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The interlaminar shear modulus of cardboards was measured using torsional vibration (TV) and flexural vibration (FV) methods. In the TV method, the sample widths were decreased during the tests, and the interlaminar and in-plane shear moduli were determined using the data obtained based on the different widths. By contrast, in the FV method, the resonance frequencies from the first to third FV modes were measured using samples of various lengths, and the interlaminar shear modulus and Young's modulus in the length direction were calculated using Timoshenko's vibration theory. In addition to the experiment, modal analyses based on the finite element (FE) method were performed, and the sample configurations used to accurately obtain the interlaminar shear modulus were experimentally and numerically investigated. The TV method did not allow the interlaminar shear modulus to be obtained appropriately because the vibration behavior often deviated from that theoretically derived by the TV equation. By contrast, the FV method allowed the interlaminar shear modulus to be obtained appropriately for a wide range of sample lengths. [ABSTRACT FROM AUTHOR]

Abstract: An inverse parameter identification technique has been proposed to determine the elastic interlaminar shear modulus of composite laminates. The technique involves minimising the difference between an experimentally measured and a numerically determined material response by varying the interlaminar shear modulus in the numerical model. As such, the ‘optimum’ interlaminar shear modulus can be found by using a relatively simple mechanical test. The inverse parameter identification technique using a modified Iosipescu shear test and three-point bend test was applied in the current study. Experimental investigations, numerical studies, as well as the development of a computer program were conducted to implement the proposed technique. An average elastic interlaminar shear modulus of 3.23GPa and 2.37GPa was obtained with the modified Iosipescu shear and three-point bend tests, respectively. These results are extremely promising as they are close to previously speculated values. It is acknowledged that a discrepancy of approximately 26.6% exists between the two results, however, a comprehensive explanation of this difference is provided. [Copyright &y& Elsevier]

Abstract: An inverse parameter identification technique using a modified Iosipescu shear test (MIST) has been developed for determining the viscoelastic interlaminar shear modulus of composite laminates. The main component of the technique involves minimising the difference between an experimentally measured and a numerically determined creep response at various elevated temperatures by varying the interlaminar shear modulus terms in the numerical model. Consequently, the ‘optimum’ model for the viscoelastic interlaminar shear modulus can be found at each temperature. These individual models are then combined to form a single ‘master curve’ for which a time-shift function and a Prony-series is fitted. In the present studies, Hexcel F593–18 plain weave pre-preg laminates were investigated. Experimental creep tests were conducted at various temperatures between 40°C and 150°C. Through the application of the inverse parameter identification technique, it was determined that the viscoelastic interlaminar shear moduli of the composite material can be effectively modelled by a nine-term Prony series and a third-order polynomial time-shift function. [Copyright &y& Elsevier]

A sensitivity analysis using finite element (FE) simulations was conducted as part of an overall attempt to develop a new and robust parameter identification method for determining the interlaminar shear moduli G13 and G23 of laminated composite materials. It is proposed that the new method will use an integrated experimental and numerical technique. Six different shear and bending tests were investigated numerically using three-dimensional FE models to determine their suitability for this integrated technique. The sensitivity of the potential tests to changes in the different material properties, especially the interlaminar shear moduli, G13 and G23, and the elastic modulus in the through-thickness direction, E3, was determined. It was discovered that several configurations within three of the six potential tests considered are suitable for the new proposed parameter identification method. This is based on the criteria that they are more sensitive to the interlaminar shear moduli than to other material constants. When manufacturing factors were considered, the two most suitable tests were identified for use in the new proposed method. [Copyright &y& Elsevier]

To investigate the mechanical degradation of the shear properties of glass fiber-reinforced polymer (GFRP) laminates in bridge decks under hygrothermal aging effects, short-beam shear tests were performed following the ASTM test standard (ASTM D790-10A). Based on the coupled hygro-mechanical finite element (FE) analysis method, an inverse parameter identification approach based on short-beam shear tests was developed and then employed to determine the environment-dependent interlaminar shear modulus of GFRP laminates. Subsequently, the shear strength and modulus of dry (0% Mt/M∞), moisture unsaturated (30% Mt/M∞ and 50% Mt/M∞), and moisture saturated (100% Mt/M∞) specimens at test temperatures of both 20 °C and 40 °C were compared. One cycle of the moisture absorption–desorption process was also investigated to address how the moisture-induced residual damage degrades the shear properties of GFRP laminates. The results revealed that the shear strength and modulus of moisture-saturated GFRP laminates decreased significantly, and the elevated testing temperature (40 °C) aggravated moisture-induced mechanical degradation. Moreover, an unrecoverable loss of shear properties for the GFRP laminates enduring one cycle of the moisture absorption–desorption process was evident. [ABSTRACT FROM AUTHOR]