Compression load-strain during

Figure 10. Comparison of the load-strain curves of cartilage during confined and unconfined compression. (Mean values of 12 runs 1 SD.)...

During compression, the loads Increased at Increasing rates with strain until compression ceased. Thereafter a sharp and rapid dissipation of the load was observed. This decreased at decreasing rates with time until time invariant values, characteristic for a given strain, but Independent of strain rate, were attained. During unconflned compression the loads Increased to lesser extents for the same axial displacements, and relaxation was considerably slower. Against our most porous platen, the load-strain curves had little, if any, strain rate dependence. Plots of the mean loads at each strain against the porosities of the platens resulted in a family of linear curves that extrapolated to approximately the same porosity at low loads. 

The CTH approach is able to control the crack width, which can be closed by controlling the compression pre-strain level. A simple equation has been established by Li et al. [54] to correlate the crack width to be closed and the pre-strain level during compression programming. Cracks with different opening widths can be closed based on the level of compression programming (of course it is limited by the maximum allowed compression pre-strain level). In the unconstrained shape recovery approach such as the SMASH approach, it has not been demonstrated that it can close a wide-opened crack with constrained boundary. Also, it cannot control the crack width that can be closed because it depends on the external load to perform programming and relies on the shape recovery ratio and boundary condition of specimens to perform crack closing. 

For compressive stress-strain, the test specimen is placed between load columns in the furnace. A dilatometer system, to which the extensometer is attached, is located in the test specimen as shown. Other arrangements may use optical or averaging extensometers. This means the specimen deformation and hence strain can be measured. It is important to load the specimen slowly during the test to simulate the slow stress build due to thermal expansion in a refractory lining. 

---