45 Flexure Test for Measurement of In-Plane Shear Modulus

Abstract

A new method to obtain the in-plane shear modulus GLT for unidirectional oriented composite materials is proposed. The method is based on an original analytic way for calculating middle point displacement in a 3-point flexure test. The bending–twisting coupling effects in such a test induce the lift-off of the specimen at the fixture supports for some geometrical conditions. Thereby, contact points are located at two opposite points of the specimen. Consequently, new bending moments along the width of the specimen and twisting moments appear. By supposing resultant moments and shear forces per unit length are uniformly distributed, these distributions are calculated for static conditions along longitudinal and transverse cross sections of the specimen. After having expressed strain energy as a function of resultant moments and resultant shear forces per unit length, Second Castigliano’s theorem is applied in order to calculate the middle point displacement. No similar analytic way has been encountered in classical laminated beams theory or in classical laminated plates theory. The displacement obtained in this work and the one obtained from classical laminated beams theory are particularised to the case of 45 fibre orientation. GLT expressions have been derived from those displacement expressions in three ways: two of them from the solution of this work, not considering and considering shear effects, respectively, and the third one from displacement obtained from classical laminated beams theory. Experiments have been made for different geometric conditions in order to test the influence of geometric parameters in experimental results. For span-to-width ratios up to two, the values obtained are quite constant and agree well with the in-plane shear modulus value obtained by the material manufacturer using 45 tensile test.

Off-axis Flexure Test: A New Method for Obtaining In-plane Shear Properties

“…Five fiber orientation angles and ten different spans were used for the experimental work. The method of obtaining the in-plane shear modulus in [1] was also generalized for any fiber orientation angle in [3].…”

Material parameter identification for vacuum infusion manufactured components

“…The computing of the shear modulus G 12 according to the ASTM standards shows no significant difference between the two tests. The flexure test proposed by Mujika [3] shows a difference of 22% respect the other two tests.…”

“…The ultimate shear strain was not compared, due to a premature failure of the strain gages. Observing the the shear modulus of the 45° tensile test and comparing it with the method proposed by Mujika [3], a relative error of 22% is found. Considering the value obtained only as an approach, the error may be compensated with the advantage of not requiring strain gages or transducers.…”

“…This method proposed by Mujika [3] consist on a +45° laminated coupon loaded on a three point testing device. The author uses three mathematical formulations described in detail in the article.…”

“…Proper determination of the mechanical properties of the material is fundamental to improve the accuracy of the simulations. A wide variety of mechanical tests exist to determine these properties, in this study in-plane quasi-static mechanical tests are performed based on recommendations found in [1][2][3][4].…”