Study On Dynamic Mechanical Properties Of Cement Morar

Split Hopkinson pressure bar experimental technique is one of important experimental ways for measureing material dynamic mechanical properties,but, doing dynamic experiment for brittle material in Hopkinson pressure bar device using routine experiment and date processing method,whose result will be mistaken or even incredible. Other question is small destruct strain need to increase rising time of loading wave to reach to stress equilibrium before destruction. So many measuring is brought forward to improve experiment accuracy in studying of Hopkinson pressure bar device experimental ways for brittle material.The paper studied mainly some question in dynamic properties measuring in split Hopkinson pressure bar striking for brittle material (cement mortar) with pulse shaping technique, main tasks were as follows:1. Nonlinear finite element of a large software ls - dyna as a solution, and femb as a processor, parameter optimization of pulse shaping was numerical simulated, and effect of pulse shaping technique for brittle specimens in SHPB experiment. Geometric and material parameters of pulse shaper were adjusted and researched on effect of dynamic behavior in measuring dynamic properties of cylindric cement mortar. The result provided incident,reflected and transmitted strain-time curve, and axial strain-time curve of specimens,and it provided systemic and fruitful date for brittle material in split Hopkinson pressure bar striking. It is found that axial strain-rate in different place of specimens is different even though the shaped incident stress pulse generates a nearly constant strain-rate in the reflected pulse in the SHPB test. It implies that the achievement of a nearly constant strain-rate in the reflected pulse in the SHPB test may not be equivalent to a nearly constant strain-rate in the SHPB specimen.2. Dynamic properties of cement mortar materials was investigated by a large-diameter ( 74 mm ) split Hopkinson pressure bar apparatus in this paper,which to research shaping effect of different shape specimens in different striking velocity and different size,material pulse shaper. Strain guage is pasted in incident and transmission bar to record incident,reflected and transmitted wave. And computed strain rate,stress and strain of specimens between incident bar and transmission bar by date processing Software to analyse the effect of specimens shape on strain rate-time curve,stress-strain curve of cement mortar material and the effect of strain rate on stress-strain curve of specimens. And strain guage is pasted in the different place of specimens to measure its axial and radial strain and to analyse even though the rising time of incident pulse has prolonged and wave vibrate has weaken, but specimens whether has reached constant strain rate,axial strain is whether equilibrium and radial strain is whether existing etc. It is found that achieving"constant strain rate"deformation by pulse shaper is very difficult in dynamic experiment of brittle materials. If"constant strain rate"is seeked strictly, which will result in that dynamic properties of experiment will be reduced largely and strain rate in the specimens may not reach transition strain rate. In addition, it is also found that even though eliminating inertia-induced radial confinement effect is measured by designing geometry dimension of specimens and pulse shaper is used to prolong the rise-time of the incident pulse to ensure deformation equilibrium in the specimens, but axial strain in different place of specimens is not equal and very large radial strain still exist. Therefore, non-ignorable effect for experiment accuracy is induced by inertia-induced radial confinement effect.