Investigation of Quasi-Static and Dynamic Material Properties of a Structural Sheet Molding Compound Combined with Acoustic Emission Damage Analysis

Abstract

Sheet molding compounds (SMC) are discontinuously fiber-reinforced thermosets, attractive to the automotive industry due to their outstanding specific strength and stiffness, combined with a cost efficient manufacturing process. Increasingly important for structural components, a structural SMC-based improved resin formulation featuring no fillers is investigated in this study. The influence of fiber volume content, fiber length, and manufacturing induced fiber orientation on quasi-static and dynamic mechanical properties of vinylester-based SMC is characterized. Stiffness and strength increased with increasing fiber volume content for tensile, compression, and flexural loadings. Fiber length distribution did not significantly influence the mechanical properties of the material. The movement of the conveyor belt leads to an anisotropic fiber orientation and orientation-dependent mechanical properties. Acoustic emission coupled with machine learning algorithms enabled the investigation of the damage mechanisms of this discontinuous glass fiber SMC. The acoustic emission analysis was validated with micro computed tomography of damaged specimens. The dominant failure mechanisms of the SMC exposed to bending loading were matrix cracking and interface failure.

A convex anisotropic damage model based on the compliance tensor

“…Indeed, due to the convexity property of the Hookean elastic energy, it is possible to develop a purely hardening damage-mechanics modeling-framework, where localization does not become an issue. Very much, there are materials which show a purely damagehardening material response prior to sudden and brutal failure, e.g., Sheet Molding Compound (SMC) composites (Anagnostou et al, 2018;Fitoussi et al, 1996Fitoussi et al, , 1998 comprising an unsaturated polyester-polyurethane hybrid (UPPH) resin (Kehrer et al, 2018;Schemmann et al, 2018a;Trauth et al, 2017) reinforced by glass fibers (G€ orthofer et al, 2019;Meraghni and Benzeggagh, 1995;Schemmann et al, 2018c).…”

Recognition of Damage Modes and Hilbert–Huang Transform Analyses of 3D Braided Composites

“…Over a long service period, these composites inevitably experience damage and failure [2][3][4]. Benefiting from its dynamic, sensitive, real-time, and anti-interference characteristics, acoustic emission (AE) technology has been gradually applied to the detection of damage in composite materials [5]. Researchers have conducted many studies of the use of AE technology in damage detection in composite materials.…”

Editorial for the Special Issue on Discontinuous Fiber Composites

“…Schemmann et a. [1] designed various test specimens to measure the mechanical behavior of SMC under biaxial loading, and Trauth et al [2] studied the effect of volume fracture and SMC semi-finished charge manufacturing conditions on the mechanical properties of the molded parts. A variety of thermoplastic matrices and processes are also available for discontinuous fiber-reinforced composites.…”

“…The processing of discontinuous fiber-reinforced composites, such as mold filling in injection molding, or flow through the nozzle during fused filament fabrication, has a profound impact on the arrangement of the fibers within the finished part. As fiber filled polymers are shaped into the final part geometry, the fibers are not only oriented [2,3,[7][8][9][10][11], but they are also broken down [4] and agglomerated [12], resulting in highly anisotropic products. While the anisotropy can be beneficial, when the fibers are aligned in the direction of highest stresses, most design processes of discontinuous fiber-reinforced composites parts do not consider all aspects of the process-microstructure-property relationship.…”

“…While the anisotropy can be beneficial, when the fibers are aligned in the direction of highest stresses, most design processes of discontinuous fiber-reinforced composites parts do not consider all aspects of the process-microstructure-property relationship. Several papers in this issue relate mechanical properties to fiber microstructure [1][2][3]5,7,9,10] and the paper by Wang and Smith [10] relate the microstructure to rheological behavior. Not incorporating the effect of fiber microstructure can result in larger safety factors, which leads to higher weight than necessary, limiting the application of this class of materials.…”