Rectangular Tensile Specimens Research Articles

DIC-based approach to predict post necking behavior for AA6061, AA7075 and their friction stir welded joints

In a tensile test, the precise measurement of the area at the necking section is crucial for predicting the post-necking true stress-strain behavior. In the conventional theoretical method, this area is linked to the engineering strain using the incompressibility criteria, which is not applicable in the post necking domain. The present work proposes a digital image correlation (DIC)-based technique with two cameras for estimating real-time area reduction at a necking section of a rectangular tensile specimen during a uniaxial tensile test. In the current study, the area at a given section is computed by measuring strain synchronously in the width and thickness planes of a tensile specimen and translating the change in lengths in both planes into a global coordinate system. The area computation of the proposed approach is successfully validated by measuring the necking area of a terminated tensile specimen (stopped before fracture) by optical microscope to an error in the range of 0.12–1.10%. Following verification, the post necking behaviors of aluminum alloys such as AA6061-T6 and AA7075-T6 are assessed. The current approach is further implemented to evaluate the area reduction and post necking behavior of similar and dissimilar friction stir welding (FSW) joints of AA6061-T6 and AA7075-T6 that possess process induced microstructural inhomogeneity. The current experimental approach effectively assessed the area reduction of a similar and dissimilar FSW joint influenced by weld inhomogeneity, which is otherwise complicated to contemplate using an analytical approach.

재료의 취성과 연성이 균열의 진전에 미치는 영향

In this paper, the effect of material properties on fracture behavior was studied using cohesive zone model and extended finite element method. The rectangular tensile specimen with a central inclined initial crack was modeled by plane stress elements. In the CZM modeling, cohesive elements were inserted between every bulk elements in the predicted crack propagation region before analysis, while in the XFEM the enrichment to the elements was added as needed during analysis. The crack propagation behavior was examined for brittle and ductile materials. For thin specimen configuration, wrinkle deformation was accounted for by geometrically nonlinear post-buckling analysis and the effect of wrinkling on the crack propagation was investigated.

Quantifying necking of rectangular tensile specimens using a mirror-based image analysis system

The cross-sectional area of a neck in a rectangular tensile specimen is not easily measured. In this paper, a technique for accurately quantifying instantaneous necking geometry of rectangular specimens, using a novel mirror setup and high speed camera, is discussed. The technique is non-contact and allows for the sides and front of the specimen to be imaged on one plane with one camera. For this study, a rectangular Sn tensile specimen was tested at 10s−1. DIC results and stress–strain behavior measured using the mirror fixture are briefly discussed.

Finite Element Analysis of Tensile Behavior of Ductile Steel with Defects

The 34CrMo4 material as an excellent alloy has been increasingly applied to the design and manufacture of pressure vessel and piping. However, the potential geometrical defects affect their mechanical performance to some extent. In this article, a parametric finite element analysis using ANSYS-APDL (Ansys Parametric Design Langrage) is performed to predict the tensile behavior of the 34CrMo4 steel rectangular tensile specimens with defects using the Gurson–Tvergaar–Needleman model which was originally developed to describe the ductile fracture initiation of metals. The defects are simulated using the node deflection technique and the influence of various defect sizes and material parameters on the tensile results is investigated. By comparison, the predicted tensile results using finite element analysis are in good agreement with those by experiments in terms of the elongation and tensile strengths. Besides, results show both the elongation and the tensile strength decrease with increasing defect sizes, but the defects affect the elongation more remarkably than the tensile strength.

Evaluation of fatigue life and crack growth rates in 7050-T7451 aluminum plate for T-L and L-S oriented failure under truncated spectra loading

Spectrum crack growth testing of 7050-T7451 plate was performed for T-L and L-S specimen orientations to determine the influence of spectrum truncation on fatigue crack growth rates and overall life. This testing was performed on center-hole (double crack), flat, rectangular tensile specimens machined from material blanks cut from 10.16 cm plate. Additional comparison T-L tests were also accomplished using blanks from available 7050-T7451 1.27 cm plate. Behavior of through-thickness long (>5 mm) cracks is examined. Spectrum loading used for the testing was based on a nominal fighter load spectra and truncation levels of testing were comprised of baseline (5%), plus 20% and 30% ranges. The target, ordered tensile-compressive, stress levels were based on a combination of legacy and predicted use of US fighter aircraft. Results produced representative trends in life-to-failure increases for truncation levels relative to 5% truncated levels for the L-S and T-L orientation specimens. Crack growth rate data was recorded and comparisons are exhibited for varied orientation and crack length. Findings show that although relatively small changes in life are experienced due to orientation, L-S oriented plate material life is affected by the greatest extension of up to 17%. Crack growth rates for shorter cracks in the L-S material exceed growth rates in the T-L oriented material by more than two times the rate. Characteristics of splitting, crack wandering, branching, and shielding were observed in the L-S specimen tests. These potentially undesirable characteristics resulted in temporary crack arrest or retardation in the direction perpendicular to loading and resulted in overall specimen rupture well beyond the life predicted critical crack lengths.

Nanostructure Evolution during Uni-Axial Deformation of PET – A WAXS and SAXS Study Using Synchrotron Radiation

In this work, the structural evolution and damage of PET during stretching is assessed by wide- and small-angle X-ray scattering (respectively, WAXS and SAXS) experiments in specimens pre-deformed at different strain levels (ex-situ characterization). Injection moulded PET rectangular tensile specimens were stretched (at 2 mm/min) into the plastic domain in a universal test machine at different strain levels at room temperature. The structure of the central zone of the deformed specimens was then characterized by WAXS and SAXS experiments using an X-ray synchrotron source. PET was initially (before stretching) amorphous. A strong molecular orientation in the stretching direction is quickly developed for the initial plastic deformation levels, evidenced by strong equatorial WAXS reflections. This orientation rapidly levels off, remaining constant during further stretching. The WAXS patterns are accompanied with no reflections on SAXS, evidencing a local ordering phenomenon, typical of nematic liquid-crystalline structures. The SAXS patterns evidence the occurrence of some voiding in the cold drawing regime just after yielding. These anisotropic voids are oriented perpendicular to the stretching direction, as in a craze-like structure. The void size drastically increases at the onset of the strong strain hardening behaviour.

Mechanical damage to the intervertebral disc annulus fibrosus subjected to tensile loading

Damage of the annulus fibrosus is implicated in common spinal pathologies. The objective of this study was to obtain a quantitative relationship between both the number of cycles and the magnitude of tensile strain resulting in damage to the annulus fibrosus. Four rectangular tensile specimens oriented in the circumferential direction were harvested from the outer annulus of 8 bovine caudal discs ( n=32) and subjected to one of four tensile testing protocols: (i) ultimate tensile strain (UTS) test; (ii) baseline cyclic test with 4 series of 400 cycles of baseline cyclic loading (peak strain=20% UTS); (iii & iv) acute and fatigue damage cyclic tests consisting of 4×400 cycles of baseline cyclic loading with intermittent loading to 1 and 100 cycles, respectively, with peak tensile strain of 40%, 60%, and 80% UTS. Normalized peak stress for all mechanically loaded specimens was reduced from 0.89 to 0.11 of the baseline control levels, and depended on the magnitude of damaging strain and number of cycles at that damaging strain. Baseline, acute, and fatigue protocols resulted in permanent deformation of 3.5%, 6.7% and 9.6% elongation, respectively. Damage to the laminate structure of the annulus in the absence of biochemical activity in this study was assessed using histology, transmission electron microscopy, and biochemical measurements and was most likely a result of separation of annulus layers (i.e., delamination). Permanent elongation and stress reduction in the annulus may manifest in the motion segment as sub-catastrophic damage including increased neutral zone, disc bulging, and loss of nucleus pulposus pressure. The preparation of rectangular tensile strip specimens required cutting of collagen fibers and may influence absolute values of results, however, it is not expected to affect the comparisons between loading groups or dose-response reported.

MIM industry finds firm foothold in Japan

A 24 factorial design was conducted to establish the effects of powder injection molding (PIM) parameters on the shrinkage properties of the widely used FeNi powder system. Four process parameters were analyzed simultaneously: (i) the debinding method, i.e., solvent condensation versus vacuum; (ii) the sintering heating rate; (iii) the sintering hold temperature; and (iv) the sintering hold time. Dimensional measurements of the length, width and thickness of green and sintered rectangular tensile specimens were made. An analysis of variance, together with the F-test, were used to determine the statistical significance of each of the parameters on the length, width and thickness shrinkages.

Determining true stress–strain curve for isotropic and anisotropic materials with rectangular tensile bars: method and verifications

Based on an extensive numerical study, the authors have recently developed a method for determining the true stress–strain curve for isotropic materials by using rectangular tensile specimens. In this method only load versus thickness reduction (at the diffuse necking zone) curve is needed. This method has been further developed for anisotropic materials. For anisotropic materials, both thickness and width reduction at the diffuse necking zone should be measured. In this paper, the effect of plastic anisotropy on the deformed cross-section profile has been further studied, and the proposed method has been experimentally verified against steel which was assumed to be isotropic (width to thickness strain ratio, r y ≈1) and aluminium alloys which were anisotropic with r y varied in the range 0.28< r y <0.66. It has been shown that the numerically predicted deformed cross-section shape is very close to the experimental one, measured from sectioned interrupted specimens. The true stress–strain curves determined from the rectangular tensile specimens were compared with the one determined from the conventional round tensile specimens, and very good agreement has been obtained. It has been found that the method using rectangular tensile specimens gives very consistent true stress–strain curves with small scatter.

Strain distributions made visible with image-shearing speckle pattern interferometry

The measurement of in-plane strain with image-shearing speckle pattern interferometry has so far been impeded by the lack of an efficient method for suppressing the out-of-plane displacement derivative. This paper presents a simple optical set-up with three light sources arranged in a particular symmetry and an associated procedure which allows accurate isolation of all six displacement derivatives which can contribute to the formation of fringes in image-shearing speckle pattern interferometry. The method uses a phase-shifting technique and is demonstrated on the deformation of a rectangular tensile specimen with a central hole. The measured in-plane strain components are compared with the results of finite element analysis. High quality fringe patterns are obtained which reveal even localized strain concentrations. The optical set-up proposed in this paper is well suited for applications in an industrial environment, and the associated procedure for isolating the displacement derivatives can easily be automated.

Tensile and tear properties of dental dam

The tensile and tear properties of highly extensible latex are sensitive to specimen shape. Three specimen shapes (ASTM D412 Die C dumbbell tensile specimen, rectangular tensile specimen with 1.74 mm hole, and ASTM D624 Die C tear specimen) were evaluated for proposed ANSI/ADA specification #90 for dental dams. Fresh and aged dental dams from two manufacturers (Aseptico and Hygenic) in three weights (thin, medium, and heavy) and from two other manufacturers (Ivory and Ivoclar) in one weight (medium) were tested. Means and standard deviations of 10 specimens for tensile strength (MPa), elongation (%), and tear strength (kN/m) are included herein. Data were analyzed by analysis of variance. Means were compared by a Tukey-Kramer interval calculated at the 0.05 significance level. The use of the dumbbell and tear specimens for the evaluation of dental dam should be reconsidered. The rectangular specimen with a hole is recommended for use in the proposed specification because of its sensitivity to condition (fresh versus aged) and manufacturer.

Statistical analysis of shrinkage variation for powder injection molding

A 2 4 factorial design was conducted to establish the effects of powder injection molding (PIM) parameters on the shrinkage properties of the widely used FeNi powder system. Four process parameters were analyzed simultaneously: (i) the debinding method, i.e., solvent condensation versus vacuum; (ii) the sintering heating rate; (iii) the sintering hold temperature; and (iv) the sintering hold time. Dimensional measurements of the length, width and thickness of green and sintered rectangular tensile specimens were made. An analysis of variance, together with the F-test, were used to determine the statistical significance of each of the parameters on the length, width and thickness shrinkages.

Comparison between Full Scale Tests and Small Scale Tests in Evaluating the Cracking Susceptibility of Line Pipe in Sour Environment.

Line pipes have possibility to encounter three types of crack morphology: SSC, HIBC/SWC, SOHIC (Stress Oriented HIC) in the sour environment. For modern line pipes, SOHIC is concerned under applied stress, particularly in softened heat-affected zone. In this study, an X65 UOE line pipe was evaluated as a CAPCIS type full ring test and a full pipe test were compared with tensile tests conforming to NACE standard TM0177-90 method A on the susceptibility to SOHIC in weld. A rectangular tensile specimen 6.4 mm in thickness provided the same result as the round bar specimen specified in the NACE standard in terms of threshold stress. Ruptured specimens showed SOHIC preferably induced in the softened HAZ. In contrast, no defect indication was obtained after the completion of the full ring test performed at the applied stress of 90% SMYS above the threshold stress. With regard to the full pipe test, no defect was observed when loaded with 90% SMYS with an exception of bead toe cracking caused by rather high applied stress due to stress concentration. The rectangular tensile test in which a single wide side was exposed to the environment was also conducted. No internal SOHIC was observed at the applied stress of 100% SMYS. And the single side exposure test with weld reinforcement exposed to the sour environment also reproduced the bead toe cracking. This study concludes that the NACE standard is more severe than CAPCIS type full ring test which can be substituted with the one-side exposed rectangular specimen and more severe than the full pipe test from the viewpoint of evaluating the susceptibility to SOHIC. This study proposes the single side exposure rectangular test as a realistic substitute for full scale tests.

Elastic-plastic fem calculations of the stress distribution of notches with different geometry

A two-dimensional elasto-plastic finite element analysis of double notched rectangular tensile specimens with different notch geometries has been performed. The maximum value of stress concentration below the notch is given as function of the applied stress for varying notch radius and notch angles. The results of the finite element method are compared with the predictions of the slip line theory.