Morphology-induced fatigue crack arresting in carbon fibre sheet moulding compounds

Abstract

Carbon Fibre Sheet Moulding Compounds (CF-SMCs) are tow-based composite materials. Interrupted fatigue tests, combined with computed tomography, were performed here to investigate the damage mechanisms in high in-mould flow CF-SMC.The tow-based microstructure created obstacles for fatigue damage propagation, increasing the CF-SMC's resistance against cyclic loading. Failure is shown to nucleate inside the tows, but inter-tow crack propagation tends to be hindered by the presence of the other tows. Tows oriented perpendicularly to the initial fatigue crack stop the crack itself, showing an intrinsic crack arrest mechanism. Additionally, pre-existing manufacturing cracks or voids do not propagate at all. As a result, flatter slopes of the SN diagrams were observed for CF-SMC than for other carbon or glass fibre composites with short, long and even continuous fibres.

Weld lines in tow-based sheet moulding compounds tensile properties: Morphological detrimental factors

“…Although the void content was higher than in the weld line-free specimens, their size never exceeded 0.5 mm. This size is comparable to the defects shown in [11] and [40], where it was shown to not affect the static nor the fatigue material failure. For one of the HF-O specimens considered, the void content was similar: VoxTex measured a 0.06% void content in the scan centred in the weld line, and 0.01% and 0% in the two adjacent scans (see Table 3).…”

Static and fatigue behavior of a carbon‐fiber SMC‐R composite under combined tensile and shear stresses

“…Fatigue test results presented in Figure 7 show large scatter in fatigue life, which can be attributed to variations in fiber orientation and fiber distribution in the material. Similar observation has been made by several investigators [12,14,15,17,18] regarding scatter in the fatigue data of compression molded carbon fiber SMC-R composites. In this section, statistical analysis of fatigue data were conducted to predict the fatigue performance of the material.…”

Evaluation and Modeling of Tensile Properties of Chopped Carbon Fiber Tapes Reinforced Thermoplastics of Different Tape Thicknesses

“…Shah et al developed a three-dimensional (3D) finite element modeling method to simulate the tensile strength and stiffness of CF-SMCs while taking into account the overlapping of the embedded sheets [12]. Martulli et al managed to link the fiber flow and internal geometry irregularities during the fabrication process with the mechanical properties of CF-SMCs [13][14][15] and verified the performance of thick-walled components fabricated with CF-SMCs [16]. Our group at the University of Tokyo studied the mechanical properties and internal geometries of CF-SMCs with ultrathin sheets (44 μm) through simulations [17][18][19][20] and compared the results with those for CF-SMCs with thicker sheets (150 μm in general).…”