BEHAVIOUR OF FIBROUS-FE RROCEMENT UNDER IMPACT AND BLAST LOADING

Abstract

The resistance of composite materials to suddenly applied loads, such as impact and blast, are gaining importance because of their vast potential in civil and military applications. Previous investigations reveal the enhancement in energy absorbing capacity of ferrocement by the inclusion -of discrete fibres in the matrix, and therefore, fibrous-ferrocement is expected to have high resis-tance to such loads. This study was based on an experitnental investigation using ferrocement control specimens, reinforced with 1.2 and 3 layers of square woven wire mesh, having corresponding sections 20, 30 and 40 mm thick. For fibrous--ferrocement specimens, with similar mesh layers and thicknesses, steel hooked fibres were included in the cement mortar matrix at a constant volume fraction of 0.5%. For each type 3 to 4 companion specimens were tested and studied. Impact resistance was studied on 1m x 1m slabs, imparted with drop impact loading using a specially designed and fabricated 'Impact Test Set-up'. Blast loading was provided internally to hollow, cylindrical specimens, closed at one end and having similar mesh layers, fibre reinforcement and section thick-nesses as the slabs. A fabricated 'Blast Test Set-up' was used to provide the explosive force using ' weighed quantities of plastic explosive. In both impact and blast studies, in addition to a qualitative study, a quantitative assessment was conducted by measuring leakage rate of water at a constant head, through the damaged area. using specially designed °Leakage Test Set-ups' . respectively. From the recorded results, plots of impact energy versus leakage rate for the six variations in volume fraction of - reinforcement, including three with steel fibres, in slabs, and in the case of cylinders, volume fraction versus leakage rate, for a constant quantity 'of explosive charge, have been drawn. Least square regression equations are presented in each case. An attempt has (iv) been made to correlate the effect of the a oio :iv charge with a corresponding drop impact energy. Limited tests were also conducted on the effect of mechanical compaction and the repairability of damaged slabs. An increased -impact and blast resistance of fibrous-ferrocement has been observed, both qualitatively and quarntltaLiveiy, vx -a-vJrs fe rrocernent. Apart from a superior cracking behaviour and crack arrest mechanism, fibrous-ferroce- rent offered a greater absorption of impact energy till first crack by 275%, 88.6% and 61.54% for the respective types of specimens with 1, 2 and 3 mesh layers , over their ferrocerrietit - parallels. For approximately the same range of damage degree, as suggested by the leakage rates, the tang of camulat.,.ve ir,fpact energy impartedl to ferrocement specimens was 2436.44 to $599.2 kg cm,. whilee it was &091.1 to 14618.64 kg cm for those of fibrous-ferrocement. The damage inflicted by the explosive, as recorded by the leakage rates, were reduced by 62.25% and 81.31% in the fibrous-ferrocement specimens with 2 and 3 mesh layers respectively, when compared with the corresponding ferrocernent ones. Over and above the imprgvemenf in blast resistance, the role of the fibres in imparting shatter proofness to the material was clearly obs