3D Finite Element Model on Drilling of CFRP with Numerical Optimization and Experimental Validation

When drilling Carbon Fibre-Reinforced Plastic (CFRP) materials, achieving acceptable hole quality is challenging while balancing productivity and tool wear. Numerical models are important tools for the optimization of drilling CFRP materials in terms of material removal rate and hole quality. In this research, a macro-Finite Element (FE) model was developed to accurately predict the effect of drill tip geometry on hole entry and exit quality. The macro-mechanical material model was developed treating the Fiber-Reinforced Plastic (FRP) as an Equivalent Homogeneous Material (EHM). To reduce computational time, a numerical analysis was performed to investigate the influence of mass scaling, bulk viscosity, friction, strain rate strengthening, and cohesive surface modelling. A consideration must be made to minimize the dynamic effects in the FE prediction. The experimental work was carried out to investigate the effect of drill tip geometry on drilling forces and hole quality and to validate the FE results. The geometry of the drills used were either double-point angle or a “candle-stick” profile. The 3D drilling model accurately predicts the thrust force and hole quality generated by the two different drills. The results highlight the improvement in predicted results with the inclusion of cohesive surface modelling. The force signature profiles between the simulated and experimental results were similar. Furthermore, the difference between the predicted thrust force and those measured were less than 9%. When drilling with a double-angle drill tip, the inter-ply damage was reduced. This trend was observed in FE prediction.

Analytical bond behavior of cold drawn SMA crimped fibers considering embedded length and fiber wave depth

The NiTi SMA fibers were cold drawn to introduce prestrain, and then, they were made to crimped fibers with various wave depths. The recovery stress was measured, which was useful for closing the cracks in fiber-reinforced concrete. The pullout behaviors were also examined considering the existing recovery stress, and it is found that the recovery stress did not influence so much on the pullout behavior. According to the pullout results, a parametric study used a finite element analyzing (FEA) model to quantify the cohesive surface model’s parameters and the value of the friction coefficient. Then, the developed model is used to investigate the crimped fiber’s pullout behavior with various embedded lengths and wave depths. When the fiber in the elastic range, the peak stresses significantly raise due to increasing embedded waves; they show a linear relationship. After the yield of the SMA fiber, the peak stresses are also a function of embedded waves; however, the increasing trend is slow down. Concerning the cost, the even distribution of the fiber, and for guaranteeing the fiber experiences the pulling out, it is recommended that the embedded lengths and corresponding wave depths should be designed to avoid the yield.

Experimental and numerical investigation of interface damage in composite L-angle sections under four-point bending

Curved laminates in aero-structures, such as the L-angle sections where webs and flanges meet, are prone to delamination due to high interlaminar stresses in these regions. Some efforts to investigate delamination in these structures can be found in the literature but commonly structures are limited to unidirectional layups or modelling approaches are constrained to the cohesive element based methods. In this work, multi-directional L-angle laminates were manufactured using unidirectional prepregs and tested under four-point bending load conditions to examine the interface damage. Acoustic emission technique was used to assist the capture of damage initiation and propagation. Three interface modelling strategies for predicting delamination, namely cohesive element, cohesive surface and perfectly bonded interface were used in the numerical study. The interface damage behaviour was successfully predicted by the simulation methods and differences among the strategies were compared.

USING SIMULATION TO STUDY CUTTING FORCE IN BIOPSY NEEDLE INSERTION WITH BI-DIRECTIONAL ROTATION

The rotational motion has been utilized in several medical needle technologies to enhance the capability of cutting tissue. The needle rotation helps significantly reduce the tissue cutting force, which improves procedure outcome and pain. However, the needle rotation can also incur tissue winding that intensifies tissue damage, which results in complications of bleeding and hematoma. Some histological observations showed that bidirectional needle rotation could reduce the tissue damage caused by tissue winding. In this study, we established a cohesive surface based finite element model to evaluate the cutting force in needle insertion with unidirectional and bidirectional rotation. The simulation results suggested that the frequency of switching direction of needle rotation insignificantly influences the cutting force. The Latin Hypercube method was used to generate a response surface of cutting force and locate the minimum at the insertion speed of 1[Formula: see text]mm/s combined with the slice/push ratio of 1.9. In clinical use, we suggested that the needle speeds can be first selected to optimize the cutting force according to the type of target tissue. If the desired needle rotation is high, a proper switching frequency can be applied to reduce the tissue winding damage without increasing the cutting force.

Reproducibility of pop-in using heterogeneous welded joint specimen and cohesive surface model

When a pop-in as a phenomenon of initiation, propagation, and arrest of a brittle crack occurs in the fracture toughness test, the fracture toughness may be evaluated extremely low. In order to identify the cause of pop-in occurrence, an objective of this study was to demonstrate pop-ins in the three-point bend fracture toughness tests. It was possible to reproduce pop-ins at LBZ zone by preparing the specimens containing heterogeneous weld metals and considering the temperature dependency of the toughness in each welding material. Furthermore, the pop-in occurrence could be simulated by finite element analysis using a cohesive surface.