柴油机活塞环磨损的原因及预防

对柴油机活塞环磨损的形式及原因进行了分析,并提出了材料的合理选型、进行表面处理和结构形状的改进等减少磨损的措施。

Advanced simulation of die wear caused by wire vibrations during wire-drawing process

An advanced simulation that considers the effect of wire vibrations was proposed for predicting accurately wear profiles of a die used in a wire-drawing process.The effect of wire vibrations,the changes in the wear profiles,and the generation of ringing during die approach were investigated by this simulation.Wire vibrations occurring between the die and the drum are governed by a partial differential equation called the wave equation,which is a function of the wire length,tension,density,and initial wire velocity.The wire-drawing process was simulated by the commercial code Abaqus FEA,and the die wear profiles were predicted by Archard’s wear model.The predicted profiles were compared with measured profiles of a worn drawing die after producing 5 t of AISI 1010 wire;the die was made of tungsten carbide with a Brinell hardness of HB 682.The profiles predicted by considering the effect of wire vibrations are in good agreement with the experimental data,indicating that the advanced simulation can be used to accurately predict the die wear profiles when ringing is observed during die approach.

A prediction method of rail grinding profile using non-uniform rational B-spline curves and Kriging model

Non-uniform rational B-spline(NURBS)curves are combined with the Kriging model to present a prediction method of the rail grinding profile for a grinding train.As a worn rail profile is a free-form curve,the parameterized model of a rail profile is constructed by using the cubic NURBS curve.Taking the removed area of the rail profile cross-section by grinding as the calculation index of the grinding amount,the grinding amount calculation model of a grinding wheel is established based on the area integral formula of the cubic NURBS curve.To predict the grinding amount of a grinding wheel in different modes,a Kriging model of the grinding amount is constructed,taking the travel speed of a grinding train,the grinding angle and grinding pressure of a grinding wheel as the variables,and considering the grinding amount of a grinding wheel as the response.On this basis,the prediction method of the rail grinding profile is presented based on the order-forming mechanisms.The effectiveness of this method is verified based on a practical application.

Chest injury in victims of Bam earthquake

Objective： To analyze the data of trauma patients with thoracic injury in the earthquake of Bam admitted to hospitals of Tehran University of Medical Science （ TUMS ） for better understanding the type and consequence of thoracic injuries in a major earthquake. Methods： After Barn earthquake registering 6.5 on the Richter scale, 526 trauma patients were admitted to hospitals of TUMS. Among them, 53 patients sustained thoracic injury. Results： This group was composed of 21 females （39.6%） and 32 males （60.4%）. Fifteen patients （28.3%） had isolated chest injuries. Rib fracture （36.4 % ） was the most common injury in our patients and haemo/pneumothorax （ 25.5 % ） followed. Superficial injury was the most common accompanying injury. Multiple- trauma patients with chest injury had higher injury severity score （ISS） versus patients with isolated chest injury （P =0.003）. Conclusions： Chest wall injuries and haemo/ pneumothorax comprise a considerable number of injuries in survival victims of earthquakes. Consequently, the majority of these patients can be treated with observation or tube thoracostomy. We should train and equip the health workers and members of rescue teams to treat and manage these patients in the field.

aseudoarthrosis of medial tibial plateau fracture role of alignment procedure

Nonunion in tibial plateau fractures is very rare. Limited literature is available on Pubmed search on intraarticular tibial nonunion. Most of the cases reported have been following failed surgical treatment and none was neglected fractures. Three patients of isolated and neglected medial fibial plateau nonunion with almost similar demo- graphic profile are reported in this paper. All the three pa- tients were managed by minimally invasive compressionfixation using lag screws supplemented with limb realign- ment procedure of high tibial osteotomy. We discussed the injury mechanism, management and rehabilitation in such cases and reviewed the available literature regarding such a presentation.

Investigation of Non-Axisymmetric Endwall Contouring in a Compressor Cascade

The current paper presents experimental and computational results to assess the effectiveness of non-axisymmetric endwall contouring in a compressor linear cascade. The endwaU was designed by an endwall design optimi- zation platform at 0° incidence （design condition）. The optimization method is based on a genetic algorithm. The design objective was to minimize the total pressure losses. The experiments were carried out in a compressor cascade at a low-speed test facility with a Mach number of 0.15. Four nominal inlet flow angles were chosen to test the performance of non-axisymmetric Contoured Endwall （CEW）. A five-hole pressure probe with a head diameter of 2 mm was used to traverse the downstream flow fields of the flat-endwall （FEW） and CEW cascades. Both the measured and predicted results indicated that the implementation of CEW results in smaller comer stall, and reduction of total pressure losses. The CEW gets 15.6% total pressure loss coefficient reduction at design condition, and 22.6% at off-design condition （＋7° incidence）. And the mechanism of the improvement of CEW based on both measured and calculated results is that the adverse pressure gradient （APG） has been reduced through the groove configuration near the leading edge （LE） of the suction surface （SS）.