Prashant Kumar

Comparative study of carbon fabric reinforced and glass fabric reinforced thin sandwich panels under impact and static loading

Glass fabric reinforced thin sandwich panel and carbon fabric reinforced thin sandwich panel of thickness close to 2.5 mm were studied to explore an alternative skin material for the outer body of various machines and appliances. The polyester foam Coremat XM of 2 mm thickness was used as core material in the thin sandwich panels. The panels were fabricated by vacuum bagging process and characterized through two plate tests: (i) low-velocity normal impact loading under a drop weight impact test set up and (ii) transverse static loading of a plate. The damage area, indentation depth and permanent depression over damage area, energy absorption capability, load-deflection relation and failure modes were observed under the test. The impact drop test was simulated by LS-DYNA. The properties of glass fabric reinforced thin sandwich panel and carbon fabric reinforced thin sandwich panel were compared with those of 0.8-mm-thick MS sheet, a widely used skin material for the outer body of various machines and appliances.

Experimental studies on thin sandwich panels under impact and static loading

Several thin sandwich panels (thickness close to 3 mm) of different configurations were studied to explore an alternative material for the outer body of various machines and appliances such as automobile, refrigerator, washing machine, lathe machine, drill press, cupboards, light furniture, etc. Three types of sandwich panels with the outer face sheets made of glass fabric/epoxy were fabricated for the present study: (1) XM-Core panel was made of polyester foam Coremat XM/epoxy as core material, (2) Xi-Core panel was made of polyester foam Coremat Xi/epoxy as core material, and (3) J-Core Panel was made of layers of Jute fabric/epoxy as core material. A very thin transition layer of glass chopped strand mat/epoxy was provided between the face sheets and the core to improve their bonding strength. The sandwich panels were analyzed for low velocity normal impact loading under a drop weight impact test set up and transverse static loading under universal testing machine. Damage area, indentation depth and permanent depression over damage area, and failure modes were observed under incident impact loading. The transverse static test was performed to observe load versus deflection relation and to characterize the flexural strength and stiffness.

Experimental study of CFRP patches bonded on a cracked aluminum alloy panel

An experimental study was conducted to arrest a crack in 1.0-mm-thick 6061-T6 aluminum single-edge-notch tension specimen. The specimen was repaired by symmetrical bonding of carbon fiber-reinforced polymer patches made of several plies. Although J-integral was reduced drastically, the specimen failed at one of the leading edges through separation at the interface. The separation was suppressed by tapering all the four leading edges of the patches. The specimens did not fail in the patched area when loaded up to the far field stress of 272 MPa, which was higher than the yield stress, 265 MPa of the aluminum plate.

Optimizing the size of a CFRP patch to repair a crack in a thin sheet

ABSTRACT One of the several techniques to repair cracks in structural sheets consist in bonding polymer composite patches. The effectiveness of the repair for restoring the quasistatic strength of the structure depends largely on the adhesively bonded interface. The interface fails due to interfacial separation caused by the high peeling and shearing stresses. The geometrical dimensions, that is, patch length and width, have significant effect on the interface separation and they need to be optimized. The failure strength of the patch was determined by a numerical analysis using the cohesive zone model. Twenty-five numerical analyses were carried out as per the L-25 Taguchi orthogonal array followed by ANOVA which indicated the greater contribution of the patch width toward the failure of the patch. The failure stresses thus obtained were used to generate a response surface in ANSYS Design Explorer Module. A design criterion in terms of the percentage increase of the failure stress over the yield stress of the skin was used for minimizing the area of the patch. The optimum length and width of the patch corresponding to the minimum patch area were obtained by plotting the response curves generated from the response surface.

The role of yield stress on cracked thin panels of aluminum alloys repaired with a fRP patch

ABSTRACT The aim of this study was to explore the effect of the yield stress of the cracked thin panels of aluminum alloys panel, repaired with one sided fiber reinforced polymer (FRP) patch, on the performance of the repair. Various different grades of aluminum alloys with thickness in the range of 1–1.3 mm were used as the skin material. The numerical simulation of the experimental results was done through ANSYS 15.0, using a cohesive zone material model (CZM model) at the interface of the skin and the patch. The effect of the far field applied stress was analyzed to simulate the initiation and the separation of the patch. In all the six cases, undertaken in this study, the patch separation occurred when the applied stress exceeded the yield stress of the skin by a small percentage. Even in the thinnest patch with its stiffness ratio of 0.28, the patch separated when the applied stress exceeded the yield strength of the skin material. In all the cases, the shear stress at the interface caused the slippage between the patch and the skin at the leading edge of the patch.

Characterization of GFRP butt-joint under tensile and flexural loading

A GFRP butt-joint was formed between two adherends of an aluminium pipe by winding a wetted roving of glass fiber with epoxy at ±45° angle. The butt-joint was studied through two kinds of tests: tensile and bending. The specimens were of two types: thin and thick GFRP sleeve. In tension tests, the thin sleeve specimens failed due to the failure of the GFRP sleeve at the joint plane as the axial stress developed in the GFRP sleeve exceeded its ultimate strength. However, the thick sleeve specimens resisted higher load but one of the two adherends slipped out of the GFRP sleeve. In bending experiments, the failure in specimens with a thin GFRP sleeve occurred due to the breakage of the sleeve at the joint plane. However, the specimens of thick GFRP sleeve did not fail within the sleeve. Numerical analysis using ANSYS was carried out to explain the experimental results.

Experimental Study and Numerical Analysis of a CFRP Butt-Joint between the Pipes of Dissimilar Materials

A butt-joint was formed between two pipes of dissimilar materials, steel and aluminum, by winding a wetted roving of carbon fiber with epoxy at ±45° angle. On the curing of the epoxy, a tight carbon fiber reinforced polymer (CFRP) sleeve was formed, joining the ends of the pipes. The CFRP butt-joint was characterized for two kinds of loads: tensile and bending. Based on the joint strength performance, the specimens were categorized into two groups, thin and thick CFRP sleeved specimens. In the tensile testing, the thin sleeved specimen failed through the breakage of the CFRP sleeve at the joint plane because the axial stress developed in CFRP sleeve exceeded the ultimate strength of the CFRP. However, the thick sleeved specimens resisted the axial load in the sleeve and the weaker adherend, the aluminum pipe, slipped out of the CFRP sleeve. In the flexural testing, the thin CFRP sleeved specimens also failed by failure of the CFRP sleeve at the joint plane while the specimens of thick CFRP sleeve failed by the formation of a plastic hinge near the edge of the CFRP sleeve.