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Hypothesis: Because of the widespread use of rubbers in different industries, estimating the rubber material properties and its lifetime are very important in design procedure to assure the quality and safety of the rubber components. In this study, the properties and useful lifetime prediction of EPDM rubber parts used in the production of sealing gaskets and sealants for GRP pipes were investigated and the effect of adding silica nanoparticles as well as Si69 coupling agent on these characteristics was studied.

Methods: In this work, the samples were tested under accelerated aging conditions and aged in the temperature range of 25-90 °C until 60 days. Then time-temperature superposition was carried out on tensile test and compression set results using Williams Landel Ferry (WLF) model to estimate useful lifetime of the samples. Tensile test was conducted under ISO 12244 standard and compression set test was performed according to ISO 815 standard on rubber samples. Aging effect on samples with and without silica was analyzed with FTIR. In addition, scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were performed to observe the dispersion condition of silica nanoparticles in EPDM samples.
 
Findings: According to obtained results, TEM images showed no sign of nanoparticles agglomeration within the samples due to presence of Si69 and SEM graphs depicted a uniform distribution of particles in the matrix. Using time-temperature superposition principle, the lifetime was estimated about 63 and 35 years at room temperature for the rubber samples with and without silica and Si69 coupling agent, respectively. It was observed that the presence of modified silica nanoparticles improves the mechanical and thermal properties of EPDM and also increases the useful lifetime of this elastomer.
 

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Abstract: Saturated granular soils are possible liquefied when subjected to earthquake loading. This phenomenon is result from generation of excess water pore pressure because of non enough time to water drainage and govern non- Consolidated Condition. When liquefaction is occurred, many forces are generated and undergrounds structures are affected. In this research numerical analysis on buried pipelines in FLAC 2D software are performed and verified duration a comparative process with experimental result from ASCE organization. In present research surveyed effects of various parameters on liquefaction occurrence and probable damages to buried pipelines as dilatancy and friction angle of soil, relative density of back fill around the pipe, diameter and buried depth of pipe and underground water level. Results indicated that uplift of pipe decrease when dilatancy and friction angle of soil increased in constant relative density condition. This result is different for varied relative density. In low and medium relative density by increasing of dilatancy angle, uplift of pipe increase, reach to pick and decrease. But floating decrease with increasing dilatancy angle for high relative density always. Buried pipe in depth trench and increase of dead load result from back fill on pipeline and usage of pipes with small diameter, decrease uplift the pipe in liquefaction occurrence too. Of course don’t expect perform this subjects in all conditions. for example conflict ion to other underground installation, necessary hydraulic gradient for fluids flow or excavation in region with up underground level, don’t make to excavation of deep conduits. The analysis demonstrate that vertical displacement and damages to pipe is decrease if around installed pipe in conduit back fill with non- liquefied soils. In this new analysis all physical properties of soil and pipe in model are without any change except the cohesion and friction angle of soil around the pipe. Cohesion soils are low potential to liquefaction. For this reason we increase this coefficient from zero to 30 kpa and reach the friction angle to 30 degree. Results are demonstrated in a graph that show uplift versus thickness of non- liquefied soil normalized with diameter of pipe. Final parameter that surveyed in this research is effect of underground water level on floating buried pipeline. Results show decrease of underground water level cause to decrease of floating and damages to pipeline. For this purpose add a new water level to base model and run the analysis. In next steppes the underground water level is lesser and results are show in a graph that explain variation of vertical displacement versus water level normalized by thickness of soil model. This work possible by excavation of drainage shaft and drop down water level nearby the pipeline. Of course, look this work isn’t economical proposal for long transmission pipelines as petroleum or water conveyance. But in limit industrial sites as refineries this proposal is an improvement work to prevent any damage and and continual service of lifelines duration of unpredictable phenomenon. Keywords: Liquefaction, buried pipelines, FLAC, finite difference method, Finn’s model. Liquefaction, buried pipelines, FLAC, finite