ABSTRACT No standardised device is available yet to measure contact forces continuously during tr... more ABSTRACT No standardised device is available yet to measure contact forces continuously during transverse impacts caused by a projectile on a metal plate or a thin-walled structure. This study describes the design and validation phases of an instrumented projectile (mass = 1 kg) that can be used to achieve such measurements. The impact force, indeed, is computed from the strain data collected by some strain gauges glued on to a projectile part, which remains elastic during shock. Under numerically defined conditions, the projectile geometry makes it possible to record signals that are not disturbed by the reflections of the compressive and tensile strength waves appearing inside the projectile during and after shock. Gauge signal post-filtering is then virtually useless. The strain gauge-instrumented projectile sensitivity is used to study the effects of small clamping pressure variations during the transverse impact study on shipbuilding steel plates. A second application deals with the impact of an automotive steel dome initially drawn with a bulge test apparatus.
It is known that deformation via martensitic transformation stabilises the martensite in NiTi sha... more It is known that deformation via martensitic transformation stabilises the martensite in NiTi shape-memory alloys, as manifested in the increase of the temperature for the reverse transformation of the deformed martensite. This stabilisation has direct implication to the design of shape-memory devices. This study investigates the effect of annealing temperature after cold working on the martensite stabilisation effect of a
ABSTRACT This paper reports the tensile deformation behaviour of near-equiatomic NiTi plates with... more ABSTRACT This paper reports the tensile deformation behaviour of near-equiatomic NiTi plates with circular, elliptical and square holes. The investigation is done both experimentally and by mathematical modelling. It is found that the nominal stress-strain curve of such structures deviates from typical stress-strain variation of NiTi with flat stress plateaus, by exhibiting stress gradients over the forward and reverse transformations of the hole-affected areas. The hole-affected length is nearly triple the lateral dimension of the hole, and when 33% of the gauge length is covered by (circular) holes, the entire sample behaves like a functionally graded material. Such mechanical behaviour is advantageous for achieving better load-displacement controllability and wider stress window for shape memory actuation and sensing.
ABSTRACT No standardised device is available yet to measure contact forces continuously during tr... more ABSTRACT No standardised device is available yet to measure contact forces continuously during transverse impacts caused by a projectile on a metal plate or a thin-walled structure. This study describes the design and validation phases of an instrumented projectile (mass = 1 kg) that can be used to achieve such measurements. The impact force, indeed, is computed from the strain data collected by some strain gauges glued on to a projectile part, which remains elastic during shock. Under numerically defined conditions, the projectile geometry makes it possible to record signals that are not disturbed by the reflections of the compressive and tensile strength waves appearing inside the projectile during and after shock. Gauge signal post-filtering is then virtually useless. The strain gauge-instrumented projectile sensitivity is used to study the effects of small clamping pressure variations during the transverse impact study on shipbuilding steel plates. A second application deals with the impact of an automotive steel dome initially drawn with a bulge test apparatus.
It is known that deformation via martensitic transformation stabilises the martensite in NiTi sha... more It is known that deformation via martensitic transformation stabilises the martensite in NiTi shape-memory alloys, as manifested in the increase of the temperature for the reverse transformation of the deformed martensite. This stabilisation has direct implication to the design of shape-memory devices. This study investigates the effect of annealing temperature after cold working on the martensite stabilisation effect of a
ABSTRACT This paper reports the tensile deformation behaviour of near-equiatomic NiTi plates with... more ABSTRACT This paper reports the tensile deformation behaviour of near-equiatomic NiTi plates with circular, elliptical and square holes. The investigation is done both experimentally and by mathematical modelling. It is found that the nominal stress-strain curve of such structures deviates from typical stress-strain variation of NiTi with flat stress plateaus, by exhibiting stress gradients over the forward and reverse transformations of the hole-affected areas. The hole-affected length is nearly triple the lateral dimension of the hole, and when 33% of the gauge length is covered by (circular) holes, the entire sample behaves like a functionally graded material. Such mechanical behaviour is advantageous for achieving better load-displacement controllability and wider stress window for shape memory actuation and sensing.
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Papers by Gérard Rio