Abstract

In the automotive industry, being lightweight has become an important design factor with the enhancement of environmental regulations. As a result, many studies on the application of composite materials are in progress. Among them, interest in carbon materials, such as carbon sheet molding compound (C-SMC) and carbon-fiber-reinforced plastic (CFRP), which have excellent strength and stiffness, is increasing. However, CFRP is a material that makes it difficult to secure economic feasibility due to its relatively high manufacturing costs and limited mass production, despite its excellent mechanical strength and durability. As a result, many studies have been conducted on C-SMC as an alternative carbon composite material that can be easily mass-produced. In this regard, this study intended to conduct a study on evaluating the fatigue strength of C-SMC and CFRP among mechanical properties due to the lack of clear failure criteria for fatigue design. We investigated the tensile and fatigue strengths of C-SMC and CFRP, respectively. In the case of C-SMC, the mechanical strength tests were conducted for two different width conditions to evaluate the cutting effect and the machining methods to assess the effects of the edge conditions. To evaluate the fatigue failure assessment criteria, the stiffness drop and elastic modulus degradation criteria were applied for each fatigue test result from the C-SMC and CFRP. The results confirmed that the rationality of the failure criteria in terms of the stiffness drop and the application of the fatigue life prediction of C-SMC based on elastic modulus degradation demonstrated promising results.

Highlights

  • Carbon-fiber-reinforced plastic (CFRP) has excellent strength and stiffness

  • When loading is applied to carbon sheet molding compound (C-SMC), each boundary acts as a crack initiation site, which leads to more frequent crack initiations compared to CFRP

  • CFRP consists of a fiber matrix that has specific directionality, which has different mechanical properties depending on the directionality

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Summary

Introduction

Carbon-fiber-reinforced plastic (CFRP) has excellent strength and stiffness It can be lightweight, making it suitable for the manufacture of simple feature parts for automobiles, and is currently being applied in various ways [1]. C-SMC is a fiberglass-reinforced thermosetting material that has been applied to automobile production for a long time and can be mass-produced It has excellent lightweight realization and durability. Studies have been conducted on the fatigue life of the composite, such as failure criteria of the stiffness drop and fatigue damage accumulation [10,11,12,13,14,15]. Even in recent studies, fatigue life prediction by applying the degradation of the elastic modulus according to the stiffness reduction and damage of the composites were being made. A new failure criterion for each material was proposed based on the fatigue life estimation

Preparation of Test Specimen
Effect of the Edge Fabrication in Fatigue Life
Comparison of the Fatigue Lives of C-SMC and CFRP
Fatigue Life Prediction based on the Degradation of Elastic Modulus
Conclusions
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