Fracture of PMMA

An unstable crack is primarily driven by the elastic energy already stored in the specimen (and not so much by the energy introduced into the specimen by the continued deformation). A pertinent experiment was carried out by Stalder [30], who investigated the impact fracture of PMMA using an instrumented hammer nose and standard notched Charpy specimens with sprayed-on graphite strain gages. With this double-instrumentation technique... 

Berry adopted a slightly different approach to evaluate y, and also confirmed the validity of Equation (12.2) for the fracture of PMMA and polystyrene by measuring the tensile strength of small samples containing deliberately introduced cracks of known magnitude. 

The peeling force, for a pressure-sensitive tape, is expended (dissipated) in the elongation of the filaments.(1A local temperature rise is observed in peeling(i 3) it has been attributed to the plastic and elastic deformation that occurs when these filaments are drawn.(D A large, transient temperature rise has been observed in the fracture of PMMA and of polystyrene. See the review of the thermal effects on pp. 136-139 in Doll.d )... 

Fig. 5. Typical acoustic emission (AE) waves observed at different zones and during fracture of cyclic loading of PMMA. The amplitude is drawn on...

Many studies [40-43] have been performed on the fracture behaviour of PMMA as a function of temperature or cross-head speed. As an illustration, Fig. 30 shows the critical stress intensity factor, K c, in a log-log plot as a function of temperature for various crack speeds [40]. The temperature range is limited to + 80 °C in order to avoid ductile tearing. In the stable crack growth regime of interest here, whatever the crack speed, K c decreases with increasing temperature. 

So, it is quite clear that ft transition motions are involved in the fracture behaviour of PMMA. The continuous smooth decrease of K c with increasing... 

Figure 3. Fracture surface of PMMA impacted under compressive shear stress. Left Magnification X18.5, fracture direction from top to bottom. Right The same spot, magnification XSQ.

ESR spectrum observed after the simultaneous fracture of PTFE with MMA at 77 K was found to be the quartet-quintet which is undoubtedly attributed to the propagating radical of PMMA. No trace of the PTFE radical was mixed in the observed spectrum. It is believed from both experimental and theoretical reasons that no radical is produced by a mechanical destruction of any solid consisting of a low molecular organic compound 31). Thus, the radicals produced by this mechanical action originate from not MMA but the PTFE polymers, although both solids of MMA and PTFE were fractured amultaneously. Accordingly the polymerization of MMA, which was proved by ESR, had been initiated not by the MMA radical but... 

Analysis of the fracture toughness of PMMA and of the shape of a single craze at a... 

Figure 5. Stress intensity factor, a KInmx. b Strain-energy release rate, GImax. c Normalized initiation energy, Uinit, and normalized energy for propagation, Uprop- Uneat PMMA is the energy to fracture neat PMMA (2 L0) d Stress-whitened area of the fracture surface, Sw, used to determine the transitions in 2 L15.

Figure 3. Surface damage produced by a truncated 15 cone under a load of IN. Evidence of fibrilation is seen in PTFE along with extensive plastic flow. The surfaces of PMMA and polycarbonate PC show that significant brittle fracture occurs.

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