Enhanced pure shear characterization of FRP using Tension-Compression testing methodology on cruciform specimens
Topic(s) : Experimental techniques
Co-authors :
Sergio HORTA MUÑOZ (SPAIN), María Del Carmen SERNA MORENO (SPAIN)Abstract :
Characterizing shear properties in fibre composite materials poses challenges in achieving pure and uniform shear stress states up to the failure point. Widely adopted standardized methods often limit their applicability to small strains, while shear response is highly non-linear. This study proposes a comprehensive analysis of the biaxial tension-compression (TC) test with cruciform specimens. Specifically, to determine the shear properties of a unidirectional carbon fibre-reinforced ply in material principal directions, the TC test is applied to symmetrical ±45° angle-ply laminates. Special emphasis is given to confirming the achieved shear state by comparing the results with other tests that also induce shear stress-strain states along the material principal directions. Moreover, the analysis of the experimental data is supported by finite element method simulations [1].
Critical to this investigation is the confirmation that the arms of the specimen, under uniaxial loading, exhibit no pseudo-ductile effects that could influence the measurement of the response in the pure shear loaded region. Then, the integration of Digital Image Correlation (DIC) during the test, coupled with numerical simulations, allows monitoring the full field of displacements and strains. This enables the verification of the presence or absence of a nonlinear response in various regions of the cruciform specimen. Regarding the shear dominated region, the stress–strain evolution reveals a linear stage succeeded by an inelastic region featuring significant shear distortion. During the linear stage, DIC precisely measures a pure and homogeneous shear strain state. Subsequently, DIC captures the initiation of a shear band at a 45° angle from the loaded directions, culminating in the final failure plane. These experimental evidences ensure the validity of the proposed testing methodology. Compared to other standardized shear characterization methodologies, the TC test allows to increase the failure shear strain by up to 40% by using a biaxial anti-buckling device [2] which prevents the appearance of instabilities in the arms of the specimen.
This research significantly advances our understanding of shear behaviour in composite materials, providing insights that extend beyond small deformations and contributing to more reliable material characterization methodologies. The findings have already contributed to a more accurate understanding of shear behaviour, as this methodology is already in the process of standardization, giving rise to a technical specification from the Spanish standardization organization UNE 0074:2023 [3].
Critical to this investigation is the confirmation that the arms of the specimen, under uniaxial loading, exhibit no pseudo-ductile effects that could influence the measurement of the response in the pure shear loaded region. Then, the integration of Digital Image Correlation (DIC) during the test, coupled with numerical simulations, allows monitoring the full field of displacements and strains. This enables the verification of the presence or absence of a nonlinear response in various regions of the cruciform specimen. Regarding the shear dominated region, the stress–strain evolution reveals a linear stage succeeded by an inelastic region featuring significant shear distortion. During the linear stage, DIC precisely measures a pure and homogeneous shear strain state. Subsequently, DIC captures the initiation of a shear band at a 45° angle from the loaded directions, culminating in the final failure plane. These experimental evidences ensure the validity of the proposed testing methodology. Compared to other standardized shear characterization methodologies, the TC test allows to increase the failure shear strain by up to 40% by using a biaxial anti-buckling device [2] which prevents the appearance of instabilities in the arms of the specimen.
This research significantly advances our understanding of shear behaviour in composite materials, providing insights that extend beyond small deformations and contributing to more reliable material characterization methodologies. The findings have already contributed to a more accurate understanding of shear behaviour, as this methodology is already in the process of standardization, giving rise to a technical specification from the Spanish standardization organization UNE 0074:2023 [3].