Hertzian contact response of tailored silicon nitride multilayers
- National Inst. of Standards and Technology, Gaithersburg, MD (United States). Materials Science and Engineering Lab.
The nature and degree of damage accumulation beneath Hertzian contacts in silicon nitride-based laminates are studied. Specimens with alternating homogeneous and heterogeneous layers are fabricated by a tape-casting route, with strong interlayer bonding. Homogeneous material consisting of relatively pure fine-grain silicon nitride is used as the overlayers. Heterogeneous material containing 10 to 30 wt% boron nitride platelets in a silicon nitride matrix, with weak platelet/matrix interphase boundaries, forms the underlayers. Contact tests with spherical indenters are used to monitor the stress-strain response of the laminates and to investigate the damage modes within the individual layers. The heterogeneous layer exhibits a distinctive ``softening`` in the stress-strain curve, indicating a quasi-plasticity in the silicon nitride associated with local microfailures at the platelet/matrix interfaces. In contrast to the well-defined cone cracks that develop within the tensile zone outside the contact area in bulk homogeneous silicon nitride, the damage in the laminates is widely distributed within the shear-compression zone below the contact. Fractures form incompletely in the homogeneous layers, as downward-propagating partial cone cracks and upward-propagating stable cracks. Comparatively extensive, diffuse microscopic damage occurs in the heterogeneous layers, culminating in a macroscopic failure that traverses these layers at higher loads. A strong synergism between the interlayer damage modes is apparent. Implications concerning the design of composite laminates for improved damage tolerance, with retention of strength and wear resistance, are considered.
- Sponsoring Organization:
- USDOE
- OSTI ID:
- 247919
- Journal Information:
- Journal of the American Ceramic Society, Journal Name: Journal of the American Ceramic Society Journal Issue: 4 Vol. 79; ISSN 0002-7820; ISSN JACTAW
- Country of Publication:
- United States
- Language:
- English
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