Abstract
Short fiber reinforced plastics (SFRPs) have excellent moldability and productivity compared to continuous fiber composites. In this study, thermoelastic stress analysis (TSA) was applied to detect delamination defects in short carbon fiber reinforced plastics (SCFRPs). The thermoelastic temperature change ΔTE, phase of thermal signal θE, and second harmonic temperature component ΔTD were measured. In the fatigue test of SCFRP, it was confirmed that changes in ΔTE, θE, and ΔTD appeared in the damaged regions. A staircase-like stress level test for a SCFRP specimen was conducted to investigate the generation mechanism of the ΔTD. The distortion of the temperature change appeared at the maximum tension stress of the sinusoidal load—and when the stress level decreased, the temperature change returned to the original sinusoidal waveform. ΔTD changed according to the change in the maximum stress during the staircase-like stress level test, and a large value of ΔTD was observed in the final ruptured region. A distortion of the temperature change and ΔTD was considered to be caused by the change in stress sharing condition between the fiber and resin due to delamination damage. Therefore, ΔTD can be applied to the detection of delamination defects and the evaluation of damage propagation.
Highlights
Short fiber reinforced plastics (SFRPs) have received much attention due to their excellent moldability and productivity, as compared to continuous fiber composites
In Area c-2, a distortion of temperature change was observed at the maximum tension from the early stage of the fatigue test, and the 2f/1f value showed a similar change according to the increase and decrease of the maximum stress in the fatigue test
The temperature change under cyclic loading was measured for shortfiber-reinforced short carbon fiber reinforced plastics (SCFRPs) composites
Summary
Short fiber reinforced plastics (SFRPs) have received much attention due to their excellent moldability and productivity, as compared to continuous fiber composites. Belmonte et al [2,3] presented the influence of the fiber volume fraction on the damage mechanism in a short glass fiber. Fragoudakis [4] discussed the effect of the fiber orientation around geometric discontinuities in glass fiber reinforced plastic (GFRP) and presented an important topic for the manufacturing and design against failure of GFRP laminated structures. Nondestructive evaluation techniques using infrared thermography (thermographic NDT) have been effectively employed for the detection of delamination in FRPs. The thermographic NDT technique based on the thermal insulation effect of the delamination defect was applied to the NDT of composite materials. Maldague et al [8] developed pulse-phase infrared thermography for composite materials
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