A R Boccaccini et al. / Composites Science and Technology 65(2005)325-333 克K Fig. I. SEM micrograph showing the typical microstructure of the mullite fibre reinforced mullite matrix composite investigated [26] clamped to a steel sample holder without a backing Subsequently, samples for 4-point flexure strength plate. The gun employed for this study was a single test measuring 75 mm in length, 32 mm in width and stage laboratory gas gun capable of firing spherical 2.65 mm in height were carefully cut from the impacted up to 400 m/s. A detailed description of the facility impression left by the ballistic impact was placed projectiles with diameters up to 13 mm at velocities tiles. The samples were cut in such a way that th used is given by McQuillan [29]and a schematic dia- the centre of the sample. At least five samples for each gram of the gas gun is shown in Fig. 2. The gun uses testing condition were considered. As-received and im- compressed nitrogen gas to fire the projectile and is pacted samples were tested on a universal testing ma operated by a bursting-diaphragm firing mechanism. chine using a 4-point flexure fixture with 30-mm inner The compressed gas is transferred from the cylinder and 60-mm outer spans. Each specimen was placed in to the gas reservoir (on one end of the barrel), which the fixture such that its impacted side was under tension is joined to a breech adaptor. A suitable diaphragm is and the point of impact was located in the centre of the placed between the barrel and the breech adaptor. inner spans. Tests were conducted at a speed of I mm/ The pressure in the reservoir causes the diaphragm min using a 100 kN load cell. On the basis of data ob- to rupture, shooting the projectile through the barrel. tained during the 4point bending tests, Youngs modu The velocity of the projectile is controlled by the lus was calculated using the following relation The macroscopic damage of the samples after E=o impacts was recorded using a digital camera(Olympus D-510) where Breech Bursting Taper tube Target device Muzzle Fig. 2. Schematic diagram showing the gas gun used for the ballistic impact tests [291clamped to a steel sample holder without a backing plate. The gun employed for this study was a single stage laboratory gas gun capable of firing spherical projectiles with diameters up to 13 mm at velocities up to 400 m/s. A detailed description of the facility used is given by McQuillan [29] and a schematic dia￾gram of the gas gun is shown in Fig. 2. The gun uses compressed nitrogen gas to fire the projectile and is operated by a bursting-diaphragm firing mechanism. The compressed gas is transferred from the cylinder to the gas reservoir (on one end of the barrel), which is joined to a breech adaptor. A suitable diaphragm is placed between the barrel and the breech adaptor. The pressure in the reservoir causes the diaphragm to rupture, shooting the projectile through the barrel. The velocity of the projectile is controlled by the pressure, which is required to burst the diaphragm. The macroscopic damage of the samples after impacts was recorded using a digital camera (Olympus D-510). Subsequently, samples for 4-point flexure strength test measuring 75 mm in length, 32 mm in width and 2.65 mm in height were carefully cut from the impacted tiles. The samples were cut in such a way that the impression left by the ballistic impact was placed in the centre of the sample. At least five samples for each testing condition were considered. As-received and im￾pacted samples were tested on a universal testing ma￾chine using a 4-point flexure fixture with 30-mm inner and 60-mm outer spans. Each specimen was placed in the fixture such that its impacted side was under tension and the point of impact was located in the centre of the inner spans. Tests were conducted at a speed of 1 mm/ min using a 100 kN load cell. On the basis of data ob￾tained during the 4-point bending tests, Young
s modu￾lus was calculated using the following relation: E ¼ Fl2 ol1 16Jyo ; where, To auxiliary gas reservoir Target Bursting diaphragm Breech Barrel Muzzle Timing device Taper tube Sabot containing projectile Fig. 2. Schematic diagram showing the gas gun used for the ballistic impact tests [29]. Fig. 1. SEM micrograph showing the typical microstructure of the mullite fibre reinforced mullite matrix composite investigated [26]. A.R. Boccaccini et al. / Composites Science and Technology 65 (2005) 325–333 327