Nanoscale variation in energy dissipation in austenitic shape memory alloys in ultimate loading cycles

Wavy behaviours of hysteresis energy variation in nanoscale bulk of thermomechanical austenitic NiTi shape memory alloy are reported in ultimate nanoindentation loading cycles. One sharp and two spherical tips were used while two loading-unloading rates were applied. For comparison, another austenitic copper-based shape memory alloy, CuAlNi shape memory alloy, and a metal with no phase transition, elastoplastic Cu, were investigated. In shape memory alloys, the hysteresis energy variation ultimately undergoes a linear decrease with internal wavy fluctuations and no stabilisation was observed. The internal energy fluctuation in these alloys was found dissimilar depending on the loading-unloading rate and the indentation tip geometry. In contrast, there was an absence of both overall and internal variations in hysteresis energy for Cu after the second loading cycle. The underlying physics of these variations is discussed and found to be attributed to both the created dislocations and ratcheting thermal-mechanical behaviour of the phase-transformed volume in shape memory alloys.

Strain rate effects for strength of geopolymer concrete

The effects of strain rate on compressive and tensile strength of fly ash based geopolymer concrete were investigated experimentally. Four mixes of geopolymer concrete using different alkaline solutions and under vary curing conditions were prepared. One mix of ordinary Portland cement (OPC) concrete was prepared for comparison. Both Quasi-Static tests using standard MTS and dynamic tests using Split-Hopkinson pressures bar (SHPB) were conducted, which were giving varying strain rate loadings from 10‾⁷ to 103 per second. The strain rate effect is presented as the ratio of dynamic compressive strength to static compressive strength (DIF). Results show that DIFs of geopolymer concrete are generally higher than those of OPC concrete at strain range of 187/s to 346/s (compression tests) and 7/s to 13/s (splitting tensile tests), respectively. This tendency is independent on loading regimes (compression or tension). This suggests that geopolymer concrete can be used as an alternative construction material to OPC concrete for the structures which has a high risk of being subjected to impact loadings.

Strain rate effect of high purity aluminum single crystals: experiments and simulations

In order to study the strain rate effect on single crystal of aluminum (99.999% purity), aluminum single crystals are fabricated and subjected to uniaxial compression loading at quasi-static and dynamic strain rates, i.e., from 10-4 s-1 to 1000 s-1. The orientation dependence is also investigated with single slip or multi slip. The stress-strain curves of pure Al single crystals along two orientations and at different strain rates are obtained after measuring initial orientation using the Laue Back-Reflection technique. Crystal Plasticity Finite Element Method (CPFEM) with three different single crystal plasticity constitutive models is used to simulate the deformations along two orientations under various strain-rates. The classical and two newly developed single crystal plasticity models are used in the investigation. The simulation results of these models are compared to experimental results in order to study their abilities to predict finite plastic deformation of single crystalline metal over a wide strain rate range.

Optimising technical skills and physical loading in small-sided basketball games

Differences in physiological, physical, and technical demands of small-sided basketball games related to the number of players, court size, and work-to-rest ratios are not well characterised. A controlled trial was conducted to compare the influence of number of players (2v2/4v4), court size (half/full court) and work-to-rest ratios (4x2.5 min/2x5 min) on the demands of small-sided games. Sixteen elite male and female junior players (aged 15-19 years) completed eight variations of a small-sided game in randomised order over a six-week period. Heart rate responses and rating of perceived exertion (RPE) were measured to assess the physiological load. Movement patterns and technical elements were assessed by video analysis. There were ∼60% more technical elements in 2v2 and ∼20% more in half court games. Heart rate (86 ± 4% & 83 ± 5% of maximum; mean ± SD) and RPE (8 ± 2 & 6 ± 2; scale 1-10) were moderately higher in 2v2 than 4v4 small-sided games, respectively. The 2v2 format elicited substantially more sprints (36 ±12%; mean ±90% confidence limits) and high intensity shuffling (75 ±17%) than 4v4. Full court games required substantially more jogging (9 ±6%) compared to half court games. Fewer players in small-sided basketball games substantially increases the technical, physiological and physical demands.