Buckling of thermoviscoelastic structures under temporal and spatial temperature variation
The problem of lateral instability of a viscoelastic in-plane loaded structure is considered in terms of thermorheologically simple materials. As an example of a generally in-plane loaded structure, we examine the simple column under axial load: Both cyclic loading is considered (with constant or in...
| Summary: | The problem of lateral instability of a viscoelastic in-plane loaded structure is considered in terms of thermorheologically simple materials. As an example of a generally in-plane loaded structure, we examine the simple column under axial load: Both cyclic loading is considered (with constant or in-phase variable temperature excursions) as well as the case of constant load in the presence of thermal gradients through the thickness of the structure.
The latter case involves a continuous movement of the neutral axis from the center to the colder side and then back to the center.
In both cases, one finds that temperature has a very strong effect on the rate at which instabilities evolve, and under in-phase thermal cycling the critical loads are reduced compared to those at constant (elevated) temperatures. The primary effect of thermal gradients beyond that of thermally-induced rate accelerations is a rate increase occasioned by the generation of an "initial imperfection" or "structural bowing." This latter effect, which is proportional to both the temperature gradient and the coefficient of thermal expansion (presumed homogeneous in this study), can in fact be dominant. Because the coefficient of thermal expansion tends to be large for many polymeric materials, it may be necessary to take special care in lay-up design of composite structures intended for use under compressive loads in high-temperature applications. Finally, the implications for the temperature
sensitivities of composites to micro-instability (fiber crimping) are also apparent from the results delineated here.
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