In this work, the applicability of the Iosipescu and off-axis test methods for the shear characterization of clear wood was investigated. Wood of maritime pine (Pinus Pinaster Ait.) was used. Iosipescu shear tests were carried out for oriented specimens in the three natural symmetry planes of wood (LR, LT and RT planes), whereas off-axis tests were performed only in the LR and LT planes. Finite element analyses were conducted in order to access the stress and strain fields in the test section of the specimens. It was found that the Iosipescu and off-axis tests provide different shear moduli values. It was also shown that the Iosipescu test gives lower and upper bounds of shear strengths, whereas the off-axis test gives only a lower bound, directly from the measured loads.

A comparison between the iosipescu and off-axis shear test methods for the characterization of Pinus Pinaster Ait

A detailed evaluation of the suitability of the Iosipescu specimen tested in the modified Wyoming fixture is presented. A linear finite element model of the specimen is used to assess the uniformity of the shear stress field in the vicinity of the notch, and demonstrate the effect of the nonuniform stress field upon strain gage measurements used for the determination of composite shear moduli. Based upon test results from graphite epoxy laminates, the proximity of the load introduction point to the test section and the material orthotropy greatly influence the individual gage readings, however, shear modu lus determination is not significantly affected by the lack of pure shear. Correction factors are needed to allow for the nonuniformity of the strain field and the use of the average shear stress in the shear modulus evaluation. The correction factors are determined for the region occupied by the strain gage rosette. A comparison of the strain gage readings from one surface of a specimen with corresponding data from moire interferometry on the opposite face documented an extreme sensitivity of some fiber orientations to eccentric loading which induced twisting and spurious shear stress-strain curves. The discovery of specimen twisting explains the apparently inconsistent shear property data found in the literature. Recommendations for improving the reliability and accuracy of the shear modu lus values are made, and the implications for shear strength measurement discussed.

An Evaluation of the Iosipescu Specimen for Composite Materials Shear Property Measurement. Ph.D. Thesis

Distributions of shear strains and strain states (triaxiality) were analysed for two in-plane shear test fixtures (Iosipescu and V-notched rail), using digital image correlation and numerical simulations. Three different polypropylene-based materials (two talc-filled compounds and one unfilled homopolymer) were tested. The three materials behaved differently in the shear tests. Most notably, cracks developed in tension near the notches for the particle-filled materials, while the unfilled homopolymer did not fracture. There were also differences between the materials regarding strain localisation between the notches, strain rates vs. strain level (for a given cross-head speed), thickness change in the sheared section, and triaxiality. The yield stresses in shear, uniaxial tension and uniaxial compression showed pressure sensitivity. At least for equivalent strain rates below 1 s−1, the strain rate sensitivity of the yield stress was approximately the same in these three stress states. The stress–strain curves obtained with the two methods were quite similar for these materials. There were some differences between the methods regarding the ease of mounting and aligning specimens, the complexity of specimen deformation patterns, and the uniformity of the shear strain distribution between the notches.

Shear Testing of Polypropylene Materials Analysed by Digital Image Correlation and Numerical Simulations

Linearly elastic finite element analyses were used to examine the effects of fiber orientation, notch angle and notch root radius on the stress distribution in Arcan specimens in order to optimize the specimen geometry for the unidirectional, fiber reinforced composite AS4/PEEK under shear and biaxial loadings. Two fiber orientations, three notch angles and five notch root radii were examined. A comparison between butterfly-shaped and circular S-shaped specimens was also made. For specimens with fibers running across the specimen from grip to grip (1-2 orientation), a 1340 notch angle was found to be the best choice due to superior stress uniformity along the gage section and minimum transverse normal stress along the notch flank. However, specimens with fibers running from notch to notch (2-1 orientation), required a 900 notch angle for optimum stress uniformity along the gage section and minimum transverse normal stress along the specimen notch. It was also found that, along the gage section, the larges...

Finite Element Analysis of the Arcan Specimen for Fiber Reinforced Composites under Pure Shear and Biaxial Loading

Polycrystalline graphites are widely used in the metallurgical, nuclear and aerospace industries. Graphites are particulated composites manufactured with a mixture of coke with pitch, and changes in relative proportions of these materials cause modifications in their mechanical properties. Uniaxial tension tests must be avoided for mechanical characterization in this kind of brittle material, due to difficulties in making the relatively long specimens and premature damages caused during testing set-up. On other types of tests, e.g. bending tests, the specimens are submitted to combined stress states (normal and transverse shear stresses). The Iosipescu shear test, is performed in a beam with two 90° opposite notches machined at the mid-length of the specimens, by applying two forces couples, so that a pure and uniform shear stress state is generated at the cross section between the two notches. When a material is isotropic and brittle, a failure at 45° in relation to the beam long axis can take place, i.e., the tensile normal stress acts parallel to the lateral surface of the notches, controls the failure and the result of the shear test is numerically equivalent to the tensile strength. This work has evaluated a graphite of the type used in rocket nozzles by the Iosipescu test and the resulted stress, ~11 MPa, was found to be equal to the tensile strength. Thus, the tensile strength can be evaluated just by a single and simple experiment, thus avoiding complicated machining of specimen and testing set-up.

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Assessement of tensile strength of graphites by the Iosipescu coupon test

The purpose of this paper is to compare the value of the shear modulus of an isotropic material (PMMA) obtained from both tensile and losipescu shear tests. A finite-element model is introduced to account for a nonuniform stress distribution in the losipescu coupon. A correction accounting for nonuniform strain values over the strain-gage section is also introduced. Rigorous statistical data processing leads to an estimation of the error between the moduli obtained by the two tests. Some points relevant to the losipescu test are reviewed, particularly concerning the sample preparation. Provided that a careful procedure is followed, excellent agreement is achieved between the shear moduli measured by the two methods.

A. Vautrin

Papers

The losipescu in-plane shear test: Validation on an isotropic material