Properties of cryogenic insulants

Relation of damping and fatigue damage of unidirectional fibre composites

Mechanical relaxation of polymers at low temperatures

Low-temperature viscoelastic behavior of unidirectional carbon composites

At low temperatures many properties are rather independent of polymer structure. This is true for the static fracture strength σUT, but not for the fracture toughness KIc, which is directly correlated to σUT. The reason is that dynamic processes with adiabatic heating and plastification of the crack tips (arrest lines) are involved in the measurement of KIc and the energy of fracture γ. The amount of plastification therefore depends on properties at higher temperatures which are different for most polymers. Consequently the question arises whether or not adiabatic heating occurs in a similar manner for σ UT measured at high deformation rates. It has been found that polymers become more ductile if a certain deformation rate is exceeded. Thus, brittleness of polymers is not increased under impact loading.

Fracture Properties of Polymers and Composites at Cryogenic Temperatures

When an alternating mechanical or electric load is applied, loss factors are necessary for estimating the energy dissipation or heat generation. For AC-superconducting magnets or rotating machinery with LHe-cooling this might become a non-neglegible factor of cooling costs.

G. Hartwig

Papers

Correlation of Dielectric and Mechanical Damping at Low Temperatures