Journal of Reinforced Plastics and Composites

This article aims to obtain damage-tolerant designs with minimum weight for a laminated composite structure using genetic algorithm. Damage tolerance due to impacts in a laminated composite structure is enhanced by dispersing the plies such that too many adjacent plies do not have the same angle. Weight of the structure is minimized and the Tsai–Wu failure criterion is considered for the safe design. Design variables considered are the number of plies and ply orientation. The influence of dispersed ply angles on the weight of the structure for a given loading conditions is studied by varying the angles in the range of 0°–45°, 0°–60° and 0°–90° at intervals of 5° and by using specific ply angles tailored to loading conditions. A comparison study is carried out between the conventional stacking sequence and the stacking sequence with dispersed ply angles for damage-tolerant weight minimization and some useful designs are obtained. Unconventional stacking sequence is more damage tolerant than the conventional stacking sequence is demonstrated by performing a finite element analysis under both tensile as well as compressive loading conditions. Moreover, a new mathematical function called the dispersion function is proposed to measure the dispersion of ply angles in a laminate. The approach for dispersing ply angles to achieve damage tolerance is especially suited for composite material design space which has multiple local minima.

A series of low-velocity drop-weight tests were conducted on glass/epoxy laminates to study the effect of multiple non-coincident impacts on residual compression and flexural properties. The impact characteristics and residual properties were recorded to determine the damage tolerance to various impact energies and impact separation distances. A flexure after impact method was also developed and compared to the compression after impact test. Experimental results were combined with a finite element model of the test. The damaged region was modeled as an elastic inclusion of reduced stiffness resulting in a stress concentration that was used to predict residual strength. Post-impact tests and stress analyses revealed that damage size, inclusion stiffness, and strength reduction were sensitive to impact energy and impact separation distances. Multiple impacts at larger distances create distinct, non-interacting damage regions that cause no more reduction in residual properties than the damage regions from a single impact. However, with a small separation distance, the damage regions from multiple impacts overlap and display increased energy absorption and reduction in the residual mechanical properties.

Assembled 3D high-density polyethylene honeycomb cells, providing confinement to arrest spreading of the soil in cells and creating relatively stiff bed that redistributes footing pressure over wider area, were used in the present study to enhance load-carrying capacity and to reduce settlement of base materials under a foundation. The effects of various test parameters including width, height, number of layers of the 3D honeycomb cells, vertical distance between layers of the cells and depth of stress zone of the foundation were studied. The test results indicated that considerable improvement in the load-carrying capacity (≅3.0) and reduction in settlement of the foundation (≅62%) were obtained with the implementation of the single layer of the 3D cells into cohesionless soils. The optimum effective distance between two layers of the 3D cells was 0.142 times the width of foundation, the ratio of effective width of 3D cells to the foundation was about 4.2 and the depth of influence stress zone of the foundation was about two times the width of the foundation.

Carbon/carbon composites were prepared by thermal gradient chemical vapor infiltration with kerosene as precursor. The microstructure and electrical resistivity were examined by polarized light microscopy and low-resistance instrument, respectively. The effects of processing parameters on microstructure as well as the influences of sample density, processing parameters, and needle punch on electrical resistivity of carbon/carbon composites were analyzed. The results show that besides rough laminar, smooth laminar and isotropic pyrocarbon occur at temperatures of 1000°C and 1200°C, respectively. The graphitization degree of composites increases from 16.28% to 63.95% as the heat treatment temperature increases from 2100°C to 2500°C. The electrical resistivity of carbon/carbon composites decreases with increasing heat treatment temperature and sample density but increases as the texture of pyrocarbon varies from rough laminar to smooth laminar. The main mechanism for influencing the electrical resistivity of carbon/carbon composites can be changing carrier concentration, altering grain scattering, or both actions.

This paper aims to investigate the effect of bond strength of corroded steel rebar embedded in concrete cylinders enveloped externally using hybrid and non-hybrid fiber reinforced polymer (FRP) reinforcement. A series of 16 concrete cylinders (i.e. 100 mm × 200 mm) embedded with steel rebar were prepared in the laboratory condition. The test variables were types of fiber reinforced polymer wrapping (i.e. hybrid and non-hybrid fiber reinforced polymer reinforcement), duration of corrosion activity, and percentage of mass loss in steel rebar. The specimens were immersed in 5% NaCl solution at a depth of 170 mm and anodic current was impressed through the rebar for accelerating the corrosion activity. After the exposure period of 24 days, the embedded steel rebar in concrete cylinder was pulled out monotonically to failure. The bond strength, percentage of mass loss in embedded steel rebar, and effect of different periods of corrosion activity on concrete cylinders enveloped with hybrid and non-hybrid fiber reinforced polymer reinforcement are addressed. Test results show that the observed bond strength of hybrid fiber reinforced polymer confined specimens was the highest as compared to the non-hybrid CFRP and GFRP confined specimens. Moreover, the bond strength performance of hybrid FRP confined specimens was slightly better than the non-hybrid CFRP confined specimens.

There is a considerable amount of waste produced daily from processing old corrugating containers. Dumping this waste product incurs a considerable cost to a paper recycling mill. In this study a sample of waste containing 45% fibrous and 55% non-fibrous solid was collected from an old corrugating containers paper-recycling mill and analyzed in a laboratory. The waste was used to produce wastes-urea formaldehyde composites and wastes-polyethylene composites. Physical and mechanical properties of the resulting manufactured panels were compared with commercially produced medium density fiberboard and particle board. The results presented the possibility of panel production from waste, even without inclusion of any additional material. Additives would obviously enhance the physical and mechanical characteristics of a product to render it more competitive with commercially produced panels. The results also revealed that water absorbability and thickness swelling of panels were much less compared with similar commercially available products. The mechanical characteristics of the manufactured panels were weaker relative to the commercially available ones, probably due to differences in density and thickness. Hence, wastes-urea formaldehyde composites and wastes-polyethylene composites panels can be recommended for application if physical properties are more important than mechanical properties.