Dynamic failure of borosilicate glass under various loading conditions

Xu Nie, Purdue University

Abstract

Threats from Improvised Explosive Devices (IEDs) and other small arms such as armor piecing bullets posed significant challenges to light-weight vehicle armor protection, especially the window armor protection, since the windows are one of the most critical but yet vulnerable parts in an armor vehicle. However, existing knowledge of the dynamic behavior of glasses, which is of key importance to understand the penetration process and thus to optimize the effective armor design, is unsatisfactory due to the lack of reliable experimental techniques to characterize the response of glass armor materials under impact loading conditions. In this thesis, a series of experimental methods based on the Kolsky bar technique were established to study the stress state and temperature dependence of dynamic failure and fracture for a borosilicate glass with a variety of surface conditions. The purpose of each experimental method is to evaluate one or several loading conditions that the armor target could have involved during the penetration process. Quantitative compressive strength values are obtained as a function of stress states through the specimen geometry design. Shear stress is introduced and its effect on the equivalent failure strength was investigated by a “hybrid” experimental and numerical method. The crack propagation under the proposed compression/shear stress state is found to follow the maximum compressive principal stress direction. The dynamic flexural strength of borosilicate glass is studied via both four-point bending and ring-on-ring equibiaxial bending techniques. Variation in the flexural strength of more than an order of magnitude is achieved through proper surface treatments, and the mechanisms are explained on the basis of surface defects morphology. In the last part of this research, the temperature effects on the dynamic response of both intact and damaged borosilicate glass are investigated. The surface defect and the dynamic flexural strength of glass are found to be a function of temperature. Residual stress relaxation and crack healing/blunting are identified as the strengthening mechanisms in different temperature ranges; however, little temperature effect is found on the compressive response of damaged glass under mechanical confinement.

Degree

Ph.D.

Advisors

Chen, Purdue University.

Subject Area

Aerospace engineering|Mechanical engineering|Materials science

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