Description / Abstract:
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 more 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 desirable 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 producing
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 much 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, vibration, 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
integrating 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 use
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 plastics. The basic
material properties necessary to the design of a homogeneous
structure are Young's modulus (E), Poisson's ratio (n), and failure
strength (sf). These properties for common materials, such as steel
and aluminum, are readily available in materials handbooks and
online resources, making 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 at 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 various 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 fiber–epoxy composite, the
basic lamina properties vary dramatically 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
engineering [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 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 failure 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
composite materials and then presents some recent, innovated CAE
design examples of composite structures by engineers from major CAE
developers and automobile original equipment manufacturers (OEMs)
and suppliers.