Compression of Ceramics

Experimental observations indicate that, in general, the true stress-strain curves of ductile materials coincide. Brittle materials, among them brittle ceramics, do not show a similar behavior. Usually, experimental observations indicate that brittle materials are stronger under compression than under tension. 

Almost all materials are candidates for compression tests. Thus, ductile metals used for various applications, when shaped by forging, drawing, extrusion, etc., 

True stress-strain curves of tension and compression have been experimentally observed to coincide. Yet, this observation is not tme for brittle materials (that behave like glass), in which fracture and yield stress coincide. Thus, in brittle materials, e.g., ceramics, the strain seldom exceeds 1 %, depending to a large degree on the type of deformation involved. Classical Hookean behavior is observed in such brittle materials. The presence of imperfections of various kinds, including porosities, has a profound effect on the mechanical behavior of ceramics. 

Uniaxial compression tests may be done either on unconiined or confined specimens. Unconfined uniaxial tests of porous calcium phosphate ceramics (intended for use as a bioceramic body part) are shown in Fig. 1.43. 

Uniaxial and triaxial compression tests of silicon-carbide ceramics under quasistatic loading conditions were performed by Brannon et al. [33]. Their SiC-N specimens were prepared in the form of a right circular cylinder, as is indicated schematically in Fig. 1.43a next to the experimental set-up. 

---

CRUSHING ROLLS (q.v.) arranged above one another, the upper pair acting as a primary crusher and the lower pair as a secondary crusher. Compound rolls find use in the size-reduction of brick clays. Compressibility. The compressibility of ceramic fibre is the percentage relaxation after 5min of the pressure which gives a 50% reduction in thickness. Cf. RESILIENCE. BS 1902 Pt section 8 specifies tests. 

---