Adoption of internet banking : an empirical study in Hong Kong

2006-2007 > Academic research: refereed > Publication in refereed journalAccepted ManuscriptPublishe

Influences of residual stresses and initial distortion on springback prediction of 7B04-T651 aluminium plates in creep-age forming

Springback behaviour of surface-machined 7B04-T651 aluminium plates of 3–8 mm thicknesses, creep-age formed under a single curvature bending radius of 1200 mm, has been experimentally investigated. The surface residual stress levels of the plates have been measured and the typical residual stress distribution and values in 7000-series aluminium alloys have been reviewed and analysed. Finite element models have been developed to simulate creep-age forming (CAF) processes and predict the amount of springback in the physical CAF test. Machining-induced residual stresses and distortion have been considered in the finite element models. This paper presents a first attempt to study the effect of machining-induced residual stresses on the errors of springback prediction in CAF of 7000-series aluminium alloy panel components. It has been found that the effect of machining-induced residual stresses on the accuracy of springback prediction is related to the initial loading stress levels in CAF. In addition, when the initial distortion conforms to the loading curvature, an opposing effect on the material’s deformation is observed

Constitutive modelling of creep-ageing behaviour of peak-aged aluminium alloy 7050

The creep-ageing behaviour of a peak-aged aluminium alloy 7050 was investigated under different stress levels at 174 ∘C for up to 8 h. Interrupted creep tests and tensile tests were performed to investigate the influences of creep-ageing time and applied stress on yield strength. The mechanical testing results indicate that the material exhibits an over-ageing behaviour which increases with the applied stress level during creep-ageing. As creep-ageing time approaches 8 h, the material's yield strength under different stress levels gradually converge, which suggests that the difference in mechanical properties under different stress conditions can be minimised. This feature can be advantageous in creep-age forming to the formed components such that uniformed mechanical properties across part area can be achieved. A set of constitutive equations was calibrated using the mechanical test results and the alloy-specific material constants were obtained. A good agreement is observed between the experimental and calibrated results

Material modelling for creep-age forming of aluminium alloy 7B04

This paper presents a study on the creep-ageing behaviour of a peak-aged aluminium alloy 7B04 under different tensile loads at 115oC and subsequently modelling it for creep-age forming (CAF) applications. Mechanical properties and microstructural evolutions of creep-aged specimens were investigated. The material was modelled using a set of unified constitutive equations, which not only captures the material's creep deformation but also takes into account yield strength contributions from solid solution hardening, age hardening and dislocation hardening during creep-ageing. A possible application of the present work is demonstrated by implementing the determined material model into a commercial finite element analysis solver via a user-defined subroutine for springback prediction of creep-age formed plates. A good agreement is observed between the simulated springback values and experimental results. This material model now enables further investigations of 7B04 under various CAF scenarios to be conducted inexpensively via computational modelling

Material modelling and its application to creep-age forming of aluminium alloy 7B04

Creep-ageing behaviour of aluminium alloy 7B04-T651 at 115 °C under a range of tensile stress levels has been experimentally investigated and numerically modelled for creep-age forming (CAF) applications. Creep strain, yield strength evolution and precipitate growth of creep-aged specimens were investigated. The alloy was modelled using a set of unified constitutive equations, which captures its creep deformation and takes into account yield strength contributions from three creep-age hardening mechanisms. Applications of the present work are demonstrated by implementing the determined material model into a commercial finite element analysis solver to analyse CAF operations carried out in a novel flexible CAF tool. Stress relaxation, yield strength, precipitate size and springback were predicted for the creep-age formed plates. The predicted springback were further quantified and compared with experimental measurements and a good agreement of 2.5% deviation was achieved. This material model now enables further investigations of 7B04 under various CAF scenarios to be conducted inexpensively via computational modelling

Creep-age forming AA2219 plates with different stiffener designs and pre-form age conditions: Experimental and finite element studies

AbstractCreep-age forming (CAF) is one of the relatively new forming techniques that has been proven viable for the production of extra-large integral airframe structures. However, experimental studies on forming stiffened structures under creep-ageing conditions remain scarce. In this work, 200mm×48mm integrally stiffened plates of aluminium alloy 2219 have been formed on an end clamp device that has a bending radius of 156mm and creep-aged at 175°C for 18h. Three different stiffener designs, namely the beam stiffened, waffle and isogrid plates, are tested alongside the flat plates. Utilisation of PTFE pocket fillers and intermediate sheets to reinforce and protect stiffeners during forming operation is found effective as demonstrated by the defect-free formed parts with smooth curvature. Springback of the plates ranged from 12.2 to 15.7% in the experimental studies for different stiffener designs. Using the CAF material constants determined for this alloy, corresponding finite element models have been developed and experimentally validated using the measured profiles of the creep-age formed plates. Up to 6.3% difference in springback is observed when forming workpieces with different pre-form age condition alone

A review of clinicopathologic features of pheochromocytomas in Hong Kong Chinese

Twenty-two Chinese patients with pheochromocytomas incuding 18 surgical and four autopsy cases were reported. The incidence at autopsy was 0.048%. The tumours were most common in the sixth and the fourth decades in males and females respectively. There was no sex predilection. The incidence of bilaterality was 4.5% and the tumours were more common on the right side. 9.1% of the the tumours were malignant and they were larger than their benign counterparts. Solid and diffuse pattern and mixed pattern were the most common histologic patterns. Minor histological features included hyaline globules (64%) nuclear pseudo-inclusions (55%) lipid degeneration (4.5%) and peri-adrenal brown fat (18%). All of them were strongly positive for the three pan-neuroendocrine markers (neuron-specific enolase synaptophysin and chromogranin) confirming the usefulness of these markers in diagnosing pheochromocytoma.link_to_subscribed_fulltex

Giant adrenal lipoma: A report of two cases and review of the literature

Lipoma of the adrenal gland is extremely rare. We report two cases of adrenal lipomas, one in a 64-year-old female and the other a 78-year-old male. The sizes of these tumours (4.5 cm and 8 cm) were larger than those reported in the literature. Both cases were found incidentally, one at autopsy and the other during ultrasonographic examination for unrelated condition. The histogenesis, clinicopathological features, differential diagnosis and management of these cases are discussed.link_to_subscribed_fulltex

Bladder tumours in Chinese: A 6 year study

Specimens from 334 Chinese patients who underwent surgical treatment for bladder tumours over a 6 year period were studied retrospectively. Transitional cell carcinoma (TCC) accounted for 91.3% of all the bladder tumours. The male to female ratio was 3:1 and the mean age was 69 years. Papillary TCC, which represented 67.5% of all TCC, were more often of a lower grade compared to non-papillary tumours. The staging of tumours was done for the 102 cystectomy specimens with TCC only. Among these, 28% were superficial while 72% were muscle-invasive and the papillary TCC usually presented at an earlier stage. Infiltration into the prostate gland was identified in 11% of male patients while coexisting adenocarcinoma of the prostate was observed in another 4.2%. Other types of carcinoma were uncommon. Squamous cell carcinoma, adenocarcinoma and small cell carcinoma accounted for 2.7, 1.8 and 0.6% of all bladder tumours, respectively. A rare case of sarcomatoid carcinoma was also found, but no true sarcoma was documented in this series. Benign lesions included five inverted papillomas, three nephrogenic adenomas, two paragangliomas and one haemangioma.link_to_subscribed_fulltex