Papers by Author: Qing Long An

Abstract: High strength carbon fiber reinforced polymers (CFRP) with unidirectional laminate structure have gradually developed into major materials in load-bearing aerospace components, and the cutting demand of CFRP is increasing. In this work, orthogonal cutting tests were conducted on T700 high-strength CFRP laminates to get the mechanistic force model of special cutting tools. Also cutting force coefficients were obtained when cutting T700 high-strength CFRP laminates under different fiber orientations. Experimental results showed that the lowest cutting force was obtained when fiber orientation was between 120° and 150°.

Abstract: Machined surface quality is the deciding factor when evaluating the machinability of CFRP. This present work concerns the influence of fiber orientation on the machined surface quality of the machined surface in terms of surface morphology and surface roughness during milling of unidirectional T800/X850 CFRP laminates. Four group milling tests are conducted under the fiber orientation angle of 0°, 45°, 90° and 135°, respectively. For the fiber orientation angle of 0°, the machined defects are mainly fiber pull-out and fiber brittle fracture owing to interfacial debonding between the fibers and matrix resin. For the fiber orientation angle of 45°, the machined defects are mainly resin cavities and the surface morphology is rough and presents wavy fractures. For the fiber orientation angle of 90°, smooth or neat surface is observed except for the surface as the cutting tool cutting in the workpiece on which severe cracks are observed. For the fiber orientation angle of 135°, the surface is smooth with less fibers pull-out. Evaluation profile and surface roughness of the machined surfaces were measured as well. Dramatically fluctuate of the evaluation profile is observed for the fiber orientation angle of 45° with a high surface roughness Ra. Verification tests were also conducted on the multidirectional CFRP (cross-ply) laminates. It is indicated that the presence of the fiber orientation angle of 45° is the main factor leading to the decline of the machined surface quality.

Abstract: Carbon fiber reinforced polymers (CFRP) are increasingly used in aerospace and other industries, due to its high specific strength and stiffness. Machining operations are involved between forming fabrication and assembling as a fining process, during which defects like delamination, burrs and splintering are the main cause of substandard products. This is because that CFRP is a typical difficult to machine material with distinct anisotropy and heterogeneity. Thus machinability of CFRP material under different fiber orientations is a main issue. This paper intensively investigated on cutting forces and temperatures when orthogonal cutting of 0° T700/LT03A CFRP uniform laminates, with fiber orientation from 0°to 180°. Material removal mechanisms and carbon fiber fraction modes under various fiber orientations were discussed. The results showed that fiber orientation of 90°is the worst scenario of cutting, under which condition the force and temperature of the highest level, while that of 150°indicates the other. The results of cutting temperature indicated that it is mainly from the friction heat in the zone III generated by the thrust force.

Abstract: Lots of hole machining in CFRP(carbon fiber reinforced plastics) are conducted in the astronautic fields, especially a large size hole machining. The purpose of this article is to investigate the optimal cutting parameters and allowance distribution in CFRP 18/32inch hole machining by thoroughly considering the cutting forces and burr length. All tests were run without coolant using different drills, expanding drills and reamers. The damage generated and the cutting forces produced in CFRP composites cutting were observed. Therefore, the optimal allowance distribution in CFRP large size hole machining was obtained, providing compound tools design with theoretical direction.

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.

Abstract: Studying the dynamic properties of a material are an important method to understand the dynamic processes and deformation mechanism of material at different working conditions, particularly at high strain rate. The constitutive equation of a material has the highest significance to represent the mechanical properties, and is the principal research basis for the numerical simulation. In this paper, an important titanium alloy TC11 was studied through the quasi-static tensile test and the split Hopkinson pressure bar (SHPB) tests. Dynamic compressive behavior of TC11 alloy was discussed. Moreover, this paper gave the constitutive model of TC11 alloy and established the Johnson-Cook (J-C) constitutive equation.

Abstract: This paper investigates the surface integrity of premium thread gauge material 9Mn2V in reciprocating surface grinding using SG abrasive, which includes metallographic structure for grinding crack, specific grinding energy and surface residual stress. The specific grinding energy and the surface residual stress can be reduced after the workpiece gets tempered, so small grinding depth can lead to the generation of cracks when the workpiece is not tempered. Otherwise, the depth of heat affected zone increases with the increase of grinding depth, but not increases proportionally. After 9Mn2V is tempered, the occurrence of grinding burn and grinding cracks can be improved.

Abstract: Carbon fiber reinforced plastics (CFRP) has increasing applications in aerospace and other fields, due to low density, high strength, high stiffness, great resistance to corrosion, etc. Although, delamination damages in drilling holes for assembly influence the final characteristics of CFRP components. This paper presents an experimental investigation to analyze delamination damage, in which acoustic emission and thrust force are monitored during drilling CFRP laminates to clarify the relationship between AE signals and delamination damages. The results show that delamination damage has close correlation with thrust force and acoustic emission energy. AE root mean square (rms) is recommended to be selected as AE signal parameter. Abrupt peak feature of AE rms can be used as a dependable trigger for delamination monitoring. The number of abrupt pulses of AE rms can be counted online to predict the degree of delamination damages, based on which delaminations can be monitored and controlled online.

Abstract: Ultra-high-strength steel 30Cr3SiNiMoVA (30Cr3) which has excellent mechanical properties is usually used to manufacture the key parts in aviation industry. Precision hard milling is an efficiency way to machine 30Cr3 instead of grinding. Rounded cutting edge radius has important influence on the machining process due to small depth of cut. In order to better understanding the influence of rounded cutting edge radius, cutting forces, cutting temperature, critical depth of cut, etc., is analyzed by using finite element method (FEM). The results show that cutting forces in the y direction are more sensitively to the rounded cutting edge radii. Ploughing effect is also observed at the end of the climb milling process and it has significant influence on the quality of the machined surface. Simulation reveals that the increment of rounded cutting edge radius can lead to the increment of critical depth of cut correspondingly and the proportionality factor is about 14%.

Abstract: High-strength carbon fiber reinforced plastic (CFRP) T800S/250F is used as the large commercial aircraft material for manufacturing the main load-bearing structural components. Drilling is the mostly used in final machining process of CFRP laminates, while the delamination and burrs occur frequently at the drill exit in the CFRP laminate. In this paper, the machinability of T800S/250F was investigated in term of drilling force and hole quality by using a twist drill and a dagger drill. The experimental results indicated that high spindle speed and low feed rate favor the reduction of thrust force for both drill bits. High spindle speed is a preference to gain the good hole quality at drill exit especially for the dagger drill, which also shows excellent drilling performance than the twist drill and was more suitable for drilling of T800S/250F CFRP laminate.