Dynamic constitutive relation of EMC over a broad range of temperatures and strain rates
In this paper, dynamic properties of EMC were studied sat different temperatures and different strain rates. Firstly EMC was investigated by quasi-static tests. Secondly a series of dynamic compressive experiments of EMC were conducted using the Split Hopkinson Pressure Bar (SHPB) at high strain rates. Corresponding measurements were conducted at temperatures ranging from 20°C to 200°C. The results indicate that the yield strength and flow stress of EMC increase remarkably with the increase of strain rate. However, the yield strength of EMC is almost unchanged with the increase of temperature which is ranging from 20°C to 200°C.
Some experiments with the split hopkinson pressure bar
Abstract A n application of the split Hopkinson pressure bar to the dynamic testing of materials is given whereby continuous records of the strain vs. time, strain rate vs. time, stress vs. time, and stress vs. strain may be simultaneously recorded. For many materials a nearly constant true plastic strain rate can be maintained for loading durations on the order of 100 μsec. The assumptions made in applying the method are checked experimentally. Three annealed face centred cubic metals—lead, aluminium, and copper, are tested both dynamically and at lower strain rates to determine their rate sensitivity. The results indicate that a single thermally activated mechanism is predominant. A possible mechanism of this type is the intersection of glide and forest dislocations. In aluminium, the previous strain rate history of loading is shown to affect the material's dynamic response only. A rapid annealing effect is also evidenced. Finally, the method is shown to be applicable to some non-metallic materials.
Mechanical behaviour and durability of high volume fly ash cementitious composites
The purpose of this research is to separate different morphological particles of ASTM class F fly ash, and study their effect on mechanical behaviour and durability of high volume cementitious mixtures. In this research wet separation of raw fly ash is carried out, which resulted in three layers of different morphological particles. The first layer of particles float, comprise of about 1-5% of fly ash, is identified as cenospheres or hollow spheres. The second layer of particles is measured to be 55-60% of raw fly ash and consisting of porous spherical and rounded particles rich in Si and Al. The third layer particles is measured to be about 35-40% of raw fly ash. High volume fly ash cementitious composites containing second or third layer particles are tested under compression and bending, highlighting a higher strength and ductility in comparison to cementitious ones containing raw fly ash particles. KEYWORDS. Cementitious matrix; Raw fly ash; Second layer particles; Third layer particles.