Search

Many carbon fibre reinforced polymer composite parts need to be edged trimmed before use to ensure both geometry and mechanical performance of the part edge matches the design intent. Measurement and control of machining induced surface damage of composite material is key to ensuring the part retains its strength and fatigue properties. Typically, the overall surface roughness of the machined face is taken to be an indicator of the amount of damage to the surface, and it is important that the measurement and prediction of surface roughness is completed reliably. It is known that the surface damage is heavily dependent on the fibre orientation of the composite and cutting tool edge condition. This research has developed a new ply-by-ply surface roughness measurement methods using optical focus variation surface analysis and image segmentation for calculating areal surface roughness parameters of a machined carbon fibre composite laminate. Machining experiments have been completed using a polycrystalline diamond edge trimming tool at increasing levels of cutting edge radius. Optical surface measurement and µ-CT scanning have been used to assess machining induced surface and sub-surface defects on individual fibre orientations. Statistical analysis has been used to assess the significance of machining parameters on Sa (arithmetic mean height of area) and Sv (areal magnitude of maximum valley depth) areal roughness parameters, on both overall roughness and ply-by-ply fibre orientations. Empirical models have been developed to predict surface roughness parameters using statistical methods. It has been shown that cutting edge degradation, fibre orientation and feed rate will significantly affect the cutting mechanism, machining induced surface defects and surface roughness parameters.

Nowadays, the development of robust finite element models is vital to research cost-effectively the optimal cutting parameters of a composite machining process. However, various factors, such as the high computational cost or the complicated nature of the interaction between the workpiece and the cutting tool significantly hinder the modelling of these types of processes. For these reasons, the numerical study of common machining operations, especially in composite machining, is still minimal. This paper presents a novel approach comprising a mixed multidirectional composite damage mode with composite edge trimming operation. An ingenious finite element framework which infer the cutting edge tool wear assessing the incremental change of the machining forces is developed. This information is essential to replace tool inserts before the tool wear could cause severe damage in the machined parts. Two unidirectional carbon fibre specimens with fibre orientations of 45° and 90° manufactured by pre-preg layup and cured in an autoclave were tested. Excellent machining force predictions were obtained with errors below 10% from the experimental trials. A consistent 2D FE composite damage model previously performed in composite machining was implemented to mimic the material failure during the machining process. The simulation of the spring back effect was shown to notably increase the accuracy of the numerical predictions in comparison to similar investigations. Global cutting forces simulated were analysed together with the cutting tool tooth forces to extract interesting conclusions regarding the forces received by the spindle axis and the cutting tool tooth, respectively. In general terms, vertical and normal forces steadily increase with tool wear, while tangential to the cutting tool, tooth and horizontal machining forces do not undergo a notable variation.

Characterization of the damage induced by machining of fibre-reinforced composites is usually performed by measuring surface roughness. Contact-based surface profilometers are the most used equipment in industry; however, it has been found that there are performance limitations which may result when used to measure machined heterogeneous composite surfaces. In this research, surface roughness is characterised using a commercial non-contact optical method, and compared with a conventional stylus profilometer. Unidirectional and multidirectional carbon fibre laminates were edge trimmed and slot milled. The variation in surface roughness was compared using different tool types, fibre orientations and cutting parameters. Surface damage and cutting mechanisms were assessed by using scanning electron microscope images, and the suitability of roughness parameters were also analysed including: Sa, Skewness and Kurtosis. Using the optical system allowed accurate roughness calculation of individual plies on a multidirectional laminate with different fibre orientations. The research has also shown that the optical system, including the use of areal roughness parameters, can increase the accuracy of roughness measurement for machined fibrous composite surfaces and is less sensitive to measurement position than the stylus.

Better control of fibre composites machining requires reliable surface roughness and damage characterisation measurements. The\ud performance and tool wear rate of three different state of the art CVD and PCD cutting tools manufactured for carbon fibre\ud machining were compared in wet and dry conditions. Machined surfaces were characterised by areal surface roughness\ud parameters using a novel focus variation optical system. The tool wear and cutting forces were recorded up to 50 linear meters of\ud machining or until tool failure. Results showed that wet machining conditions reduced tool failure; and that the CVD tool in wet\ud conditions machined the greatest distance of 26m before reaching an average roughness limit of 3μm. The tool type was found to\ud be the most significant parameter on the surface quality. The optical system was found to be a useful tool for measuring\ud roughness of individual plies and characterising machining induced surface damage.

BACKGROUND Most recent trials in human leukocyte antigen (HLA)-identical living donor (LD) renal transplantation have used immunosuppressive regimens with no induction therapy, corticosteroid-free long-term treatment, and calcineurin inhibitor minimization. PATIENTS AND METHODS Seven HLA-identical LD recipients were prospectively enrolled. Immunosuppression included induction therapy with antithymocyte globulins for 10 days and long-term monotherapy with mycophenolate mofetil (2 g/day) in six cases and sirolimus (target trough levels: 6-10 ng/mL) in the last case. A single preoperative steroid bolus was administered. RESULTS After a median follow-up time of 26 months (range: 5-50 months), patient and graft survival was 100%. Only one patient experienced borderline lesions at 3 months and received steroids for a 5-month period. All patients had a protocol biopsy at 3 months, and four had a second at 12 months. Acute cellular rejection was not observed. Median serum creatinine at 3 months, 12 months, and last follow-up were 103.1, 107.1, and 106.1 [mu]mol/L, respectively. For four patients, measured glomerular filtration rate was evaluated at 3 months, and the mean value was 71.2 mL/min/1.73 m2. CONCLUSIONS Induction therapy with antithymocyte globulins followed by mycophenolate mofetil or sirolimus monotherapy provides excellent patient and graft survival, excellent renal function, and no acute rejection episodes in HLA-identical LD renal transplant recipients.

Since the CMP process depends on chemical and mechanical effects, the interaction with the physical and chemical properties of the GST alloy play very important roles during the CMP process. In this paper, the impact of the CMP process on a soft GST alloy will be discussed. In addition, the paper addresses how major chemical properties of the GST alloy affect the GST CMP process. For example, in order to remove the three different elements of GST material during the CMP process, it is critical to understand how the alloy's chemical behavior changes when interacting with the CMP slurries. A fully characterized GST CMP baseline process, including its process and defect results, will be presented. The methods used to optimize the CMP process and reduce post-CMP defects will also be discussed.