Papers by Keyword: Delamination

Abstract: In order to effectively describe the damage process of composite laminates and reduce the complexity of material model, a mixed damage model based on Linde Criteria and Hashin Criteria is proposed for prediction of impact damage in the study. The mixed damage model can predict baisc failure modes, including fiber fracture, matrix tensile damage, matrix compressive damage. Fiber damage and matrix damage in compression are described based on the progressive damage mechanics; and matrix damage in tension is described based on Continuous Damage Mechanics (CDM). Meanwhile, for interlaminar delamination, damage is described by cohesive model. A finite element model is established to analyze the damage process of composite laminate. A good agreement is got between damage predictions and experimental results.

Abstract: Malaysian government has already built the first glulam structure in Malaysia with the aim of demonstrating the potentialities of using indigenous hardwood timber for glulam. Since Malaysia possesses a vast variety of timber species, hence there is a need to identify suitable species for glulam manufacturing. This paper presents the bending performance of Malaysian hardwood glulam beams, manufactured from different categories namely heavy, medium and light hardwood timbers. A series of tests were carried out on the glulam beam that includes bending test, delamination test and shear test of glue line. Results in this study will be useful to manufacturers interested in using Malaysian hardwood for glulam beams.

Abstract: Critical strain energy release rate in CFRP composites characterizes the delamination resistance. More study is still needed to measure the critical strain energy release rate in sliding shear mode (G_IIC) considering various factors that influence its measurement. This study evaluates one of the influencing factors, the starter defect. Two types of on thin, unidirectional CFRP composites with one having thin film insert as starter defect and another one with pre-crack under Mode II loading were prepared and tested in three point bending end notch flexure (3ENF) test. It was found that the (G_IIC) of the former was more than twice higher than that of the latter, supposedly due to the presence of resin rich region in the former.

Abstract: Laminated glass which consists of two glass sheets connected to each other with PVB interlayer is used in many engineering applications for years. Despite the long history of the use of laminated glass in buildings there are serious problems about delamination of laminated glass units. This paper provides information about delamination issues of laminated glass plate structures. Delamination of laminated glass unit may be due to the thinning of PVB (Polyvinyl Butyral) interlayer or the folds which occur during the manufacturing process. Laminated glass behaves in a complex manner due to the effect of geometry that undergoes large deflection even under their own weight and the order difference between the elastic modulus of glass and interlayer. Because of the mentioned reasons large deflection analysis has to be performed in the determination of the effect of delamination on the strength of laminated glasses.

Abstract: The present work is devoted to the analysis of a buckling behavior of a cylindrical composite panel. The considered structure is subjected to the uniform axial compression. The wall of the panel consists of the 8 layers. In addition, in the geometrical center of the structure there is a square delamination located between the fourth and the fifth layer. The main goal is to determine the buckling and post - buckling behavior as well as the influence of the delamination on the stability of the structure. The nonlinear numerical analysis is carried out with aid of the FEM method. The experimental verification is also performed. The results obtained from numerical and experimental analysis show very similar behavior of the structure.

Abstract: The purpose of this study was to find experimentally the effects of concave and convex major cutting edge (Helical & Recon point) and chisel point on the drilling composite. Due to composite materials are natural orthotropic, so gradually these materials are substituted by some metals such as steel that are used in manufacturing automobile and aerospace and other industris. Because of increasing composites utilization in industries, it is necessary to stabilize and set standards of machining parameters. Drilling is the main machining operation in producing process for assembled the composite work piece. So the quality of drilling hole should be considered to avoid snapping mechanical structure. Tool geometry is one of the most important factors in the drilling process. If it is neglected, the thrust forced increase, and it causes damage around the hole such as delamination, large entrance and exit burr, and induced cracks. The most damaging in drilling FRP is delamination of the composites lamina that occurs when drill bit is entered and exited. In the other hand, this study used ANSYS finite element software to determine the value of stress in composite plate and use to analyze for designing the jig & fixture in this drilling process. In conclusion, with comparing delamination, the best geometry tool introduced for the lowest amount of damage.

Abstract: An ultrafine grained 304L stainless steel with average grain size of 650±100 nm was produced by a combination of cold rolling and annealing. Wear behavior of the steel was examined by dry sliding wear tests under different loads. Different microstructural characterizations were conducted on the ultrafine grained structure after thermomechanical processing and wear tests. The results demonstrated that the steel had yield strength of 720 MPa and total elongation of 47%, which is almost twice higher than typical coarse grained strength. Also, wear tests results showed a good linear relation between the cumulative wear loss and distance in each normal load. Wear rate was about 0.024, 0.043 and 0.093 mg/m for normal loads of 10, 20 and 30N, respectively. Wear mechanism was also recognized as delamination (in the early stage) and mixture of delamination and abrasion in higher distances.

Abstract: This paper presents a study on the influence of cutting parameters (Cutting speed and Feed rate) on drilling multi walled carbon nanotubes (MWCNTs) filled epoxy / glass fabric hybrid polymeric nanocomposite. For comparison neat epoxy / glass fabric polymeric composite was also fabricated. Drilling tests were carried out on these materials with HSS twist drill of diameter 6mm. Optimal cutting conditions were found using grey relational analysis by simultaneously considering the surface delaminations of the drilled holes at the entrance and exit sides. Surface delaminations of the drilled holes were quantified in terms of delamination factor. From the mean grey relational grades, it is observed that the multi walled carbon nanotubes (MWCNTs) has significant effect in improving the drilled hole quality. Mean grey relational grades of MWCNTs filled epoxy composite was found to be better than that of neat epoxy composite.

Abstract: The growing demand for light weight materials for the application in the aircraft industries, aerospace industries, marine, sports and recreation industries has attracted the usage of fiber reinforced materials especially GFRP composites. Usage of these kind of materials are exponentially increasing because of its specific engineering characteristics like high strength to weight ratio. Drilling of these materials has been always a challenge because of its heterogeneous nature. Better hole quality is required for these materials for the assembly into components. In this work delamination analysis was attempted using digital image processing, experiments are carried out for 27 holes using full factorial design and it was observed that scanned images obtained using a flat bed scanner (HP, 1300 DPI) used for digital image processing, gives better visualization for delamination. The feed rate is the most influencing parameter out of the three process input parameters considered.

Abstract: Drilling is frequently used in machining of carbon fiber reinforced materials. Twist drill is mostly used in drilling composite materials and some other drills with special drill bits are also needed. Drilling induced delamination is considered one of the most serious problems during machining while drilling force plays a decisive role in delamination. This paper presents the analysis of critical thrust force with special drill bit theoretically. The method of simulation to study the critical thrust force is also introduced. In addition, effect of cutting parameters on delamination by comparing experimental results and mathematical model of twist drill is studied.