Page 35 - Using ANSYS for Finite Element Analysis Dynamic, Probabilistic, Design and Heat Transfer Analysis

22 • using ansys for finite eLement anaLysis
fabricates the materials into a finished structure can do almost nothing
to change those “in-built” properties. However, a composite material is
formed at the same time, as the structure is itself being fabricated. This
means that the person who is making the structure is creating the prop-
erties of the resultant composite material, and so the manufacturing pro-
cesses they use have an unusually critical part to play in determining the
performance of the resultant structure.

2.1.1.1 Loading

There are four main direct loads that any material in a structure has to
withstand: tension, compression, shear, and flexure.

Tension: Figure 2.2 shows a tensile load applied to a composite. The
response of a composite to tensile loads is very dependent on the
tensile stiffness and strength properties of the reinforcement fibers,
since these are far higher than the resin system on its own.
Compression: Figure 2.3 shows a composite under a compressive
load. Here, the adhesive and stiffness properties of the resin system
are crucial, as it is the role of the resin to maintain the fibers as
straight columns and to prevent them from buckling.
Shear: Figure 2.4 shows a composite experiencing a shear load. This
load is trying to slide adjacent layers of fibers over each other.
Under shear loads the resin plays the major role, transferring
the stresses across the composite. For the composite to perform
well under shear loads the resin element must not only exhibit
good mechanical properties but must also have high adhesion to
the reinforcement fiber. The interlaminar shear strength (ILSS) of

Figure 2.2. Illustrates the tensile load applied to a composite body.

Figure 2.3. Illustrates the compression load applied to a composite body.