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Cracking of Laminated Glass Initiated by Low Velocity Impacts

Coward, D. P. (2001). Cracking of Laminated Glass Initiated by Low Velocity Impacts. (Unpublished Doctoral thesis, City, University of London)


The work presented in this thesis is concerned with the determination of the relationship between low velocity impacts and the failure by cracking of 420mm square, 6.4 mm thick, three ply, laminated glass. An hydraulic test rig has been constructed which allows tests involving impacts with pre-determined velocities, up to 7 m/s, and deflections, up to 4.6mm, to be conducted upon the glass samples.

Weibull’s approach to describing the failure of brittle materials has been adopted. A Weibull cumulative distribution, which relates the probability of failure to the applied stress, has been generated from the experimental data, and the Weibull modulus or flaw density parameter has been determined to be 3.5.

The stress intensity factor, K or fracture toughness value, is an indication of the toughness of a material. Glass, as a brittle material would be expected to have a low fracture toughness. Values for K can be determined experimentally, and as a material characteristic should not vary widely, however the value of 0.46 MPa m^1/2 for the fracture toughness, obtained dynamically in this work, appears to differ from those figures determined by others, using quasi-static loading, of between 0.7 and 0.8 MPa m^1/2. If the value for K determined during quasi-static loading is applicable to this work, then the length of surface cracks in the glass is calculated to be between 55 and 72 x 10(^-6) m.

The stresses generated during the dynamic loading of glass by an impact can be divided into two distinct elements, the stresses produced by the bending of the glass, and the stresses generated during the impact. However, although the resulting stresses can be described separately, they have a combined effect upon the glass. The stress combination factor / is used to describe how the bending stresses and the impact stresses combine to occasion a micro-crack (which may be found on all exposed glass surfaces) to propagate and cause a fracture in the glass. The value of/is considered to be between 0.7 and 0.8.

Publication Type: Thesis (Doctoral)
Subjects: T Technology > TA Engineering (General). Civil engineering (General)
Departments: School of Science & Technology > Engineering
School of Science & Technology > School of Science & Technology Doctoral Theses
Doctoral Theses
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