Spring back effect

Bending (Sheets), Fig. 5 Qualitative stress distribution in x direction over the sheet thickness during loading (/ ), spring back effect (middle) and resulting residual stresses (right)... 

After arriving at the maximum pressing force, pressure is released. If as shown in Fig. 8.1, compaction is performed by a punch in a die, the direction of travel of the piston reverses and, when no expansion of the densified body occurs, the pressing force should drop to zero immediately (vertical line). In reality, there is always a more or less pronounced spring-back which is caused by the expansion of compressed gas and the relaxation of elastic deformation. As mentioned before, this effect becomes more pronounced with increasing speed of densification until, at a certain compression rate, the compacted body disintegrates partially or totally upon depressurization. Therefore, it is often necessary to find an optimal compromise between densification speed (= capacity) and product integrity (= quality). 

Fig. 5.9 (Chapter 5) depicts in its entirety the force or pressure diagram of a typical cycle of high-pressure agglomeration as a function of time. The effect of the two phenomena that are responsible for most problems associated with this technology, expansion of compressed air and/or elastic spring back, are shown to occur after having reached and take some time. The more important changes caused by these phenomena, however, are an increase in volume and porosity (Fig. 5.9) and the potential lowering of the product s structural integrity. In the best case, they will (only) lead to reduced strength, which may be corrected by a suitable post-treatment (e.g., coating.

Question by M. P. Erhard, Douglas Aircraft You mentioned that a decreasing load shows a higher thermal conductivity than an increasing load. Were you able to correlate this with your thickness measurements It appears that this effect might be due to hysteresis wdth the sample not springing back to its original shape. 

The ability of a system, community or society exposed to hazards to resist, absorb, accommodate to and recover from the effects of a hazard in a timely and efficient manner, including through the preservation and restoration of its essential basic structures and functions. Resilience means the ability to resile from or spring back from a shock. The resilience of a community in respect to potential hazard events is determined by the degree to which the community has the necessary resources and is capable of organizing itself both prior to and during times of need. 

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