The effects of stress ratio and load sequence on damage accumulation in quasi-isotropic laminates

Book · Sun Dec 31 04:00:00 EST 1995

OSTI ID:237727

Bartley-Cho, J D; Lee, S; Hahn, H T ^[1]

---

1. Univ. of California, Los Angeles, CA (United States). Mechanical and Aerospace Dept.

The effects of load sequence and stress ratio on damage development were studied for a quasi-isotropic laminates under high cycle fatigue conditions. Ply crack density was used as the main damage parameter. AS4/3501-6 quasi-isotropic laminates of [0/{+-}45/90]{sub S3} lay-up were fatigued in tension-tension to 10{sup 6} cycles. Constant amplitude tests at a stress ratio, R=0.1, and frequency of 10 Hz were performed to gain baseline crack density data. Additional constant amplitude tests at 60% of ultimate tensile strength and at R=0.4, 0.6, and 0.8 were performed. Two-stress-level two block tests were performed in high/low and low/high sequences at 40%/30% and 40%/20% of ultimate tensile strength. The R variation tests showed that, for outer plies, damage mode changed from ply cracking to delamination as R decreased. The two block spectrum tests revealed that low/high fatigue resulted in a higher crack density than for high/low fatigue. A cumulative damage method was developed based on crack density data and the assumption that damage state reached is independent of load history. The method predicted unconservatively, either giving values between or above the observed crack densities.

• OSTI ID: 237727
• Report Number(s): CONF-9510177--; ISBN 1-56676-376-2
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
CARBON FIBERS
COMPOSITE MATERIALS
CRACKS
EPOXIDES
EXPERIMENTAL DATA
FATIGUE
INTERFACES
LAYERS
SAMPLE PREPARATION
STRESSES
ULTIMATE STRENGTH