Composite Materials Research Progress

Damage Evaluation and Residual Strength Prediction of CFRP Laminates … 173
the function f(x) is used to estimate the overall material damage when composite laminate are
subjected to an out-of-plane load. Because of its synthesis capability the function f(x) can be
used to summarize the whole material damage history and in the case of the transversal load
tests the integral of the function f(x), Int(f), over the domain ΩAE was calculated:
Int
⎛ Es
⎞
f = ∫ Ln⎜ ⎟dΩ
(6)
⎝ Ea
⎠
( )
Ω
AE
The values of Int(f) are influenced by the complete trend of f(x) and by the extension of
the AE domain.
Applications
Case study 1: materials and method
The composite laminates used for the tensile tests were different in terms of lay-up
(unidirectional laminates (UD), angle-ply laminates (AP) and quasi-isotropic laminates (QI),
fibre volume percentage and laminates thickness.
The pre-pregs were made by T-300 graphite fibres and epoxy matrix. Specimens were
cured in autoclave then cut by a diamond saw.
The characteristics of these three types of laminates are reported in Table 1. For each type
ten specimens were tested.
Table 1. Types of laminates used for the tensile tests
Laminate type ID Lay-up
Fibre
Volume
(%)
Thickness
(mm)
Unidirectional UD [0°]8 60 1.4
Angle ply AP [±45°]4S 30 2.8
Quasi isotropic
QI1 [0°,90°, ±45°]4S 60 1.4
QI2 [0°, ±45°, 90°]4S 60 1.4
QI3 [0°,90°, ±45°]4S 30 2.8
Specimen dimensions were 250 mm in length and 25 mm in width for all types of
laminates as recommended by ASTM 3039M for AP and QI lay-ups and the gage length was
140 mm, as shown in figure 4A.
Uniaxial tensile tests were done under displacement control using an INSTRON 8032
with a 100 kN load-cell, and speed of 0.05 mm/sec.
In order to reduce the acquisition of spurious acoustic external signals [47] two noise
gates were assembled in a series configuration with the specimens as shown in figure 4B.