age. Only small viscoelastic effects were observed. The regional variation of lamellar fiber angle ϕ is described appropriately by a regression line |ϕ|=23.2+0.130×α (r2=0.55, p<0.001), where α is the polar angle associated with the circumferential position. The single anulus lamella may be seen as the elementary structural unit of the anulus fibrosus, and exhibits marked anisotropy and distinct regional variation of tensile properties and fiber angles. These features must be considered for appropriate physical and numerical modeling of the anulus fibrosus.

Ultrahigh strength and high ductility of bulk nanocrystalline copper

Abstract: We have synthesized artifact-free bulk nanocrystalline copper samples with a narrow grain size distribution (mean grain size of 23nm) that exhibited tensile yield strength about 11 times higher than that of conventional coarse-grained copper, while retaining a 14% uniform tensile elongation. In situ dynamic straining transmission electron microscope observations of the nanocrystalline copper are also reported, which showed individual dislocation motion and dislocation pile-ups. This suggests a dislocation-controlled deformation mechanism that allows for the high strain hardening observed. Trapped dislocations are observed in the individual nanograins.

Microstructure and mechanical behavior of porous sintered steels

Abstract: The microstructure and mechanical properties of sintered Fe–0.85Mo–Ni steels were investigated as a function of sintered density. A quantitative analysis of microstructure was correlated with tensile and fatigue behavior to understand the influence of pore size, shape, and distribution on mechanical behavior. Tensile strength, Young's modulus, strain-to-failure, and fatigue strength all increased with a decrease in porosity. The decrease in Young's modulus with increasing porosity was predicted by analytical modeling. Two-dimensional microstructure-based finite element modeling showed that the enhanced tensile and fatigue behavior of the denser steels could be attributed to smaller, more homogeneous, and more spherical porosity which resulted in more homogeneous deformation and decreased strain localization in the material. The implications of pore size, morphology, and distribution on the mechanical behavior and fracture of P/M steels are discussed.

Structure and properties of electrospun PLLA single nanofibres.

Abstract: An electrospinning method was used to spin semi-crystalline poly(L-lactide) (PLLA) nanofibres. Processing parameter effects on the internal molecular structure of electrospun PLLA fibres were investigated by x-ray diffraction (XRD) and differential scanning calorimetry (DSC). Take-up velocity was found as a dominant parameter to induce a highly ordered molecular structure in the electrospun PLLA fibres compared to solution conductivity and polymer concentration, although these two parameters played an important role in controlling the fibre diameter. A collecting method of a single nanofibre by an electrospinning process was developed for the tensile tests to investigate structure-property relationships of the polymer nanofibres. The tensile test results indicated that higher take-up velocity caused higher tensile modulus and strength due to the ordered structure developed through the process.

The effect of Ca and rare earth elements on the microstructure, mechanical properties and corrosion behavior of AZ91D

Abstract: The microstructure, mechanical properties and corrosion behavior of AZ91 with addition of Ca and rare earth elements (REs) were investigated using tensile tests, X-ray diffraction, SEM, EDX, immersion tests and electrochemical polarization experiments. The addition of 1%Ca led to the formation of reticular Al 2 Ca phase, which improved the corrosion resistance of AZ91D alloys. The reticular Al 2 Ca phase had a detrimental influence on the mechanical properties of AZ91 alloys; however, the addition of REs improved the ultimate tensile strength of the AZ91 alloy, but the corrosion resistance increased slightly compared with the addition of Ca. With the addition of 1%Ca and 1%REs to AZ91, the ultimate tensile strength increased by 15.9% and the corrosion rate decreased to 0.086 mg cm −2 day −1 due to the formation of the reticular Al 2 Ca phase, which acted as an effective barrier against corrosion.

Disk-shaped Compact Tension Test for Asphalt Concrete Fracture

Abstract: A disk-shaped compact tension (DC(T)) test has been developed as a practical method for obtaining the fracture energy of asphalt concrete. The main purpose of the development of this specimen geometry is the ability to test cylindrical cores obtained from in-place asphalt concrete pavements or gyratory-compacted specimens fabricated during the mixture design process. A suitable specimen geometry was developed using the ASTM E399 standard for compact tension testing of metals as a starting point. After finalizing the specimen geometry, a typical asphalt concrete surface mixture was tested at various temperatures and loading rates to evaluate the proposed DC(T) configuration. The variability of the fracture energy obtained from the DC(T) geometry was found to be comparable with the variability associated with other fracture tests for asphalt concrete. The ability of the test to detect changes in the fracture energy with the various testing conditions (temperature and loading rate) was the benchmark for determining the potential of using the DC(T) geometry. The test has the capability to capture the transition of asphalt concrete from a brittle material at low temperatures to a more ductile material at higher temperatures. Because testing was conducted on ungrooved specimens, special care was taken to quantify deviations of the crack path from the pure mode I crack path. An analysis of variance of test data revealed that the prototype DC(T) can detect statistical differences in fracture energy resulting for tests conducted across a useful range of test temperatures and loading rates. This specific analysis also indicated that fracture energy is not correlated to crack deviation angle. This paper also provides an overview of ongoing work integrating experimental results and observations with numerical analysis by means of a cohesive zone model tailored for asphalt concrete fracture behavior.

Behavior of hybrid-fiber engineered cementitious composites subjected to dynamic tensile loading and projectile impact

Abstract: The characteristics of engineered cementitious composites (ECCs) subjected to dynamic tensile loading and high-velocity projectile impact have been investigated and are reported in this paper. Hybrid-fiber ECC containing a combination of high-modulus steel fibers and relatively low modulus polyethylene fibers was adopted to achieve a desired balance between the ultimate strength and the strain capacity of the material required for impact- and blast-resistant structures. Dynamic uniaxial tensile tests at varying strain rates of 2× 10−6 to 0.2 s−1 were carried out, and ECC was found to be able to provide much higher enhancement in tensile strength than plain concrete and still be able to maintain pronounced tensile strain-hardening behavior. At higher rates of strain, ECC showed multiple-cracking behavior, similar to that observed from quasi-static tests, with tight crack width of about 0.1 mm . The results from high-velocity (300–750 m∕s) impact tests demonstrated the potential of ECC in providing improved...

Evaluation of mechanical properties using shear–punch testing

Abstract: The evaluation of mechanical properties like yield and ultimate tensile strengths from shear–punch tests is important when the availability of material is limited. A shear–punch test setup was built in our laboratory and the mechanical properties for different materials; mild steel, pure Al, Zn, brass (Cu–30% Zn by wt.), Al 6061, Austenitic and Martensitic stainless steels were evaluated. A new method using 1% offset criterion in conjunction with normalized shear–punch curves was used to measure the shear yield strength. A linear correlation between the shear data and tensile data was established for yield and ultimate strengths. The variation of the yield and ultimate shear strength was studied as a function of the sample thickness and die–punch clearance for soft, medium and high strength materials.

Deformation Behavior of Bimodal Nanostructured 5083 Al Alloys

Abstract: Cryomilled 5083 Al alloys blended with volume fractions of 15, 30, and 50 pct unmilled 5083 Al were produced by consolidation of a mixture of cryomilled 5083 Al and unmilled 5083 Al powders. A bimodal grain size was achieved in the as-extruded alloys in which nanostructured regions had a grain size of 200 nm and coarse-grained regions had a grain size of 1 µm. Compression loading in the longitudinal direction resulted in elastic-perfectly plastic deformation behavior. An enhanced tensile elongation associated with the occurrence of a Luders band was observed in the bimodal alloys. As the volume fraction of coarse grains was increased, tensile ductility increased and strength decreased. Enhanced tensile ductility was attributed to the occurrence of crack bridging as well as delamination between nanostructured and coarse-grained regions during plastic deformation.

Linear friction welding of Ti-6Al-4V: Processing, microstructure, and mechanical-property inter-relationships

Abstract: The linear friction welding behavior of Ti-6Al-4V was investigated using varying processing conditions of frequency (15 to 70 Hz), amplitude (1 to 3 mm), pressure (50 to 90 MPa), and axial shortening (1 to 2 mm). Examination of linear friction welded Ti-6Al-4V using microscopic techniques indicated that the process requires certain critical conditions at the interface and its adjacent region to be reached for producing joints without structural defects along the weld centerline, such as voids or oxide inclusions. Characterization of the weldments included analysis of the microstructural features of the weld and thermomechanically affected zones (TMAZs) in relation to the parent material. It was observed that in the weld region, exposure to supertransus temperatures (>995 °C) combined with hot-deformation working and rapid cooling after joining produced recrystallization of the beta grain structure that had a Widmanstatten alpha-beta transformation microstructure. In the TMAZ, the bimodal microstructure of the parent material was deformed and the presence of elongated alpha grains with broken beta-phase particles was established. Through examination of the mechanical properties, using microhardness and tensile testing, the integrity of the joints was determined in order to assess the impact of the various processing parameters and to define the optimum welding conditions.

Tensile strength and ductility of ultra-fine-grained nickel processed by severe plastic deformation

Abstract: The structure and mechanical properties of Ni subjected to severe plastic deformation by means of equal channel angular pressing (ECAP) followed by cold rolling or high-pressure torsion were investigated. A material with uniform ultra-fine-grained (UFG) microstructure and mean grain size in the range from 100 to 600 nm, depending on the processing procedure, was obtained. Tensile tests at room temperature revealed ultimate tensile strength values in the range from 840 to 1270 MPa and an elongation to fracture in the range from 7 to 12% depending on the processing method. Annealing at 200 °C of the sample deformed by ECAP and cold rolling led to the best combination of strength and plasticity. The strength of the material was well above the level expected from the Hall–Petch rule. We explained this high strength by taking into account dislocations trapped at grain boundaries (TLDs). In ultra-fine-grained (UFG) materials the specific surface of grain boundaries is high and therefore the TLDs density is high as well. The fracture and deformation relief indicate an important role of grain-boundary sliding and grain rotation as deformation mechanisms. The UFG high-strength Ni with relatively good ductility has a potential for applications in particular in microsystems, where the cross section of the material is in the micrometer range but still must cross a sufficient number of grains to look structurally uniform.

Warm deformation behavior of hot-rolled AZ31 Mg alloy

Abstract: Uniaxial tensile test was employed to evaluate the warm deformation properties of hot-rolled AZ31 Mg alloy at a temperature range of 50–200°C and a strain rate range of 1.4 × 10−3 s−1–1.4 × 10−1 s−1. The dynamic recrystallization (DRX) and twinning during the warm deformation were observed by optical microscopy (OM) and transmission electronic microscopy (TEM). It is shown that twinning characterized by a compound mode with differently oriented twins intersecting each other is the dominant deformation mechanism at low temperatures and initial deformation stage. The distortion energy accumulated by twinning is the reason for the occurrence of DRX.

Auxetic compliant flexible PU foams: static and dynamic properties

Abstract: The paper describes the manufacturing and tensile testing of auxetic (negative Poisson's ratio) thermoplastic polyurethane foams, both under constant strain rate and sinusoidal excitation. The foams are produced from conventional flexible polyurethane basis following a manufacturing route developed in previous works. The Poisson's ratio behaviour over tensile strain has been analyzed using an Image Data processing technique based on Edge Detection from digital images recorded during quasi-static tensile test. The samples have been subjected to tensile and compressive tests at quasi-static and constant strain-rate values (up to 12 s -1 ). Analogous tests have been performed over iso-volumetric foams samples, i.e., foams subjected to the same volumetric compression of the auxetic ones, exhibiting a near zero Poisson's ratio behaviour. The auxetic and non-auxetic foams have been also tested under sinusoidal cycling load up to 10 Hz, with maximum pre-strain applied of 12%. The hysteresis of the cycling loading curve has been measured to determine the damping hysteretic loss factor for the various foams. The measurements indicate that auxetic foams have increased damping loss factor of 20% compared to the conventional foams. The energy dissipation is particularly relevant in the tensile segment of the curve, with effects given by the pre-strain level imposed on the samples.

On the Measurement of the Tensile Strength of Soft Rocks

Abstract: This paper reports on a comparative study of various types of experimental tests for measuring the tensile strength of rocks and rock-like materials. A critical assessment is presented of some widely used laboratory techniques on the basis of experimental data from the literature and from the laboratory investigation performed in this study. Tests were carried out using a triaxial apparatus recently set up at Milan University of Technology. This was designed to reduce random misalignments between specimen and loading frame, which are typical of conventional triaxial cells with external tie bars. The apparatus was then modified to perform various types of tests for determining the tensile strength of materials. An artificial building stone and a natural calcarenite of the Gravina di Puglia geological formation, sampled at Montescaglioso (Matera-Italy) were tested in this research. The experimental investigation included various types of tests, namely the uni-axial, the Brazilian, the ring, the three and four points bending and the Luong test. Specimens of both materials were also compressed to failure in unconfined conditions and loaded cyclically in unconfined tension and compression, Young’s moduli being measured by means of local instrumentation.

A microelectromechanical load sensor for in situ electron and x-ray microscopy tensile testing of nanostructures

Abstract: We report on the performance of a microelectromechanical system (MEMS) designed for the in situ electron and x-ray microscopy tensile testing of nanostructures, e.g., carbon nanotubes and nanowires. The device consists of an actuator and a load sensor with a gap in between, across which nanostructures can be placed, nanowelded, and mechanically tested. The load sensor is based on differential capacitance measurements, from which its displacement history is recorded. By determining the sensor stiffness, the load history during the testing is obtained. We calibrated the device and examined its resolution in the context of various applications of interest. The device is the first true MEMS in which the load is electronically measured. It is designed to be placed in scanning and transmission electron microscopes and on x-ray synchrotron stages.

Active metal brazing and characterization of brazed joints in titanium to carbon–carbon composites

Abstract: The Ti-metal/C-C composite joints were formed by reactive brazing with three commercial brazes, namely, Cu-ABA, TiCuNi, and TiCuSiI. The joint microstructures were examined using optical microscopy and scanning electron microscopy (SEM) coupled with energy dispersive spectrometry (EDS). The results of the microstructure analysis indicate solute redistribution across the joint and possible metallurgical bond formation via interdiffusion, which led to good wetting and spreading. A tube-on-plate tensile test was used to evaluate joint strength of Ti-tube/ C-C composite joints. The load-carrying ability was greatest for the Cu-ABA braze joint structures. This system appeared to have the best braze spreading which resulted in a larger braze/C-C composite bonded area compared to the other two braze materials. Also, joint loadcarrying ability was found to be higher for joint structures where the fiber tows in the outer ply of the C-C composite were aligned perpendicular to the tube axis when compared to the case where fiber tows were aligned parallel to the tube axis.

A study on stress corrosion cracking and hydrogen embrittlement of AZ31 magnesium alloy

Abstract: The stress corrosion cracking (SCC) behavior and pre-exposure embrittlement of AZ31 magnesium alloy have been studied by slow strain rate tensile (SSRT) tests in this paper. It is showed that AZ31 sheet material is susceptible to SCC in distilled water, ASTM D1.387 solution, 0.01 M NaCl and 0.1 M NaCl solution. The AZ31 magnesium alloy also becomes embrittled if pre-exposed to 0.01 M NaCl solution prior to tensile testing. The degree of embrittlement increased with increasing the pre-exposure time, It is proposed that both the pre-exposure embrittlement and SCC were due to hydrogen which reduces the cohesive strength. i,e,. hydrogen embrittlement, (c) 2005 Elsevier B.V. All rights reserved.