Burst hoop pressure

Figure 13.17. Burst hoop pressure versus temperature...

Figure 13.17 shows that both temperature increase and plasticizer concentration increase contribute to the reduced burst hoop pressure. 

Similarly, the total downward pressure on the semicircular portion of the cylindrical shell below the diametral plane XX is also 2prL. These two equal and opposite pressures act to burst the cylinder longitudinally at the plane XX. The resisting force comes from the hoop stress. Thus... 

The early attempts to devise a bronze breech -loading cannon were unsuccessful because the backward pressure of the gas ultimately blew out the breech-block or else the gas created sufficient pressure against the walls of the barrel to burst it. As forged-alloy steels were perfected, breech-loading became a more practical possibility at the same time steel hoops or outer tubes were shrunk onto the barrel to strengthen it, or, at a later date, wire was wound around the barrel at high tension(Ref 2,p 83)... 

Chiou and Bradley [81] conducted hydraulic burst and stress rupture tests on 1.28mm thick (58v/o 87/ 35/87° hoop filament wound) tubes made from E-glass fibre/Brunswick LRF-571 DGEBA epoxy resin. There were 6% voids in the laminate. A co-cured nitrile rubber liner was employed, partly to keep the inner surface dry and partly to ensure that pressure could still be maintained if the GRP cracked during the tests. The tests followed 6 months immersion in static simulated sea water (Aquarium Systems Instant Ocean, p = 1023 kgm, pH = 8.2). The tubes had a high (1.5%) moisture uptake, although some of this might have been free water in the voids, but saturation was not reached. 

A further variant is the testing of pipes by pressurizing, usually with water, and holding a constant pressure until the pipe bursts. The burst is usually a weeping leak. The pressure develops hoop stresses in the pipe, which can be calculated from a knowledge of the pressure and pipe dimensions. The type of curve that now emerges is as in Fig. 1.11. 

If a thermoplastic composite pipe is pressurized rmder laboratory conditions (with the pipe ends freely moving) the stress/strain in the two principal, axial (ej and hoop ( y), directions exhibit a behavior schematically illustrated in Figure 1. Three aspects of this response, namely (1) the initial stiffness of the pipe associated with the slopes and Sy (2) nonlinearity in the cr/e response and (3) the ultimate failure of the pipe corresponding to the burst pressure, are rationalized by means of micro- and macromechanical modelling. These types of modelling of the short term structural response are the initial steps in the overall design procedure. 

A hydraulic burst-strength tester such as the one shown in Figure 12-7 is employed. A pressure intensifier such as the one shown in Figure 12-8 can also be used. This latter device is relatively simple and only requires the use of shop air and water or other suitable fluid. The test is carried out by simply pressurizing the specimen and uniformly increasing the pressure until the failure occurs. ASTM D 1599 requires the time to failure for all specimens to be between 60 and 70 sec. The system must be bled thoroughly, to avoid entrapment or air bubbles, prior to commencing each test. The specimen is considered to have failed when it develops a leak, crack, or rupture. The hoop stress can be calculated as follows ... 

The specimen failure is marked by continuous loss of pressure, bursting, abnormal ballooning, and leakage. The hoop stress in the specimens is calculated by using the formula described in Section 12.4.1. 

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