Investigations of Cruciform Specimen Designs for Biaxial Tensile Testing of SMC

Abstract

This proceedings paper presents the investigation of different cruciform specimen designs for the characterization of Sheet Molding Compounds under biaxial loading. Biaxial tensile tests allow the investigation of damage evolution under multiaxial stress states, which is particularly interesting due to the different damage phenomena in composite materials. A key challenge is to find a suitable specimen shape, because typical cruciform specimens fail in the arms before damage occurs in the area of interest which is the area of the biaxial stress state in the center region of the specimen. For all of the introduced designs the stiffness degradation is analyzed more in detail and compared to that of a uniaxial bone specimen. For the best performing specimen which is reinforced by unidirectional reinforced tapes on the arms, the strain field is analyzed by finite element simulations, taking into account the mechanical properties of the different layers of the specimen. Especially in the center area and at critical points, strain concentrations and non-symmetrical strain distributions are analyzed and evaluated.

Advances in Cruciform Biaxial Testing of Fibre-Reinforced Polymers

“…Similarly, Lecompte et al [91] estimated the orthotropic elastic properties of a GFRP lamina by using an inverse FEM technique, minimising the difference between the strains obtained experimentally and numerically. Other studies following a similar scheme are the ones carried out by Schemmann and Lang et al [32,33,92]. These works are among the few that focus on studying unreinforced and continuous fibre-reinforced thermoplastic polymers.…”

“…Firstly, it should be highlighted the cost and space necessary to apply tensile and compressive loads in a controlled way in two perpendicular directions, added to the possible need to carry out measurements in those two load directions. Secondly, a control scheme is required to avoid the appearance of deflections or undesired shear loads, for which regulation schemes through closed loop and control of the midpoint displacement [30,32,33] are frequently utilised.…”

Numerical optimization-based design studies on biaxial tensile tests

“…Besides optimization, sensitivity studies on geometrical parameters of cruciform test specimens have been done using Finite Element analyses. 18 A number of different specimen geometries for performing biaxial testing of multiple alloys under elevated temperature conditions have been experimentally investigated by Abu-Farha et al 2 Basic experimental and simulative studies on ideal geometries for polymeric material specimens of biaxial tensile tests have been presented by Hartmann et al 19 Several cruciform specimen designs for testing sheet molding compounds have been investigated experimentally and numerically by Lang et al 20 and Schemmann et al 21 Geometry designs for increasing the measurable plastic strain rates have been presented by Hou et al 22 This brief literature survey underlines the continuing research interest in optimizing the shape and topology of cruciform biaxial tensile specimens.…”