The response of structures and materials subject to impulsive loads remains a field of intense research. The dynamic loading and temperature increase affect the material's mechanical/failure response. For example, strains due to explosive blast will increase at rates from 102 to 104 s-1, leading to regimes of elastic/plastic wave propagation, plane stress and adiabatic deformations. Few constitutive models consider high strain rate effects, however some constitutive approaches that were developed and tested at low strain rate regimes will also be addressed here due to their relevance. Specific reference will be made to strain rate regimes close to 104 s-1, where shock waves may develop. The paper focuses on constitutive models for polycrystalline face-centred-cubic (FCC) metals since their behaviour under high strain rate regimes is not yet fully understood mostly due to path loading dependency. Reference is also made to aluminium alloys since they are widely used in virtually all fields of industry and in armour and protective structures and systems. A basic review of the main theoretical aspects that constitute the basis for most of the constitutive models described is also presented and the main features of each model are thoroughly discussed.

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Direct impact Hopkinson pressure bar systems offer many potential advantages over split Hopkinson pressure bars, including access to higher strain rates, higher strains for equivalent striker velocity and system length, lower dispersion, and faster achievement of force equilibrium. Currently, these advantages are gained at the expense of all information about the striker impacted specimen face, preventing the experimental determination of force equilibrium, and requiring approximations to be made on the sample deformation history. In this paper, we discuss an experimental method and complementary data analysis for using photon Doppler velocimetry to measure surface velocities of the striker and output bars in a direct impact bar experiment, allowing similar data to be recorded as in a split bar system. We discuss extracting velocity and force measurements, and the precision of measurements. Results obtained using the technique are compared to equivalent split bar tests, showing improved stress measurements for the lowest and highest strains in fully dense metals, and improvement for all strains in slow and non-equilibrating materials.

In uni-axial compression at strain rates above 10 4 s −1 , FCC metals exhibit a rapid increase in strength. Mechanisms proposed to be responsible for this transition can be broadly split into two categories; that mobile dislocation velocities become limited by quasi-viscous scattering from phonons, or that some change occurs in the evolution of the materials dislocation structure. The relative contribution of each mechanism is difficult to identify, in part due to a scarcity of experimental measurements in varying deformation conditions. In this paper, we perform uni-axial compression experiments that reach rates between 10 4 and 10 5 s −1 , at temperatures between 300 and 600K. Analysis of the data at 0.1 strain shows both the absolute and relative levels of thermal softening increase with strain rate, an anomalous result in comparison to both existing models and measurements below the transition.

Cobalt Chrome is used extensively within the biomedical industry for hip, knee and shoulder prostheses. These components are manufactured using a range of different processes which includes machining. In order to develop Finite Element Models of machining processes, it is necessary to develop the constitutive model of the workpiece material at high strain rates over different temperatures. During this research, Split Hopkinson Pressure Bar tests were conducted over a wide processing domain of temperatures (298-873 K) and strain-rates (600-1400s-1) to predict the constitutive model of biomedical grade Cobalt Chrome based on modified Zerilli-Armstrong, modified Johnson-Cook and strain compensated Arrhenius-type models. The prediction capability of these models was evaluated in terms of average absolute relative error and correlation coefficient between predicted and experimental flow stress values. Results demonstrated that the modified Zerilli-Armstrong model can track the deformational behaviour more accurately throughout the entire processing domain investigated compared to the other models. The model recorded an average absolute relative error of 2.71% and a correlational coefficient of 0.98.