Structural Arrangement Effects of Mineral Platelets on the Nature of Stress Distribution in Bio-Composites

Bone is a hierarchical bio-composite, and has a staggered arrangement of soft protein molecules interspaced with hard mineral platelets at the fine ultrastructure level. The investigation into reasons for high fracture toughness of bio-composites such as bone requires consideration of properties at the different levels of hierarchy. In this work, the analysis is done at the continuum level, but the properties used are appropriate to that of the level considered.

In this way, the fine ultrastructure level of bone (refer Figure 1) is considered and the analysis of the stress distribution in platelet 2 adjacent to the broken platelet 1 within a staggered arrangement is undertaken. Results (refer Figure 2) show the influence of overlapping ratio, (OR=L/t) in determining the nature of stress distribution, where t is the width of the platelet.

In this work shear lag theory is used for analysis. The stress is higher at the end of the platelet 2 and lesser at the centre for low OR whereas the stress is higher at the centre and lower at the ends for high OR. Hence it is expected that overlapping ratio may play a role in the fracture toughness of bio-composites.

 S. Anup, S.M. Sivakumar & G.K. Suraishkumar

A Study on Shape Control of Composite Structures Embedded with Shape Memory Alloy Wires.

Shape memory alloys are metal alloys that exhibit the special characteristics of either large recoverable strains or large induced internal forces under load and /or temperature changes. The unique thermo mechanical properties of SMAs are due to a crystallographic phase transformation from the austenite/parent phase to the martensite / product phase or vice-versa. These transformations can be induced by changes in stress or temperature alone or combination of both. SMAs appear to have significant advantages for structural response control, structural shape control and damping enhancement. There are strong demands for materials that have the high mechanical properties (i.e., stiffness, yield stress and fracture toughness). The composite materials made of smart materials have the characters that satisfy above requirement. Therefore, studying the composite materials is very important since such composite materials can allow us to create safer environment.

Shape Memory Alloys (SMA) with abilities to change their material properties such as Young's modulus and the generation of large internal forces, when integrated with composite material structures allow active control of their static and dynamic behaviors. The micromechanical behavior of SMA fibers in homogeneous elastic matrix is studied and analytical homogenization procedure is used to evaluate the overall response of the composites. Concerning the analytical approach, a classical homogenization procedure, the self-consistent approach, appear to be suitable to derive the overall response, as the volume fraction of the SMA fiber in the composite generally assumes very low values.

 K.Pazhanivel and S M. Sivakumar