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Strain gages and dynamic caustics were used in this experiment to measure the V-notch crack initiation toughness and propagation toughness of polymethyl methacrylate (PMMA) specimens. Furthermore, a method of pasting strain gages on V-notch PMMA specimens for three-point bending test was proposed. The specimens were divided into five groups according to the opening angle (ω), and each group corresponded to two pasting methods: acute-angle pasting method and obtuse-angle pasting method. The results of notch stress intensity factors (NSIFs) obtained by strain gage measurement were consistent with the results calculated using the dynamic caustics method. The concept of the dimensionless notch stress intensity factor (DNSIF) was introduced for a better analysis of the effect of opening angles on cracking. The experimental results revealed that the initiation of V-notch crack in the specimens were inhibited more when ω was larger than 90° than for small opening angles. Under this condition, the specimens displayed higher cracking initiation toughness. Furthermore, the time required for crack initiation was longer, and the cracking was instantaneous. An analysis of the vicinity of the V-notch crack tip showed that with the increase in ω, the stress component decreased, and the rate of decrease became higher. This also explains the phenomenon wherein the specimens transformed from being easy to crack to not being so as ω increased. The experimental results showed that the crack propagation velocity and propagation toughness were also affected by the opening angle of the V-notch crack.

V-notch crack toughness of PMMA by strain gages and its comparison with caustics results under impact loading