13th International Conference on Fracture June 16–21, 2013, Beijing, China -3- Figure 1. One-Point Bend apparatus 2.2. Material Tests were carried out using SENB geometries. Due to inherent manufacturing constraints advanced ceramic materials have limitations on available specimen dimensions. Initial testing was carried out on PMMA with specimen span of 18 mm, height of 6 mm and thickness of 3 mm. Testing on the ceramic material was carried out on specimens with a span of 28.5 mm, height 6.25 mm and thickness of 4.76 mm. Future testing will involve specimens whose dimensions are further restricted with a span of 14 mm, height of 5 mm and thickness of 2 mm. The PMMA specimens were notched at 45-degree angle to a depth of 1 mm. Pre-cracks were subsequently introduced using a razor blade. Tests were preformed only on specimens whose pre crack was straight. For brittle materials like ceramics pre cracking is not an option and so samples had a notch root radius of 150 µm for all grades with a notch depth of 1.5 mm. Table 1. shows static fracture toughness values for PMMA and ceramic A and B. The PMMA tests were carried out using the standard three-point bend method, [11]. Static fracture results for the advanced ceramics A and B were taken from a previous study, [12] using a three-blunt notch analytical approach. Table 1. Static Fracture toughness values Material K1c(MPa√m) PMMA 1.61 Ceramic A 7.70 Ceramic B 2.80 3. Fracture Toughness determination 3.1. Data Reduction The load applied to the specimen is given below and is based on one-dimensional wave theory, [10]: P(t) =EA0[ εI (t)+ εR(t)], (1) where E and Ao are the Young’s modulus and cross-sectional area of the bar respectively. The particle velocity at the end of the incident bar is given by: v=C0[ εI (t)− εR(t)], (2) where C0 is the longitudinal wave velocity of the pressure bar. Integration of the velocity will also yield displacement at the end of the bar. It is important to note that specimens must be sufficiently brittle so to fully fracture before they loose contact with the incident bar. Once the specimen leaves the end of the bar a free end boundary condition prevails and the above equations are no longer applicable. Up to this time Eq. (1) can be
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