Sharif Digital Repository

The fiber-reinforced composite materials possess advantage for structural purpose in various industries. Delamination is recognized as one of the major causes of damage during drilling of fiber reinforced composites, which not only reduces the structural integrity, but also has the potential for long-term performance deterioration. It is difficult to produce precise quality holes with high efficiency by conventional drilling method. Drilling is frequently applied in production cycle while the anisotropy and nonhomogeneity of composite materials affect the chip deformation and machining behavior during drilling. In this thesis, a new non-traditional drilling technology is presented for solve... 

In this research, delamination in compound laminated materials under the I mode loading is studied. In this way, a Double Cantilever Beam is investigated, which is the only experiment to study delamination in standard compound laminated materials. At first, a survey and comprehension of the failure of these materials is performed and the major mode of failure, which is named Delamination Mode is understood. Next, a survey on the possible methods of investigating the delamination phenomena is presented. In the next chapter, possible numerical methods are analysed, and the better performance of Cohesive Zone Model and Virtual Crack Closure Technique is studied. In this research, using the... 

Delamination is a major problem in drilling of fiber-reinforced composite materials. Thrust force is an important factor leading to propagation of delamination during drilling process. One of effective methods to reduce machining forces is application of ultrasonic vibrations. In this study ultrasonic assisted drilling is applied to reduce thrust force in drilling of GFRP laminates. In order to conduct experiments a setup is designed and fabricated to apply both vibrations and rotation to drill bits. Using Taguchi method, a set of experiments is conducted with feed rate, spindle speed, point angle and ultrasonic vibration amplitude as control factors. The results show that applying... 

Composite structures are subjected to different kinds of loadings in different workspaces, and sometimes these load conditions can damage them. Delamination is a common damage in composites. In this research, the delamination effect on modal behavior of a laminated composite plate is studied. To investigate this effect, the frequency response method is used and piezoelectric patches are used as a sensor and an actuator for extracting the frequency response. The aim of this project is to investigte presence and severity of the delamination. To survey the frequency response method, an intact and some damaged plates with one sensor and actuator are modeled with abaqus software and frequency... 

In the present work, the beginning and progressive growth of delamination in laminated composites plates has been studied. Interlaminar stresses at free edge of laminate may give rise to edge delamination and result in failure of laminate. So we need to determine the exact interlaminar stresses to predict the failure of laminated composites. A computer code based on layerwise theory that can obtain the exact interlaminar stresses been developed. Comparison between the present study and finite element software result showed the good agreement.A fracture mechanics approach is used to analysis delamination propagation between layers of composites laminate. In this approach damage propagation... 

This study presents delamination in fiber-reinforced composite laminates by using multiscale modeling. The meso modeling is used to derive the relationship between microcrack density and damage parameters. Next the selected failure model is applied to analyze the macroscale modeling. The progress of failure terms and the reduction of fiber and matrix properties implemented into ABAQUS/Standard, which enables an individual to create a new material behavior through the user subroutine UMAT. In the following, the contours associated with each of the damage parameters are obtained in each of the damage mode. Then for a specific material, the relationship between microcrack density and damage... 

This thesis aims to develop a numerically efficient nonlinear layer-wise shell element formulation for delamination analysis of laminated composite shell structures. The element, in a mesoscale scheme, is formulated based on a zig-zag theory and features three translational degrees of freedom for each node on the mid-surface of the shell in addition with two rotational degrees of freedom for each layer. In this way, the displacement field is formulated via adapting the Mindlin-Reissner theory in each layer and an ordered second-order algorithm for finite rotations. To verify the proposed formulation, many popular benchmark problems for geometric nonlinear analysis of shell problems are... 

This paper presents, various parameters of the composite patch for repairing and reinforcement the damaged composite pipe have been investigated. There are various parameters of the composite patch such as Laminate orientation, length, width, material and thickness of the patch. by changing these parameters in each analysis and comparing the results, the optimal patch for the damaged pipe is determined