An integrated computational materials engineering framework to analyze the failure behaviors of carbon fiber reinforced polymer composites for lightweight vehicle applications

Abstract

A bottom-up multi-scale modeling approach is used to develop an Integrated Computational Materials Engineering (ICME) framework for carbon fiber reinforced polymer (CFRP) composites, which has the potential to reduce development to deployment lead time for structural applications in lightweight vehicles. In this work, we develop and integrate computational models comprising of four size scales to fully describe and characterize three types of CFRP composites. In detail, the properties of the interphase region are determined by an analytical gradient model and molecular dynamics analysis at the nano-scale, which is then incorporated into micro-scale unidirectional (UD) representative volume element (RVE) models to characterize the failure strengths and envelopes of UD CFRP composites. Then, the results are leveraged to propose an elasto-plastic-damage constitutive law for UD composites to study the fiber tows of woven composites as well as the chips of sheet molding compound (SMC) composites. Subsequently, the failure mechanisms and failure strengths of woven and SMC composites are predicted by the meso-scale RVE models. Finally, building upon the models and results from lower scales, we show that a homogenized macro-scale model can capture the mechanical performance of a hat-section-shaped part under four-point bending. Along with the model integration, we will also demonstrate that the computational results are in good agreement with experiments conducted at different scales. The present study illustrates the potential and significance of integrated multi-scale computational modeling tools that can virtually evaluate the performance of CFRP composites and provide design guidance for CFRP composites used in structural applications.

Introduction

With the growing attention on energy conservation and environmental protection, lightweight design for automobiles is becoming increasingly attractive in the automotive industry. Generally speaking, material replacement, structural optimization, and application of new manufacturing technology can be adopted in the lightweight design process, among which material replacement is arguably the most effective approach [1]. Carbon fiber reinforced polymer (CFRP) composites, with a density of 1.55 g/cm³ and a tensile strength of up to 2000 MPa along the fiber direction, stand as one of the most promising classes of materials to replace the engineered metals for automotive structural components. In particular, chopped carbon fiber sheet molding compound (SMC) and woven composites have great potential in automotive manufacturing due to their excellent mechanical performance, moderate cost, and easier fabrication compared to unidirectional (UD) CFRP composites [[2], [3], [4]]. In order to fully exploit the potential of these CFRP composites, we need to target increasing the accessibility of CFRP component designs, improving the robustness of initial designs, and most importantly, reducing the development to deployment lead time of CFRP components. These targets will eventually help mitigate greenhouse gas emissions from passenger vehicles and improve national energy independence [5].

The typical material design (or replacement) cycle consists of appropriate material selection followed by component size, shape design, and optimization [6]. In woven and chopped SMC CFRP composites, material selection also involves the size of representative element selection at the microstructure level. For instance, changing the size and/or angle of fiber tows for woven composites or changing the chip orientation for SMC composites significantly alter the anisotropic behavior of the material as well as its failure mechanisms, which in turn influence failure strength and fracture toughness of the material [3]. Thus, material design is not only limited to the size and geometry of constituents but also closely connected to the microstructural design. Traditionally, characterization of materials is done by carrying out expensive and time-consuming material tests to establish stiffness (elastic modulus) as well as strength properties in all material coordinates. With the advancements in computational materials science and engineering as well as multi-scale modeling, the “validation through simulation” approach has been increasingly adopted to decrease the time and cost of applying new materials to automotive components. Integrated Computational Materials Engineering (ICME) is the integration of materials information captured through computational tools with engineering product performance analysis and manufacturing process simulation [7]. This concept was first described by the U. S. National Materials Advisory Board Committee in 2008. Since then, ICME has become a fast-growing discipline within materials science and engineering and has been successfully employed in the design of metallic metals [[8], [9], [10]]. Compared to advanced metallic systems, the CFRP composites have the unique features of anisotropic and heterogeneous multi-scale microstructures and even larger variations in the material properties induced by the unique injecting/compression molding processes. Currently, there still exist two major challenges in developing ICME tool for CFRP composites: (1) development of high fidelity computational models; and (2) integration of the validated models and computational tools into one automated workflow so that the material processing, microstructure, and component structure can be optimized simultaneously [11].

In line with the overarching goal of ICME to reduce the time and the cost in the discovery and development of novel CFRP composites structures, multi-scale computational models have been established and embraced in our previous work and those of other researchers [[12], [13], [14], [15], [16], [17], [18], [19], [20], [21], [22], [23], [24]]. A majority of those models deliver the concerned information embedded in equations and parameters from lower-scale simulations to higher-scale, which is termed as the bottom-up hierarchical approach [17]. These previous studies on multi-scale model development have addressed the first challenge to a large extent. The primary objective of the present work is to address the second challenge, i.e., to integrate the multi-scale computational models and demonstrate an ICME framework of CFRP composites for lightweight vehicles, with a particular focus on three types of widely-used thermoset epoxy based CFRP composites in structural parts: long fiber UD composites, chopped short fiber SMC composites, and woven composites.