A three-phase cylinder model for residual and transformational stresses in SMA composites

Conference · Sat Dec 31 04:00:00 EST 1994

OSTI ID:395153

Berman, J B; White, S R ^[1]

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1. Univ. of Illinois, Urbana, IL (United States). Dept. of Aeronautical and Astronautical Engineering

SMA composites are a class of smart materials in which shape memory alloy (SMA) actuators are embedded in a polymer matrix composite. The difference in thermal expansion between the SMA and the host material leads to residual stresses during processing. Similarly, the SMA transformations from martensite to austenite, or the reverse, also generate stresses. These stresses acting in combination can lead to SMA/epoxy interfacial debonding. In this study the residual and transformational stresses are investigated for an SMA wire embedded in a graphite/epoxy composite. A three phase micromechanical model is developed. The SMA wire is assumed to behave as a thermoelastic material. Nitinol{trademark} SMA austenitic and martensitic transformations are modeled using linear piecewise interpolation of the experimental data. The interphase is modeled as a thermoelastic polymer. A transversely isotropic thermoelastic composite is used for the outer phase. Stress-free conditions are assumed immediately before cool down from the cure temperature. The effect of SMA and coating properties on residual and transformational stresses are evaluated. A decrease in stresses at the composite/coating interface is predicted through the use of thick, compliant coatings. Reducing the recovery strain and moving the transformation to higher temperatures are also effective in reducing residual stresses.

• OSTI ID: 395153
• Report Number(s): CONF-940691--; ISBN 1-56676-171-9
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
COMPOSITE MATERIALS
CRYSTAL-PHASE TRANSFORMATIONS
EPOXIDES
FABRICATION
FAILURES
INTERFACES
MATHEMATICAL MODELS
NICKEL ALLOYS
SHAPE MEMORY EFFECT
STRESSES
TIN ALLOYS