Microcracking of cross-ply composites under static and fatigue loads. Ph.D. Thesis

Thesis/Dissertation · Sat Dec 31 04:00:00 EST 1994

OSTI ID:147176

Liu, S

Recently, a variational mechanics analysis approach has been used to determine the thermoelastic stress state in cracked, cross-ply laminates. The analysis included a calculation of the energy release rate due to the formation of a microcrack in the 90 deg plies. A wide variety of composite material systems and cross-ply layups of generic type (0{sub m}/90{sub n}) sub s were tested during static loading. The variational mechanics energy release rate analysis can be used to predict all features of the experimental results and to draw some new conclusions about the progression of damage in cross-ply laminates. The recommended experiments are to measure the density of microcracks as a function of applied stress. Such results can be fit with the energy release rate expression and used to measure the microcracking or intralaminar fracture toughness. Experiments that measure only the stress to initiate microcracking are specifically not recommended because they do not give an accurate measure of the microcracking fracture toughness. Static fatigue, thermal cycling, and combined thermal and mechanical fatigue experiments were run on several material systems and many cross-ply layups. A modified Paris-law was used and the data from all layups of a single material system were found to fall on a single master Paris-law plot. The authors claim that the master Paris-law plot gives a good characterization of a given material system`s resistance to microcrack formation during fatigue loading.

• Research Organization: Utah Univ., Salt Lake City, UT (United States)
• OSTI ID: 147176
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
COMPOSITE MATERIALS
FRACTURE PROPERTIES
LAYERS
REINFORCED MATERIALS
STATIC LOADS
STRESS ANALYSIS
THERMOELASTICITY