Qingliang Wang

Preparation and properties of a new cutting pick of coal shearers

Abstract Reliability and wear resistance of cutting picks play a significant role in coal mine exploitation with coal shearers. Tool bit separation, blade breaking, severe erosion of the cutting body and fatigue fractures are the main reasons for failure of cutting picks. We carried out carburization on a 30CrMnMo alloy to synthesize a new cutting pick material with improved mechanical properties and high wear resistance. The results indicated that carburization can effectively strengthen the surface of the 30CrMnMo alloy by forming a thick carburized layer and thus significantly improve the surface hardness and wear resistance. In addition, the excellent toughness of 30CrMnMo alloy as a substrate of cutting picks can prevent brittle ruptures and fatigue fractures under high impact stress conditions. The significant decrease in both frictional coefficient and rate of erosion of this carburized 30CrMnMo alloy suggests that this alloy is a potential material for cutting picks of coal shearers after rational carburization.

Research on torsional friction behavior and fluid load support of PVA/HA composite hydrogel

Hydrogels have been extensively studied for use as synthetic articular cartilage. This study aimed to investigate (1) the torsional friction contact state and the transformation mechanism of PVA/HA composite hydrogel against CoCrMo femoral head and (2) effects of load and torsional angle on torsional friction behavior. The finite element method was used to study fluid load support of PVA/HA composite hydrogel. Results show fluid loss increases gradually of PVA/HA composite hydrogel with torsional friction time, leading to fluid load support decreases. The contact state changes from full slip state to stick-slip mixed state. As the load increases, friction coefficient and adhesion zone increase gradually. As the torsional angle increases, friction coefficient and slip trend of the contact interface increase, resulting in the increase of the slip zone and the reduction of the adhesion zone. Fluid loss increases of PVA/HA composite hydrogel as the load and the torsional angle increase, which causes the decrease of fluid load support and the increase of friction coefficient.

Contact damage failure analyses of fretting wear behavior of the metal stem titanium alloy–bone cement interface

Although cemented titanium alloy is not favored currently in the Western world for its poor clinical and radiography outcomes, its lower modulus of elasticity and good biocompatibility are instrumental for its ability supporting and transforming physical load, and it is more suitable for usage in Chinese and Japanese populations due to their lower body weights and unique femoral characteristics. Through various friction tests of different cycles, loads and conditions and by examining fretting hysteresis loops, fatigue process curves and wear surfaces, the current study investigated fretting wear characteristics and wear mechanism of titanium alloy stem-bone cement interface. It was found that the combination of loads and displacement affected the wear quantity. Friction coefficient, which was in an inverse relationship to load under the same amplitude, was proportional to amplitudes under the same load. Additionally, calf serum was found to both lubricate and erode the wear interface. Moreover, cement fatigue contact areas appeared black/oxidative in dry and gruel in 25% calf serum. Fatigue scratches were detected within contact areas, and wear scars were found on cement and titanium surfaces, which were concave-shaped and ring concave/ convex-shaped, respectively. The coupling of thermoplastic effect and minimal torque damage has been proposed to be the major reason of contact damage. These data will be important for further studies analyzing metal-cement interface failure performance and solving interface friction and wear debris production issues.

The friction and wear behavior of WC coating on medical grade titanium alloys

The clinical success of artificial joints has provided remarkable benefit to patients with joint disorders. However, the long-term success of total joint prostheses has been frustrated by an unacceptable rate of aseptic loosening, the osteolysis induced by joint wear, metal ion release, and high risk of toxicity. In this article, a hard and wear resistance WC coating was formed on the surface of medical grade titanium alloys, using a plasma spraying system in order to solve the above clinic problems. The WC phase and micro-hardness were characterized with X-ray diffraction and Vickers hardness tester to evaluate the plasma spraying process and the mechanical properties of the coatings. Then, the friction and wear tests of WC coatings were performed on M-2000 block-on-ring tribological testing machine. After that, the tribological behavior of the modified titanium alloys was investigated by means of scanning electron microscopy. It was observed that a graded structure was formed on the surface of titanium alloy and exhibited good bonding between the coating and substrate. In addition, it was noticed that WC phase could significantly harden the surface of titanium alloys and decreased the wear factor from 38.5 × 10−11 to 1.66 × 10−11 kg/Nm. Finally, it was proved that adhesion and abrasive wear dominated the damage of titanium alloy, while the wear of WC coating was controlled by adhesion wear. All of the results indicated WC coating on titanium alloys with good bonding strength after plasma spraying was a potential candidate for the application of artificial joints from the understanding of wear resistance. Further investigation regarding biocompatibility and artificial joint simulation need to be conducted.

Swing Friction Behavior of the Contact Interface Between CoCrMo and UHMWPE Under Dynamic Loading

CoCrMo alloy and UHMWPE have been widely used in knee joint prosthesis implantation materials. In this paper, swing friction behavior of the contact interface between CoCrMo alloy and UHMWPE is studied under dynamic loading. Swing friction characteristic and damage mechanism are discussed. The results show that swing friction coefficients increase with the rising of maximum normal load and swing angular amplitude. Unloading-standing could play alleviative roles in friction and wear to a large degree. As the cycle number gradually increases, the surface roughness of UHMWPE decreases, while the roughness of CoCrMo increases. During the swing friction, the main damage mechanism of CoCrMo is abrasive wear and the main damage mechanisms of UHMWPE are abrasive wear, fatigue wear and plastic deformation. Besides, it is easier to generate surface damages with small angle and heavy load.

Research on viscoelastic behavior and mechanism of hydrogel grafted with UHMWPE

ABSTRACT Hydrogel has been extensively studied for use as articular cartilage. The static and dynamic viscoelasticity behaviors of hydrogel grafted with ultra-high-molecular-weight polyethylene (UHMWPE) were studied by finite-element method (FEM) and dynamic mechanical analysis in this article. The results show that creep deformation presents an exponential function with the pore fluid velocity of hydrogel material. During the first period of stress relaxation, the internal fluid pore pressure of hydrogel material is less than partial pressure, which leads to the increasing fluid exudation, and the stress relaxation rate changes quickly. With the loss of fluid, the pore pressure and partial pressure achieve balance. Then, finally, stress relaxation reaches relative equilibrium. The storage modulus of hydrogel material increases with the increasing frequency, and there is a logarithmic regression between them. With the decrease in liquid–solid ratio, the storage modulus declines, while the loss modulus first increases and then decreases. When the strain increases, both storage modulus and loss modulus show an upward trend.