Shear Stress In Adhesive Layer Research Articles

Performance of steel beams strengthened with pultruded CFRP plate under various exposures

The use of Carbon Fiber Reinforced Polymer (CFRP) to strengthen steel structures has attracted the attention of researchers greatly. Previous studies demonstrated bonding of CFRP plates to the steel sections has been a successful method to increase the mechanical properties. However, the main limitation to popular use of steel/CFRP strengthening system is the concern on durability of bonding between steel and CFRP in various environmental conditions. The paper evaluates the performance of I-section steel beams strengthened with pultruded CFRP plate on the bottom flange after exposure to diverse conditions including natural tropical climate, wet/dry cycles, plain water, salt water and acidic solution. Four-point bending tests were performed at specific intervals and the mechanical properties were compared to the control beam. Besides, the ductility of the strengthened beams and distribution of shear stress in adhesive layer were investigated thoroughly. The study found the adhesive layer was the critical part and the performance of the system related directly to its behavior. The highest strength degradation was observed for the beams immersed in salt water around 18% after 8 months exposure. Besides, the ductility of all strengthened beams increased after exposure. A theoretical procedure was employed to model the degradation of epoxy adhesive

Optimization of circular composite patch reinforcement on damaged carbon fiber reinforced polymer laminate involving both mechanics-based and genetic algorithm in conjunction with 3D finite element analysis

Composites are significantly used in aerospace, automotive and civil structures due to their high specific strength, high stiffness, corrosion resistant and longer fatigue life. During service life, composite structures are susceptible to damage, which reduces their structural integrity. For extending its service life, the damage needs to be repaired. In case of low velocity impact damage adhesively bonded patch repair is found to be effective in extending the service life of damaged parts. The repair performance is mainly influenced by patch stacking sequence, patch shape, patch thickness, overlap length and adhesive thickness and its shear strength. In the present work, both numerical and experimental works are carried out to study the mechanics of composite patch repair on damaged carbon fiber reinforced polymer panel of configuration [45/−45/0/90]s subjected to tensile load. The influence of patch stacking sequence, patch thickness, adhesive thickness and overlap length on repair performance is investigated through a mechanics-based design approach involving finite element analysis. Stress concentration factor and shear stress in adhesive layer are considered to analyze the repair performance. Later, a genetic algorithm-based approach in conjunction with finite element analysis is implemented for arriving at an optimized patch dimension and adhesive thickness. Experimental study is then carried out with optimized geometry using non-contact optical-based technique namely digital image correlation. The strain field from digital image correlation is compared against the finite element results.