h. adibi

Ceramic Matrix Composites (CMCs) are designed to overcome the main drawbacks of monolithic ceramics, especially their brittleness, in high-performance and safety-critical applications. Owing to the inherent properties of CMCs, especially heterogeneous structure, anisotropic thermal and mechanical behavior, and the hard nature of fibers or matrix, the machining process becomes extremely challenging as the generated surface suffers from undesirable quality. Taking the high hardness of ceramic matrix into account, grinding with diamond abrasives is the only efficient way for machining of CMC materials. The aim of this paper was to study the influence of grinding parameters (cutting speed, feed speed, and depth of cut) and different cooling-lubrication conditions (i.e. dry, fluid, and minimum quantity lubrication) on surface roughness, process efficiency, and tool wear. The results indicated that MQL leads to the best results in terms of surface quality and process performance. Furthermore, increasing of cutting speed and feed speed decreased and increased surface roughness, respectively, while depth of cut had an insignificant effect on the roughness value. Regarding the experimental results, four machining strategies considering quality, productivity, and efficiency criteria were developed. Eventually, the material removal mechanism was evaluated using SEM photos, indicating that brittle fracture is the dominant removal behavior of CMC materials.

Quantitative Ultrasound (QUS) is a noninvasive and inexpensive portable method for bone mineral densitometry (BMD). QUS measures some other parameters like elasticity and microarchitecture in addition to BMD. This study designed to determine the normal values of QUS parameters (SOS, BUA and SI) of the calcaneus in a normal population of Tehran.

BMDs of the heel in 259 normal men and women, 20 - 76 Y/O (participant of the Iranian Multicenter Osteoporosis Study (IMOS) were assessed using Achilles+ (a QUS device from Lunar corp.) After assessment of normal values, Stiffness Index (SI) percentiles (2.5, 50, 97.5) in men and women were established.

Mean values of SOS, BUA and SI in women were s36/75±1527/25, 121/42±15/1, 94/46±17/92 respectively and in men were 1553/63±43/20, 127/80± 13/09, 100/19±18/77 respectively. Mean of SI in men and women 20 - 40 Y /0, had no significant difference with reference data used for QUS device. On the other hand there was a good correlation between diagnostic groups in reference values and results of our study (K= 0/875). Relation between age and sex and QUS parameters was significant.

Results of this study show a good correlation between normal values of QUS of an Iranian population in this study and reference values of the American and European populations.