Localized surface plasticity

Fig. 2a—c. Schematic drawing of several postulated microscopic steps in craze nucleation a Formation of a localized surface plastic zone and buildup of significant lateral stresses, b Nucleation of voids in the zone to relieve the triazial constraints, c Further deformation of polymer ligaments between voids and coalescence of individual voids to form a void network... 

D. A. Jones, The contribution of localized surface plasticity to the mechanism of environment-induced cracking, in R.P. Gangloff, M.B. Ives (Eds.), Environmental-Induced Cracking of Metals, NACE, Houston, TX, 1990, pp. 265-270. 

In this case, it is also possible to realize patterns of different metals onto the same substrate, preserving the capability to separately control the local surface roughness of each region. Furthermore, this method can be applied to a wide variety of substrates (e.g., silicon, silica, glass, quartz, plastic, etc.), by taking into account eventual differences in the metals adhesion to the substrate and by properly adjusting the SGDR reaction conditions. 

Crack formation increases with the degree of unsaturation. Crack propagation rate decreases with increasing degree of crosslinking critical strain decreases. Crack formation is preferentially Initiated in areas of higher local surface strain. Very high loads of carbon black or other Alters thus can result In intense crack formation. Factors (such as hydrocarbon plasticizers) that increase elasticity also tend to increase crack formation [697]. 

A catastrophic failure of stressed metals in corrosive solutions in comparison with their stable behavior in air can be explained by the synergetic interaction between mechanical and chemical processes described as mechanochemical phenomena [53]. Chemical (electrochemical) reactions proceeding on the metal surface and causing additional dislocation flux and localized enhanced plasticity, affect the fine microstructure and creep properties of a solid. 

In the hot-embossing process a heated die carrying the negative of the conductor layout presses a specially coated copper film on to a thermoplastic substrate, applying thermal loading and mechanical pressure. The die cuts out the film, forming a positive bond to the locally melted plastic close to the surface of the blank. Figure 3.16 shows the process chain in simplified, schematic form. 

The application of load in materials produces internal modifications such as crack growth, local plastic deformation, corrosion and phase changes, which are accompanied by the emission of acoustic waves in materials. These waves therefore contain information on the internal behaviour of the material and can be analysed to obtain this information. The waves are detected by the use of suitable sensors, that converts the surface movements of the material into electric signal. These signals are processed, analysed and recorded by an appropriate instrumentation. 

As two surfaces are brought together, the pressure is extremely large at the initial few points of contact, and deformation immediately occurs to allow more and more to develop. This plastic flow continues until there is a total area of contact such that the local pressure has fallen to a characteristic yield pressure of the softer material. 

Plastic strain localization and mixing due to void collapse in porous materials works in the same way, with perhaps an even greater degree of actual mixing due to jetting, and other extreme conditions that can occur at internal free surfaces in shock-loaded solids. 

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