Stress-Strain Modeling of Polypropylene Composite

Abstract The strain rate dependency of the initial modulus ( E i ), secant modulus at yield (E o ), and of the yield stress, ( y ), of glass fiber reinforced polypropylene (GF-PP) were investigated and modeled along with the stress strain relationship. The GF-PP had a density of 1940 kg/cm 3 . The tensile test specimens were directly machined out of the pipe insulation system. The strain rate, , of loading was varied from 0.30%/min to 35%/min. The stress strain relationship of the composite polymer in tension was elasto plastic with hardening and a stress strain model was used to predict the behavior

Fracture and Viscous Behavior of Polypropylene Composites Coating Insulators for Deep Water Oil Pipelines

Over the past few decades, polymer composites are being used as subsea insulation coatings material in deep water oil pipelines. Failure of the insulation coating materials can significantly affect oil production. The major objective of this study was to characterize the physical and mechanical properties and quantify the effect of crack, strain rate and temperature on the visco-elasto-plastic behavior of the ductile polypropylene polymer (PP) with and without glass fillers in tension, compression, shear and bending. The density of the composite materials studied varied from 0.79 to 1.90 g/cc. The thermal conductivity of the coating insulators varied from 0.140 to 0.306 W/m.K. The effect of strain rate (ε ̇) and temperature (T) on the nonlinear visco-plastic stress-strain behavior, yield strength (σy), initial elastic modulus (Ei) and secant modulus at yield (Esy) of the materials (unfilled polypropylene, polypropylene with 65% glass filler and polypropylene with glass microsphere filler) was characterized and modeled. The tensile yield strengths of the materials varied from 3 to26 MPa. The rate of change in the tensile yield strength with temperature and strain rate were directly proportional to the yield strength and inversely proportional to the strain rate respectively. Crack growth and propagation in the multilayered polypropylene composite coating was investigated using the three dimensional Digital Image Correlation (3D DIC). Also the strain field (ε) development around the crack tip was investigated. A new concept based on Mode 1 strain rate amplification factor (γι) was introduced to model the behavior of polymer composite with crack that increased the tensile yield strength, initial modulus and secant modulus at yield but reduced the strain energy density, at yield and failure, and the ductility making the ductile coating materials stronger but more brittle. A three parameter constitutive relationship for polymer composites was developed to model the nonlinear visco-elasto-plastic and strain softening/hardening behavior of the polypropylene composites coating materials in function of strain rate (ε ̇) and temperature (T).Civil and Environmental Engineering, Department o

Geotechnical Properties of Marine and Deltaic Soft Clays

More and more construction projects are encountering soft clays and hence there is a need to better quantifying the properties of soft clays. In this study, physical, index and strength properties of marine (different parts of the world) and deltaic soft clays (Houston, Texas) were determined using the soft soil database developed from the published data in the literature. Data was analyzed using statistical methods (mean, standard deviation, variance and probability density function). Based on the coefficient of variation (COV), the deltaic deposit from one location showed greater variation in the index properties than the marine deposits collectively. Although the undrained shear strengths for both deposits were beta distribution the COV for the undrained shear strength for the marine and deltaic soft clays were 38% and 26% respectively. The linear relationship between undrained shear strength (Su) and preconsolidation (σp) was verified for the marine clays. A new relationship between undrained shear strength (Su) and in-situ vertical stress (σv) has been developed for the soft clays. Also constitutive models used for predicting the soft soil behavior have been summarized

Stress and Stress Path Dependence of the Recompression Index (C r ) for an Over Consolidated Clay Soil

Abstract: This study focused on the methods of determining the recompression index (C r ) of an over consolidated clay soil in Houston, Texas. Based on the method used to determine the C r , up to 300% difference in the minimum and maximum C r values was observed

Recompression Index (Cr) for Overconsolidated Soft Clay Soils

Overestimation of settlement on overconsolidated soft clays may require ground improvement before construction with added delay and cost to a project. Since the soft soil shear strength is low, the structures on the soft soils are generally designed so that the increase in stress is relatively small and the total stress in the ground will be close to the preconsolidation pressure. Hence the recompression index, determined from a consolidation test is very important parameter in estimating the settlement. Although recompression index has been quantified in the literature, its determination may not be applicable to all soft soils in its current form. The influence of stress level on the recompression index is not clearly quantified. This study focused on developing methods for determining the recompression index of overconsolidated soft clay soils. Based on the methods used to determine the recompression index, over 750% difference in the minimum and maximum Cr values was observed for the Houston area soft clay. Effect of applied stresses on the recompression index was also investigated