The V-Notched Rail Shear Test

Experimental determination of deformation homogeneity and shear states using the digital image correlation method

Mechanical characterization in shear of human femoral cancellous bone: torsion and shear tests

Strain rate effect on in-plane shear strength of unidirectional polymeric composites

The interlaminar shear strength of composite materials is often determined by the short-beam shear test method. This type of test is satisfactory only so long as a pure shear failure occurs. Nonshear or mixed-mode failures, hence invalid data, can result if the interlaminar shear strength is too high with respect to the ultimate flexure strength, or if span-to-depth ratio or width-to-depth ratio is improperly chosen. Since the flexural stress is dependent on span length, various span-to-depth ratios of interest were investigated using beam theory to determine the interaction of shear and flexure stresses present in the short-beam specimen. These interactions are shown as a function of the direct stress in the short beam. Examination of the shear-flexure interaction was made by employing a failure criterion based on distortion energy. Failure was found limited to either shear mode at the center of the beam or flexural mode at the outer fiber. The combination of shear and flexure at intermediate locations is not of sufficient magnitude to cause failure. Since the probability of nonshear failure increases as interlaminar shear strength is improved without accompanying increases in flexural strength a means of choosing proper length-to-depth ratios knowing the approximate flexural-to-shear strength ratio is presented. The possibility of a flexural failure is minimized by incorporating a flexural stress to flexural strength ratio which will not be exceeded at the chosen length-to-depth ratio. The effect of the width-to-depth ratio on the shear stresses in the specimen is developed by a theory of elasticity solution. The formula currently being used to calculate the shear stresses is based on beam theory and assumes that the shear stresses are constant along the width of the specimen. The exact solution for an ortho-tropic beam shows a significant effect of the width-to-depth ratio on the magnitude and distribution of shear stresses in the short beam. The inter-laminar shear stress is highest at the edges of the specimen and lowest at the middle. Calibration curves for graphite-polymer, boron-polymer, and boron-aluminum have been developed to correct the shear stresses as given by the conventional beam theory formula for various values of width-to-depth ratios. Experimental data has been obtained on a graphite-polymer system for fiber orientations of both zero and ±45 deg. Conventional beam theory calculations show the interlaminar shear strength of the ±45-deg cross ply to be reduced significantly over that of the unidirectional specimens. Application of the theory of elasticity correction factors to these data indicate that the actual interlaminar shear strength for both orientations are approximately equal.

Determination of the in-plane shear modulus of unidirectional carbon fiber-reinforced plastics using digital image correlation and finite-element analysis

Typically, the reduction of the load and strain data obtained during an Iosipescu shear test assumes constant shear strain and shear stress distributions. While this is nominally correct and simplifies the data reduction, it provides no insight into the shear stress-shear strain distribution and can lead to theoretically inconsistent experimental results. In this study, an Idaho Iosipescu test fixture, two sizes of strain gages, an assumed power law for the strain distribution, and the Richard-Blacklock stress-strain relationship have been combined to model both the shear strain and the shear stress profile across the gage section. The results show a strain distribution dependent on both load and laminate layup and the difference between the shear stress and the shear strain profile. The initial shear moduli found from the nonlinear model show an insignificant difference between the two layups which is in agreement with composite theory.

Thickness-tapered cruciform specimens have previously been used to measure the biaxial strength of various carbon/epoxy cross-ply laminates. In the present work an alternative specimen production method was investigated that requires no machining of the gage section. A total of 27 specimens were tested to produce a complete failure envelope in the σ1-σ2 stress space. Results were compared with five specimens produced by the previous manufacturing method. In addition, finite element analysis (FEA) was conducted on both these specimens and resulting strains were to within 5% of the measured experimental results. Additional geometries were machined into the specimens in the continued effort to improve the specimen geometry to promote failure within the gage section for all stress ratios. Three separate modifications were made and seven specimens of each were tested at various stress ratios. Comparisons are made between experimental and FEA results.

Shear testing is one of the most complex testing areas where available methods and specimen geometries are different from each other. Therefore, a modified shear test specimen (MSTS) combining the simple uniaxial test with a zone of interest (ZOI) is tested which gives almost the pure shear. In this study, material parameters of polypropylene (PP) and high density polyethylene (HDPE) are first measured by tensile tests with a dogbone shaped specimen. These parameters are then used as an input for the finite element analysis. Secondly, a specially designed specimen (MSTS) is used to perform the shear stress tests in a tensile testing machine to get the results in terms of forces and extension, crack initiation etc. Scanning Electron Microscopy (SEM) is also performed on the shear fracture surface to find material behavior. These experiments are then simulated by finite element method and compared with the experimental results in order to confirm the simulation model. Shear stress state is inspected to find the usability of the proposed shear specimen. Finally, a geometry correction factor can be established for these two materials in this specific loading and geometry with notch using Linear Elastic Fracture Mechanics (LEFM). By these results, strain energy of shear failure and stress intensity factor (SIF) of shear of these two polymers are discussed in the special application of the screw cap opening of the medical or food packages with a temper evidence safety solution.

Mechanical properties of carbon‐epoxy composites are highly affected by the operating temperature. In this study, the effect of temperature on the compressive strength and in‐plane shear strength of composites has been analyzed. The unidirectional composites are processed by filament winding using T700 carbon fiber rovings and two different epoxy resin systems. The compressive strength measured from combined loading compression tests showed a decreasing trend with an increase in temperature. The compressive strength decreased from 700 to 400 MPa when the temperature increased from –20 to 150°C, which represents 54% reduction in strength. The in‐plane shear tests were performed using longitudinal and transverse extensometers and found that shear strength decreased by nearly 50%. Fractography of compression samples revealed that the primary compressive failure mode is micro buckling followed by kinking, at all temperatures. The existing micro mechanical model based on microbuckling and kinking for estimating the compressive strength has been modified to include temperature effects. The key model input parameters are temperature‐dependent resin tensile modulus and in‐plane shear strength. It is found that the modified model will predict the temperature‐dependent compressive strength in the temperature range of −20 to 150°C.Highlights Compressive strength decreased from 700 MPa at −20°C to 400 MPa at 150°C. Microbuckling followed by kinking failure was observed at all temperatures. In‐plane shear strength decreased from 44 MPa at −20°C to 27 MPa at 150°C. Resin tensile modulus decreased from 2.5 GPa at −20°C to 0.75 GPa at 150°C. Analytical model for compressive strength was extended for all temperatures.

The analysis provides the solution for the elasticity problem of a circular flat crack in a transversely isotropic elastic solid under uniform or linear shear stress distribution at the crack surface. This analysis, together with the published works <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5,6</sup> on circular cracks under normal stress, solves the problem of a circular crack under any uniform stress distribution at large distance from the crack. The result should be of interest in fracture mechanics. It may be of interest to remark that the solution presented here has provided valuable insight to solving the corresponding problem for the elliptical crack.

The applicability of ASTM Test Method for Shear Strength of Continuous Fiber-Reinforced Advanced Ceramics at Ambient Temperatures (C 1292) was investigated to determine the shear strength of one-dimensional and two-dimensional continuous fiber-reinforced ceramic composites. The advantages and disadvantages of the test method are addressed, and the effect of notch separation on the measured interlaminar shear strength by the compression of double-notched specimens are discussed. Experimental results are presented for the interlaminar and in-plane shear behavior of two-dimensional Nicalon™/SiC and the interlaminar shear strength of one-dimensional carbon/carbon composites both at room temperature and 1000°C. The effect of fiber coating thickness on the interlaminar shear strength of two-dimensional Nicalon™/SiC is also discussed.

The double lap shear specimen is examined in detail to serve as a baseline for further research on the behavior of composite to composite adhesive bonded joints. To examine the effect of laminate stacking sequence on crack initiation, adherents were prepared from three different laminates, [0]16T, [0/90]4s, [02/902]2s. The stress distributions along the bond interface of the specimens, predicted by a variational plane strain model, are presented. The crack initiation and its location were correlated with the stress analysis. The damage propagation modes were observed and characterized. In the case of unidirectional laminate, the crack (damage) found to occur and propagate in the composite; a few fiber diameter away from the bond interface.

Mechanical strength of the cement–bone interface is greater in shear than in tension

A thermal model for the thermoplastic shear instability in the machining of a titanium alloy (Ti-6Al-4V) is developed. It is based on the analysis of the shear-localized chip formation process and the temperature generated in the shear band due to various heat sources (primary, preheating, and image) in machining. The temperature in the shear band was determined analytically using the Jeager’s classical stationary- and moving-heat-source methods. Using Recht’s classical model of catastrophic shear instability (thermal softening vs strain hardening), the onset of shear localization was determined. The shear stress in the shear band is calculated at the shear-band temperature and compared with the value of the shear strength of the bulk material at the preheating temperature. If the shear stress in the shear band is less than or equal to the shear strength of the bulk material, then shear localization is imminent. The cutting speed at which this occurs is taken as the critical speed for the onset of shear localization, which continues at all speeds above this value. In the case of titanium alloys, this speed is rather low, indicating shear localization practically at all conventional cutting speeds. The effect of the depth of the cut on the onset of shear localization was also considered, as it may affect the heat transfer from the shear-localized region, i.e., between the segments in the chip, to the rest of the chip and preheating of the segment. For example, there can be a significant difference in the thermal aspects of shear localization in ultraprecision machining (where the depths of cuts are a few micrometers or less) compared to conventional machining (where the depths of cuts are several hundred micrometers). This is because of the differences in the distances between the segments as well as the energy inputs in each case.

This work investigates the fatigue behavior of satin fabric-woven carbon fiber-reinforced poly-ether-ketone-ketone (PEKK) laminates under low (20 Hz) and ultrasonic (20 kHz) testing frequencies using identical specimen geometries. Specimen designs across all orientations were based on modal, harmonic, static-structural, and buckling analyses to ensure comparable results. This design enables uniaxial tension–compression loading of woven carbon-fiber reinforced polymers (CFRPs) to fail in the gauge section without global buckling and ensures overlapping stress amplitudes between the two test systems. The maximum possible stress amplitudes of ultrasonic fatigue testing (UFT) are higher than the lowest stress amplitudes that cause failure in the conventional servo-hydraulic (SH) system. By using the anisotropy of composite laminates, this design was validated through tension–compression experiments on dogbone-shaped specimens with four fiber orientations: 0°, 15°, 30°, and 45°, using SH and UFT systems. Results comparing high-cycle fatigue (HCF) and very high-cycle fatigue (VHCF) behavior of angle-ply laminates indicate a strong dependence on fiber orientation. A comparison of self-heating and microscopic analysis between the two systems demonstrates the applicability of UFT for off-axis VHCF characterization of woven composites. Finally, shear stress-induced damage initiation in 0°fiber-oriented dog-bone-shaped specimens, as observed in this work and reported in the literature, is addressed as a multi-axial stress state problem by incorporating the resultant normal, transverse, and shear stresses into the Tsai–Wu formulation. • The VHCF strength for all off-axis orientations agrees well between two test systems. • Dog-bone shaped CF-PEKK specimen design can endure reversed fatigue without buckling. • Optimal pulse-pause ensures comparable CF-PEKK self-heating at 20 Hz and 20 kHz. • The VHCF damage in woven composites initiates at the surface under uni-axial loading.