Iosipescu Shear Test Method Research Articles

Evaluation of a modified Iosipescu shear test method for determining the shear properties of clear wood

A modified Iosipescu shear test method is proposed as an alternative for measuring the shear properties of clear wood. The method adopts four-point asymmetric loading procedure in the Iosipescu shear test but with the loading positions shifted to the neutral axis of the specimen. The original V-notched specimen is replaced by a combination of polyvinyl chloride blocks at two ends and a bow-tie-shaped wood specimen in the middle to provide a better stress pattern at failure. The measured shear strength and shear moduli are compared with results from compression test and off-axis tension test. Finite element analysis is also carried out to study the stress distribution in the wood specimen. Results show that the new shear test setup can provide close-to pure shear stress state in the specimen yielding better estimates of the shear properties of wood. The shear strength obtained by the new test setup is slightly lower than that from the off-axis tensile test which is probably due to the relatively thick specimen chosen in this study.

Experimental Study on Interlaminar Shear Properties of T300/BMI Composite Laminates

A modified test fixture to measure the shear properties of composite laminates was designed and manufactured based upon Iosipescu shear test method. Tests on interlaminar shear propertis of T300/BMI composite laminates were conducted according to ASTM D 5379 test standard. Interlaminar shear stress/strain curves and shear failure modes were obtained. The test results showed that the modified shear test fixture and test method were effective in measuring the shear properties of composite laminates.

Comparative Study of Locational Variation in Shear and Transverse Elastic Modulus of Buffalo Cortical Bone

The heterogeneous nature of bone material is responsible for locational variation in its mechanical properties whereas its anisotropic nature makes these properties to be directional. Cortical bone is considered to be weak in shear but weakest when a transverse tensile load is applied. In the present investigation transverse elastic modulus and shear modulus are evaluated at different locations of buffalo femoral bone diaphysis using uniaxial tensile and Iosipescu shear test method. The locational values of these mechanical properties obtained in the present study are also compared with the corresponding values for tibiae cortical bone. The values of elastic modulus and shear modulus were found to be maximum at the middle location and minimum at the lower location of bone diaphysis. Femoral cortical bone was found to be having higher values of these mechanical properties as compared to the tibiae cortical bone. The values of longitudinal shear modulus were observed to be higher as compared to the transverse shear modulus for buffalo cortical bone.

Studies on Locational Variation of Shear Properties in Cortical Bone with Iosipescu Shear Test

Bone material is very complex in nature due to its anisotropic and hierarchical structure. Bone is weaker in shear as compared to tension and compression therefore shear properties of bone material are important to find out. Many researchers have applied different techniques to find out shear properties of bone material but these techniques either require such type of bone specimens which are difficult to prepare or provides limited information about the shear properties. Iosipescu shear test method has been applied in the present work to find out locational variation in shear properties of cortical bone. This technique seems to be very effective for the case of bone material and require less effort as compared to the other techniques applied by the other researchers in the previous reports.

Efeito da degradação ambiental nas propriedades de cisalhamento de compósitos PPS/fibra de carbono

Os compósitos termoplásticos avançados são uma alternativa a compósitos termorrígidos em algumas aplicações aeronáuticas, devido a ganhos em propriedades. Dentre as matrizes termoplásticas, o PPS (poli sulfeto de fenileno) destaca-se devido às suas características estruturais. O objetivo deste trabalho é avaliar a influência do condicionamento ambiental sobre o comportamento de resistência ao cisalhamento de PPS / fibras de carbono. Por esta razão, amostras deste material foram condicionadas em solução salina, em banho higrotérmico e sob radiação UV. Após estes condicionamentos os corpos-de-prova foram avaliados quanto a sua resistência aos cisalhamentos interlaminar (ILSS) e Iosipescu e os resultados obtidos foram comparados. Quando comparado ao valor de cisalhamento interlaminar obtido do compósito não-climatizado (58,4 ± 1,9 MPa), os valores de cisalhamento interlaminar ILSS decaíram em torno de 14 e 3%, respectivamente, após banho higrotérmico e banho salino. Sob condicionamento por radiação UV houve um decréscimo de 2% após exposição por 300 horas, 11% após 600 horas e 9% após 900 horas. Já o laminado ensaiado pelo método Iosipescu teve uma tensão de cisalhamento no plano de 109,2 ± 0,4 MPa. Com condicionamentos, teve um decréscimo de 6% após banho higrotérmico e 12% após banho salino. A exposição à radiação UV provocou na resistência de cisalhamento no plano um decaimento de 6% para o condicionamento de 300 horas, 10% para o condicionamento de 600 horas e 14% para o condicionamento por 900 horas.

Influence of environmental conditioning on the shear behavior of poly(phenylene sulfide)/glass fiber composites

AbstractAdvanced thermoplastic composites are an alternative because of their ease of processing and storage. Poly(phenylene sulfide) (PPS) stands out among these materials because of its structural characteristics; for instance, it provides size, shape, and thermal stability, low moisture absorption, excellent chemical resistance, and good mechanical properties, including flexure, strength, and shear properties, compared to thermoset composites. Thus, the objective of this study was to evaluate the influence of environmental conditioning on the shear strength behavior of PPS/glass fiber composites. For this reason, first, some samples were treated to UV‐light exposure in a chamber. Other samples were immersed in seawater and hygrothermal baths simultaneously. They were tested with the interlaminar shear strength (ILSS) and Iosipescu shear test methods. The shear values obtained for the treated samples were compared against the dry sample values. For all samples tested with the ILSS and Iosipescu methods, the results indicate that the PPS/glass fiber composites presented a decrease in shear strength after they were submitted to hygrothermal and seawater solution conditioning. The moisture absorption was not uniform throughout the material, and wet conditioning induced strong matrix plasticization, which reduced the shear strength values of the laminates. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

Failure Investigation of Graphite/Polyimide Fabric Composites at Room and Elevated Temperatures Using the Biaxial Iosipescu Test

The biaxial and modified biaxial Iosipescu shear test methods were applied to determine the shear dominated, biaxial mechanical response of graphite/PMR-15 and graphite/Avimid-R woven fabric composites at room and elevated temperatures. Three different composite architectures were examined: T650-35 warp-aligned, 8-harness satin (8HS) fabric in a PMR-15 matrix, T650-35 warp-aligned, 8HS fabric in an Avimid-R matrix and T650-35 0°/90°, 8HS fabric in an Avimid-R matrix. Several biaxial Iosipescu tests were performed at room temperature under shear, shear-tension, and shear-compression loading conditions to characterize damage and obtain biaxial, shear dominated failure properties. Shear tests were also conducted at elevated temperatures approaching 316 °C to determine the effects of temperature on the shear strengths of the composites investigated. A nonlinear finite element analysis is briefly introduced to evaluate the effects of specimen sliding and geometric nonlinearities on the stress and strain distributions in the biaxial Iosipescu specimens. In addition, the effects of different loading block geometries on the stress distribution in the Iosipescu specimens subjected to biaxial loads were also investigated. Within this investigation, it was found that graphite/Avimid-R was more resistant to biaxial, shear dominated failure at room temperature in comparison to graphite/PMR-15. However, the graphite/PMR-15 composite system exhibited better shear strength properties at elevated temperatures above 232 °C. It was also found that the effect of compression along the notch root axis generated by the loading blocks did not affect the loads at failure.

The Iosipescu test method as a method to evaluate the tensile strength of brittle materials

Composite materials with varying toughness levels were tested using the Iosipescu shear test method. The failure modes were analyzed and classified into brittle, mixed or shear modes. It is shown that the tensile strength of the composites showing brittle failure can be determined directly from the load values obtained by the Iosipescu shear test. The advantages of the use of this test method in relationship to the common tensile or flexure test methods usually used to determine the tensile strength of brittle materials are discussed.

Effect of cement modulus on the shear properties of the bone–cement interface

Shear tests of the bone–cement interface were performed in vitro using two types of bone cement, standard poly(methyl methacrylate) (PMMA) and a reduced-modulus formulation with poly(butyl methacrylate) beads in a methyl methacrylate matrix (PBMMA). Tests of shear properties were also calculated on cancellous bone and on each cement alone. The tests were done using the Iosipescu shear test method which generates a pure shear force in a zero-moment section of the specimen. With this method, shear properties can be determined at specified locations throughout the specimen. Tests were performed across the entire interface region, specifically in the middle of the region of cement–bone interdigitation and at both the bone and cement ends of that region. Ultimate shear strengths and shear moduli were calculated. The shear modulus of the PBMMA is less than 3% that of PMMA. The strength and modulus of cancellous bone had a direct relation to the apparent density of the bone, as did the strength and modulus of the bone–composite interface and the composite region. Strength and modulus were dictated by the bone at the bone–composite interface, and by the cement at the cement–composite interface. Through the composite region, the stiffer of the two materials in the composite determined the shear properties. Reduced-modulus bone coment substantially decreases the interfacial shear stresses at the bone–cement interface which should decrease the rate of resorptive bone remodelling at this interface.

Experimental Assessment of Four Composite Material Shear Test Methods

Abstract Four ASTM standard shear test methods for characterizing composite materials were experimentally investigated: the short beam shear (ASTM D 2344), Iosipescu shear (ASTM D 5379), axial tension of a [±45]ns laminate (ASTM D 3518), and two-rail shear (ASTM D 4255). Six composite material systems were utilized: two thermoset matrix composites; S2 glass/3501-6 epoxy and AS4 carbon/3501-6 epoxy; and four thermoplastic matrix composites, S2 glass/polyetherketoneketone (PEKK), AS4 carbon/PEKK, E-glass/J2 polyamide and AS4 carbon/J2 polyamide. The results obtained for both shear strength and shear modulus indicate that the various methods each have limitations and inherent inaccuracies, with no one method being clearly superior to the others in all aspects. However, the Iosipescu shear test method does exhibit a number of particularly favorable characteristics.

Material Characterization of Pultruded Laminates and Shapes

This paper discusses the material characterization of wide flange pultruded structural shapes (E-glass, Vinylester). The material was subjected to three loading conditions: tension, shear, and bending. Coupon samples were obtained from web and flanges of the I-section for tension and shear tests. Tensile properties were obtained from rectangular coupons with end tabs loaded in tension to failure. Shear properties were obtained from two different test methods: Iosipescu shear test method and torsion of rectangular samples. Experimentally determined material properties were compared to analytical predictions based on micro and macromechanics. Micromechanical models are used for the prediction of individual laminae (roving layers, continuous strand mat, nexus veils) properties. Classical lamination theory (CLT) is then used to predict the laminate properties. In addition, I-beams were tested in bending to evaluate their response and the experimental results were compared to predictions using Mechanics of Laminated Beams (MLB) approach. Results indicate a good correlation between experimental data and theoretical predictions, showing that the properties of pultruded composites can be predicted with sufficient accuracy. The superiority of the torsion test for determination of in-plane shear stiffness is demonstrated.

Robust Design of the Iosipescu Shear Test Specimen for Composites

Abstract For the purpose of improving the accuracy of the Iosipescu shear test method, researchers have been interested in analyzing the uniformity of shear stress distribution along the notched cross section for different design configurations of specimens made of various materials. But a one-factor-at-a-time approach cannot lead to a full understanding of the shearing behavior. The statistical design of experiments based on finite element models is employed here to characterize impacts of main effects and interactions among various design factors on the uniformity of shear stress distribution along the notched cross section for two kinds of unidirectional laminae with different orthotropy: Boron/Al (boron-fiber-reinforced aluminum) and Gl/Epoxy (glass-fiber-reinforced epoxy). It is shown that (a) the notch radius and height of a specimen are significant factors, (b) the notch angle is also significant, and 90° is better than 110° in reducing the variation of shear stress distribution, and (c) some two-factor interactions are influential.

Accurate and Precise Fabrication of Iosipescu Shear Test Specimens

Abstract The experimental measurement of the shear modulus and shear strength has been of special interest to the materials and composites community for a number years. In recent years, the Iosipescu shear test method has become popular and widely used. The most widely used test fixture is the Modified Wyoming test fixture which requires a specific and accurately fabricated specimen. To date, the methodology to fabricate and inspect these specimens has been left to the discretion of the individual investigators. This technical note presents a suggested methodology for the accurate and precise fabrication of Iosipescu shear test specimens. Dimensional data and the associated error from specimens fabricated are presented as verification of the methodology.

The application of the iosipescu shear test to structural adhesives

AbstractThe Iosipescu shear test method, adapted for adhesives, was used to evaluate shear stress–strain properties of five epoxy‐based film adhesives. The shear strength of some adhesives, determined by this technique, was found to differ greatly from that determined by either lap shear and/or thick adherend tests. Accurate measurements of the adhesive bond‐line deformation enabled evaluation of the adhesive elastic and plastic properties as well as the calculation of shear modulus. A high‐speed video camera was employed to augment observation on the joint deformation.

The Iosipescu shear test method as used for testing polymers and composite materials

AbstractThe Iosipescu shear test, developed initially in the 1960s for use with homogeneous, isotropic structural materials such as metals, has been adapted during the past ten years for use with composite materials. Much of this development work has taken place at the University of Wyoming, where a very efficient test fixture configuration has been developed, and extensive test results have been generated. Many other research groups have also adopted the test method during the past five years. As a result, the American Society for Testing and Materials (ASTM) is presently in the final stages of making the Iosipescu shear test an ASTM standard. The test method is described and its range of applications indicated, including examples of typical data.

Shear Properties of Pultruded Glass FRP Materials

The in‐plane shear modulus and the in‐plane shear strength of pultruded glass fiber reinforced plastic (FRP) materials were measured using the Iosipescu shear test method. Material specimens, in coupon form, were cut from the webs and flanges of commercially produced polyester and vinylester wide‐flange pultruded beams. The experimental testing procedure is described, and data reduction methods needed to define the shear modulus and the shear strength from the nonlinear stress‐strain curves are discussed. A new method to obtain the in‐plane shear modulus directly from load‐displacement data is proposed. Shear modulus predictions using the proposed method are compared with those obtained from the stress‐strain data.

Current Status of the Iosipescu Shear Test Method

During the past several years, considerable study of the Iosipescu shear test method has been conducted by a number of investigators, including the present authors. Several dif ferent test fixture designs have been developed, and variations of the specimen size and notch configuration have been considered. Materials with properties ranging from iso tropic to highly orthotropic have been tested. The response of such materials has also been predicted using finite element techniques, and attempts have been made to correlate these predictions with available experimental data.

In-Plane and Interlaminar losipescu Shear Properties of Various Graphite Fabric/Epoxy Laminates

The Iosipescu shear test method was used to measure the in-plane and interlaminar shear properties of four T300 graphite fabric/Fiberite 934 epoxy composite materials. Weave geometries tested included an Oxford weave, a 5-harness satin weave, an 8-harness satin weave, and a plain weave with auxiliary warp yarns. Both orthogonal and quasi-isotropic layup laminates were tested. In-plane and interlaminar shear properties were obtained for laminates of all four fabric types. Overall, few differences in shear properties attributable to the fabric weave pattern were observed. However, the auxiliary warp material was significantly weaker and less stiff in interlaminar shear parallel to its fill direction.