Brittle Rupture of Glass Plates
Guirguis Rezk SID 199991603 Objectives:
To understand mechanisms of the fracture of brittle materials (in this case, glass) To recognize the variations in deformation and failure mechanisms which occur with a difference in flaw size, (i.e. between scratched and unscratched samples) Defining flaw sizes in glass plates by employing linear elastic fracture mechanics (LEFM) Utilizing the Weibull statistics approach in predicting probable failure in brittle materials.
1. The thickness (t) and width (w) of the rectangular glass sample is measured. The first glass slide is placed in the Instron 3-point bending apparatus with the support span set at 60mm (See Figure 1 –picture for illustrative purposes only) Support Span 60mm Figure 1: Instron 3-point bending apparatus Downward Motion – Application of load
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The loading beam (Silicon Carbide) is lowered at 10mm per second onto the plate. The load is applied until the glass breaks against the two supports (also of Silicon Carbide). The values for maximum load and deflection are recorded from the apparatus. Steps 1-4 are repeated for ten different samples. With a piece of emery paper scratch the surface of the glass slides along the width in the centre on one side only of a glass sample (see Figure 2)
4. 5. 6.
w Scratches Figure 2: Glass plate dimensions and orientation of scratches
Steps 1-6 are repeated for 10 samples ensuring that the scratched surface is placed face down in the testing apparatus. Data is recorded as per step 4.
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Definitions of Load, Deflection and Specimen Span:
Original position of glass sample
Load: The maximum force
Bibliography: Dowling NE (2007) Mechanical Behaviour of Materials 3 Ed. Pearson Prentice-Hall: New Jersey. Breburge B (1999) Cracks and Fracture. Academic Press: California. Gross D and Seeling T (2006) Fracture Mechanics with an Introduction to Micromechanics. Springer: Berlin. th Callister WD (2007) Materials Science and Engineering 7 ed. John Wiley and Sons, Inc: York. rd Page 7 of 7 G Rezk SID 199991603