Mechanical strain with radiation

The nano modified PDMS systems discussed have properties that enable a more confident prediction of ageing trends. The properties of the carborane modified system change in a linear fashion with radiation dose as opposed to the nonlinear trend observed for conventional particulate filled PDMS. The silica and carbon nano tubular systems display simplified mechanical properties. The reduction in Mullins effect or move to a more linear, less complex stress strain behavior, allows increased accuracy in property measurements. 

Above a certain degree of crosslinking, strain at break and impact strength decrease again, and the plastic becomes hard and brittle. Radiation-chemical degradation also causes a decrease in mechanical properties with increasing radiation... 

Nobumichi Tamura (left) obtained his Ph.D. in 1993 at the Institut National Polytechnique de Grenoble (INPG) for his work on the structure of quasicrystals and crystalline approximant phases. In 1998 he moved to Oak Ridge National Laboratory to contribute to the development of a new synchrotron-based X-ray microfocus technique capable of resolving strain and texture in thin films with submicrometer spatial resolution. He applied this technique in the field of microelectronics. He is currently staff scientist at the Lawrence Berkeley National Laboratory, where he leads the X-ray microdiffraction project at the Advanced Light Source. His research interest is presently focused on the study of mechanical properties of thin films at mesoscopic scale using synchrotron radiation. 

The mechanical properties, fiacture stress, fiacture strain, yield stress, and modulus, were measured (67) for doses up to 100 Mrads. Fracture strain was found to increase with dosage but shear yield strength decreased. Decreases averaging roughly 50% were noted for the other properties. Therefore, it is evident that the -radiation produces a predominance of chain scission over crosslinking in the epoxy. It was concluded that irradiation does not have much effect on the graphite fibers but that it degrades mechanical properties of the epoxy matrix. 

Different modes of damage are possible as a result of the mechanical tests. It is necessary to consider the results of these modes for any analytical assessment to demonstrate compliance with the applicable requirements. The fracture of a critical component or the breach of the containment system may allow the escape of the radioactive material. Deformation may impair the function of radiation or thermal shields and may alter the configuration of fissile material and it should be reflected in the assumptions and predictions in the criticality assessment. Local damage to shielding may, as a result of the subsequent thermal test, give rise to deterioration of both thermal and radiation protection. Consequently, investigations should include stress, strain, instability and local effect for all attitudes of drop where symmetry does not prevail. 

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