M.G. Holmquist et al./Composites: Part A 34(2003)163-170 the specimen inlet occurred and was associated with an audible sound. This was interpreted as the onset of damage A hysteresis could then be observed during unloading. For all specimens, the failure initiated along the line formed by Final fracture he edge of the outer ply as shown on the lacquer-coated specimen in Fig. 4. Delamination of the wound fibre cloth was the main failure mode. The tube could be pressurised Progress of again, although fow rates increased relative to the first two cycles for a given applied pressure, suggesting the presence of larger flow short-circuits through the composite wall. The -o- Cycle 5 tube still held pressures above that of the previous maximum, indicating that some mechanical integrity was still retained. The crack front on the specimen surface Flow(W/s) gradually propagated towards the ends of the tube causing new pressure drops(cycle 4 in Fig. 3). At still higher Fig. 3. Internal absolute pressure in the tube versus flow rate through the tube surface. The tube failed by delamination(end of cycle 3 pressures(about 4.5 MPa), the crack front on oated specimen was observed to deviate at an angle, measurements on other porous ceramics [39]. A typical breaking fibres parallel to the tube axis in a combination of curve of flow rate as a function of pressure is shown in Fig 3. shear and tensile loading (location 2 in Fig. 4). The new In the first two cycles, the pressure was increased and crack trajectory possibly resulted from the constraint on the released without any sign of hysteresis. Upon the third cycle deformation imposed by the glued ends of the tubes. The at a maximum pressure of 3.5 MPa, a pressure drop at test was terminated when the pressure could no longer be increased and the gas tank was emptying too rapidly. In some cases, possibly depending on the rate of the pressur increase, the pressure caused the tube to blow apart as shown in Fig. 5. Cross-sections of tested tubes confirmed that delamina- tion was the major mode of failure, the crack propagating inwards with a spiral trajectory between the cloth layers (Fig. 6). Upon completion of the test, the crack propagated beyond the location of the inner termination of the wrap, making the tube wall only one layer thick. Another delamination crack was observed at the termination of 2 Fig 4. The tubes glued with epoxy resin to brass fixtures. The brass xtures were connected to each other by a central rod, running inside the tube. Failure sequence of the tubes were: (1)delamination starting at the ermination of the wound prepreg followed by (2) deviation of the crack front resulting in failure of fibres parallel to tube axis. Fig. 5. Tube blown up frommeasurements on other porous ceramics [39]. A typical curve of flow rate as a function of pressure is shown in Fig. 3. In the first two cycles, the pressure was increased and released without any sign of hysteresis. Upon the third cycle at a maximum pressure of 3.5 MPa, a pressure drop at the specimen inlet occurred and was associated with an audible sound. This was interpreted as the onset of damage. A hysteresis could then be observed during unloading. For all specimens, the failure initiated along the line formed by the edge of the outer ply as shown on the lacquer-coated specimen in Fig. 4. Delamination of the wound fibre cloth was the main failure mode. The tube could be pressurised again, although flow rates increased relative to the first two cycles for a given applied pressure, suggesting the presence of larger flow short-circuits through the composite wall. The tube still held pressures above that of the previous maximum, indicating that some mechanical integrity was still retained. The crack front on the specimen surface gradually propagated towards the ends of the tube causing new pressure drops (cycle 4 in Fig. 3). At still higher pressures (about 4.5 MPa), the crack front on the lacquer￾coated specimen was observed to deviate at an angle, breaking fibres parallel to the tube axis in a combination of shear and tensile loading (location 2 in Fig. 4). The new crack trajectory possibly resulted from the constraint on the deformation imposed by the glued ends of the tubes. The test was terminated when the pressure could no longer be increased and the gas tank was emptying too rapidly. In some cases, possibly depending on the rate of the pressure increase, the pressure caused the tube to blow apart as shown in Fig. 5. Cross-sections of tested tubes confirmed that delamina￾tion was the major mode of failure, the crack propagating inwards with a spiral trajectory between the cloth layers (Fig. 6). Upon completion of the test, the crack propagated beyond the location of the inner termination of the wrap, making the tube wall only one layer thick. Another delamination crack was observed at the termination of Fig. 5. Tube blown up from escaping gas. Fig. 3. Internal absolute pressure in the tube versus flow rate through the tube surface. The tube failed by delamination (end of cycle 3). Fig. 4. The tubes were glued with epoxy resin to brass fixtures. The brass fixtures were connected to each other by a central rod, running inside the tube. Failure sequence of the tubes were: (1) delamination starting at the termination of the wound prepreg followed by (2) deviation of the crack front resulting in failure of fibres parallel to tube axis. M.G. Holmquist et al. / Composites: Part A 34 (2003) 163–170 167