1、CAE Design and Failure Analysis of Automotive CompositesOther SAE books of interest: Design of Automotive Composites By Srikanth Pilla and Charles Lu (Product Code: PT-164) Engineered Tribological Composites By Roy Cox (Product Code: R-401) Automotive Carbon Fiber Composites By Jackie D. Rehkopf (Pr
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3、Design and Failure Analysis of Automotive Composites Y . Charles Lu and Srikanth Pilla Warrendale, Pennsylvania, USA Copyright 2015 SAE International eISBN : 978-0-7680-8168-8Copyright 2015 SAE International. All rights reserved. No part of this publication may be reproduced, stored in a retrieval s
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9、1.877.606.7323 (inside USA and Canada)+1.724.776.4970 (outside USA) Fax: +1.724.776.0790v Table of Contents Introduction . 1 Design and Failure Analysis of Composites: Static l oading 11 Virtual Coupon Testing of Carbon Fiber Composites for Application in Structural Analysis (2014-01-0809)13 Multi-S
10、cale Modeling of an Injection Over-Molded Woven Fabric Composite Beam (2014-01-0961)19 Significance of Virtual Prototyping in Design of Composite Structures for Automobiles (2014-28-0031) .29 City Vehicle XAM 2.0: Design and Optimization of the Composite Suspension System (2014-01-1050) .35 Stress A
11、nalysis and Lay-Up Optimization of an All-Composite Pick-Up Truck Chassis Structure (2004-01-1519) 45 Design and Failure Analysis of Composites: Dynamic and Impact l oading . 57 Fatigue Life Simulation on Fiber Reinforced CompositesOverview and Methods of Analysis for the Automotive Industry (2012-0
12、1-0730) 59 Modeling and Simulating Progressive Failure in Composite Structures for Automotive Applications (2014-01-0962)69 Crash Modeling of High-Pressure Wet Wound Composite Vessels (2011-01-0016) .75 Investigation of Crashworthiness of Structural Composite Components in Frontal and Side NCAP Test
13、s (2013-01-0650) .91 Design Optimization of Hybrid Body-in-White (2013-01-0970) 107 Design and Failure Analysis of Composites: Blast l oading 115 Designing Composite Vehicles Against Blast Attack (2007-01-0137) 117 Innovative Composite Structure Design for Blast Protection (2007-01-0483) .125 About
14、the Editors 1331 Introduction Composites are extensively used in applications that need outstanding mechanical properties combined with weight savings. Composite materials possess superior properties because of their unique microstructure. A composite is a material system that consists of two or mor
15、e separate materials combined in a macroscopic structural unit. Unlike traditional materials (such as metals, ceramics, and polymers), whose microstructures are relatively fixed, composites are highly tunable in terms of microstructure and mechanical properties. As a result, composites are a desirab
16、le combination of the best properties of the constituent phases: they can be strong and lightweight at the same time. For example, carbon fiber composites can be more than 10 times stronger and 80% lighter than steels. With such extraordinary properties, composites have become the top choice for pro
17、ducing lightweight vehicles 1-1, 1-2, 1-3, 1-4, 1-5, 1-6, 1-7, 1-8. The benefits of composites go far beyond weight savings. Polymer matrix composites have great potential for part integrations, which will result in lower manufacturing costs and faster time to market. The composite parts can have mu
18、ch smaller tooling costs than do metal ones. Composites also have much better corrosion resistance than metals and are more resistant to damage, such as dents and dings, than aluminums. Polymer composites possess superior viscoelastic damping and thus provide the vehicles with improved noise, vibrat
19、ion, and harshness (NVH) performance. Composites also have a high level of styling flexibility in terms of deep drawn panel, beyond what can be achieved with metal stampings. Finally, composite materials can possess multifunctional (mechanical, thermal, electrical, and magnetic) properties by integr
20、ating various functional components into the polymer matrices. The so-called multifunctional or smart composites provide significant benefits to the vehicles when compared with traditional materials, which only have monotonic properties. Although the benefits of composites are well recognized, the u
21、se of composites in the automotive industry has faced some technical challenges. One major technical challenge has been the lack of knowledge in composites design. Traditionally, the automotive sector has designed structural components by using isotropic materials, such as steels, aluminums, and pla
22、stics. The basic material properties necessary to the design of a homogeneous structure are Youngs modulus (E), Poissons ratio (n), and failure strength (s f ). These properties for common materials, such as steel and aluminum, are readily available in materials handbooks and online resources, makin
23、g the overall design process of a structural component composed of an isotropic material relatively simple. In comparison, the design of structures involving anisotropic, composite materials is more challenging and complicated. A composite material is anisotropic in nature; that is, the properties a
24、t a point vary with direction of the reference axes and are associated with the scale. The basic material properties necessary to the design of a composite structure are the average properties of an individual lamina. Unlike conventional isotropic materials whose properties (E, n) are available in v
25、arious data sources, the properties of the lamina for a composite system cannot be readily found. The primary reason is that those properties are dependent upon the fiber volume fractions. Even for the same composite system, such as the carbon fiberepoxy composite, the basic lamina properties vary d
26、ramatically due to the amount of fibers used in the system. Therefore, it would be very difficult to establish a comprehensive composite material property database. The other major technical challenge in using composite materials is the lack of effective design tools,(i.e., the computer-aided engine
27、ering CAE tools). Although the automotive sector has been routinely using CAE methods for various structural analysis (static, dynamic, durability, noise and vibration, etc.), the practices have mostly involved isotropic materials. For isotropic materials, there are many choices of CAE software, and
28、 the precision and accuracy of the computational models have significantly increased over time. However, for anisotropic, fiber composite materials, few CAE software exists that is capable of composite modeling. There is also a lack of sufficient, rigorous models to simulate the sophisticated failur
29、e process of composite structures. This book focuses on the latest use of CAE methods in design and failure analysis of composite materials and structures. It begins with a brief introduction to the design and failure analysis of 2 composite materials and then presents some recent, innovated CAE des
30、ign examples of composite structures by engineers from major CAE developers and automobile original equipment manufacturers (OEMs) and suppliers. Design of Composite Structures Fiber composites are typically used in flat, laminate forms. Therefore, the analysis of mechanical behaviors of composites
31、generally follows the so-called classical lamination theory 1-9, 1-10. As seen in Figure 1.1, a laminate is made of multiple layers of unidirectional composites at various orientations. Each single layer is referred to as a ply or lamina. A laminate is thin, with its plane dimensions much larger tha
32、n its thickness. The x-y plane that is equidistant from the top and bottom surfaces of the laminate is called the mid-plane or mid-surface, and this mid-surface may be used to represent the entire laminate. Figure 1.1 The use of a mid-surface for the analysis of a laminate composite. For structural
33、calculations, it is often required to know the stiffness matrix, Q laminate , of the laminate, with which the forces and moments (N and M) can be related to the strain and curvatures ( e and k) (Equation 1). N M= Q laminate Equation (1) The overall process for obtaining the laminate stiffness matrix
34、 (Q laminate ) is illustrated in Figure 1.2, which shows that the laminate stiffness matrix (Q laminate ) is computed from the individual lamina stiffness matrix Q ply (Equation 2 and Equation 3). The individual lamina stiffness matrix in the material coordinate Q 12is calculated from the five funda
35、mental engineering constants (E 1 , E 2 , G 12 , n 12 , n 21 ) of the lamina (Equation 4), and finally the fundamental engineering constants of the lamina are directly computed from the properties of the constituents, fiber and matrix (Equation 5).Figure 1.2 Flowchart for the calculation of the stif
36、fness matrix of a laminate composite.3Q= AAABBB AAABBB AAAB laminate xx xy xs xx xy xs yx yy ys yx yy ys sx sy ss s sx sy ss xx xy xs xx xy xs yx yy ys yx yy ys sx sy ss sx BB BBBDDD BBBDDD BBBDD s sy ss D Equation (2) where A, B, D are defined as BQ (Z -Z ) ij ij k k 2 z-1 2 k n = = 1 2 1 DQ (Z -Z
37、) ij ij k k 3 z-1 3 k n = = 1 3 1 AQ (Z -Z ) ij ij k kk -1 k=1 n = The individual lamina stiffness matrix in the global coordinate Q xy is further calculated from the individual lamina stiffness matrix in the material coordinate Q 12 : Q= TQ T xy 12 TEquation (3) where T is the transformation matrix
38、 and Q 12 is the individual lamina stiffness matrix in the material coordinate (1, 2).Equation (4)In Equation 4, E 1 , E 2 , G 12 , n 12 , n 21 are the five fundamental engineering constants of the lamina. Those constants come directly from the properties (modulus, Poissons ratio, and volume fractio
39、ns) of the composite constituents, fiber and matrix (Equation 5). Q EE EE G 12 1 12 21 21 1 12 21 12 2 12 21 2 12 21 1 11 0 11 0 00 = 2 2 4E 1= E f V f + E m V m n 12= n f V f+ n m V m E 2= E f E m /(E f V m+ E m V f ) G 12= G f G m /(G f V m+ G m V f )Equation (5)Failure Analysis of Composite Struc
40、tures The failure of an isotropic material may be characterized by the yield strength ( s y ) and/or the ultimate tensile strength ( s f ). In a similar analogy, the failure of a laminate composite may be defined as the initial failure (first ply failureFPF) and/or the ultimate failure (ultimate lam
41、inate failureULF). To determine the FPF, the stress analysis is conducted on a laminate under given loading conditions, and the state of stress in each individual ply is computed. A laminate is considered failed when the first layer (lamina) in the structure has failed. Numerous theories for lamina
42、failure exist, which can be generally categorized into the following two groups: 1. Noninteractive theories, in which the failure is determined by a criterion that consider the stress in a particular deformation mode with corresponding strength. 2. Interactive theories, in which the failure is deter
43、mined by a criterion that includes all stress components and is applicable to all failure modes. An example of noninteractive theories is the MLT (Matzenmiller, Lubliner, and Taylor) failure criterion, which has been implemented in CAE software such as LS-DYNA. In this model, the contribution of dis
44、tinct invariants to the various failure criteria is considered insignificant 1-11. The model is expressed in the following forms: Tension fiber mode: 1 2 1 X t =Equation (6) Compression fiber mode: 1 2 1 X c =Equation (7) Tension matrix mode: 2 2 12 2 1 YS t + =Equation (8) Compression matrix mode:
45、2 2 12 2 1 YS c + =Equation (9)5 An example of interactive theories is the Tsai-Wu failure criterion, which has been implemented in CAE software such as ABAQUS. In this model, a single quadratic polynomial equation involving all stress components is used 1-12. The model is expressed in the following
46、 formsEquation (10) where F= 1 X - 1 X 1 tc , F= 1 Y - 1 Y 2 tc , F= 1 XX 11 tc , F= 1 YY 22 tc , F= 1 S 66 2 , F- 1 2 (F F) 12 11 22 1/2 In above equations, X t , X c , Y t , Y c , S refer to the tensile strength, compressive strength, and shear strength of the individual lamina in principal ply di
47、rection (1, 2, 3), as illustrated in Figure 1.3 Figure 1.3 Schematic of the different failure micromechanisms in a fiber composite. There exist some excellent reviews on the failure theories that are applicable to a composite lamina 1-13 - 1-17. One notable work is called the “Worldwide Failure Exer
48、cise”, initiated by Hinton, Soden and Kaddour 1-13. This comprehensive review compares nineteen failure theories and experimental data. In general, the failure theories at the lamina level (first ply failure FPF) seem to be well established and are available to composite designers. The determination of ultimate failure of a laminate (ULF) is much more complicated. There is no generally acceptable mechanism on what causes the ULF failure. The overall steps in predicting ultimate laminate failure may include the following 1-14. First, the analysis is conducted on a laminate to determine the
