Permanent material

As reviewed thermoplastics (TPs) being viscoelastic materials respond to induced stress by two mechanisms viscous flow and elastic deformation. Viscous flow ultimately dissipates the applied mechanical energy as frictional heat and results in permanent material deformation. Elastic deformation stores the applied mechanical energy as completely recoverable material deformation. The extent to which one or the other of these mechanisms dominates the overall response of the material is determined by the temperature and by the duration and magnitude of the stress or strain. The higher the temperature, the most freedom of movement of the individual plastic molecules that comprise the... 

Inspection of substrate for permanent materials for corrosion can be difficult. 

With the exception of sodium silicate grout gelled with a bicarbonate (such as sodium bicarbonate), all chemical grouts subsequently discussed are generally considered to be permanent materials. 

Gelled soils under the water table which are not subject to alternate wet-dry or freeze-thaw cycles have good stability. Under these conditions, the lignosulfonates are considered permanent materials. However, they respond very quickly to wet iry and freeze iry conditions (Fig. 11.37) and should not be used under these conditions for permanent installations. 

Table 2 shows the quantity of the major permanent materials installed in the plant including materials used in construction in New Zealand and in the preassembly yard in Japan. 

Yield stress Stress level at which permanent material deformation begins. 

Many properties of liquid paints can be measured with considerable accuracy. Samples must be homogeneous. They must also be sufficiently large to be representative for a given batch. Impurities and permanent material defects (e.g., skin formation, a hard sediment, or gelling of the paint) can be detected. The most common investigations to which a sample is subjected before starting the tests are described in ISO 1513. Only those tests that are important for paint storage, transportation, and application are described here. 

Simple pontoons arc also extensively used on marine construction sites as transport for temporary and permanent materials and as working platfonns for lifting and/or pile driving. Uniflotcs or equivalent can also be joined together to make platfonns of any size and shape to fit around or between construction works. 

It is a fundamental assumption of material behaviour that for short term loading the material is linear elastic to ultimate failure. Under long term loading the material is linear visco elastic with recovery on removal of load, providing the strain does not cause permanent material deterioration. 

Stability of permanent material Nonresorbable fibrous materials that have to keep integrity during the whole implantation duration are characterized by chemical stability and low amount of release. This could be achieved through appropriated materials nature, such as PET previously introduced, or materials surface passivation. 

Potential breakdown of permanent material Simultaneously, to induce no release of chemical components, permanent materials have to undergo repeated physical and mechanical stress transferred by the biological environment to the implantable medical device. Although long service lifetime of the material is expected, these stresses may result in strucmral failure of the implant and particle release firom the fibrous material in the biological environment. 

Permanent materials could be thus designed to provide smart fibrous implantable medical devices with improved performance and decreased amount of particle release to give better biocompatibihty. 

The dehydration of membrane may result in temporary performance losses in addition to permanent material damage [36]. 

---