Cyclic mechanical deformation

The knowledge of the total fracture energy of concrete determined by equilibrium tests is especially important for structures operating in corrosive environments, shock, and cyclic mechanical loads because in this case the material acts, as a rule, beyond ultimate strength (descending branch of the deformation graph, Figure 3.11). 

Shape-memory properties can be quantified in cyclic, stimuli-specific mechanical tests [23,40]. Each cycle consists of the SMPC and the recovery of the original, permanent shape. From the data obtained, the shape fixity ratio (Rf) and the shape recovery ratio (/ r) can be determined (see, e.g., [40-42] and Chapter Characterization Methods for Shape-Memory Polymers in this volume). Rf describes the ability of the switching segment to fix a mechanical deformation, e.g., an elongation to applied during SMCP resulting in the temporary shape. Rr quantifies the ability of the material to memorize its permanent shape. Different test protocols have been developed. They differ in SMCP, which can be performed under constant strain or constant stress conditions (see Chapter Characterization Methods for Shape-Memory Polymers in this volume). The recovery process under stress-free condition enables the determination of the switching temperature Tsw for thermally-induced SMP. 

The extent to which a deformation can be fixed as temporary shape and the recoverability of the permanent shape are the most important properties determined for quantifying the SME on the macroscopic level. These properties depend on parameters of the SMCP, such as thermal conditions, kinetics, and type of mechanical deformation. Cyclic, thermomechanical experiments are performed to obtain a full description of parameters, which quantify the shape-memory properties. 

When a comparison is made between the two plots, it is revealed that the upper sensor curves appear to be noisier and more hysterical as compared to the lower sensor curves. This signifies an important difference in energy absorption/release mechanism and mechanical deformation phenomena (compression and traction) at the top and bottom faces of the composite specimen during cyclic loading. 

CF is the interaction of irreversible cyclic plasfic deformation with localized corrosion activity. The combination of each of fhe mechanism, and fhe fransition from initiation to propagation is a matter under present research and of considerable technological importance. Corrosion pits have been routinely observed to nucleate crack growth in structures... 

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