Key Engineering Materials Vol. 823

Abstract: It is well known that damage caused by wear and tear of the mechanical parts always seriously affect the accuracy of machinery. It is very important to improve the material properties of the mechanical elements. Anti-abrasion can improve the durability of machinery and equipment, thereby enhancing industrial competitiveness. Hence, it is important to establish the key technology of wear resistance for the related industries. Since the aluminum-silicon alloys are commonly used on the conditions of severe fretting wear, it is necessary to improve the fretting wear resistance before they are used. Therefore, effects of T6 heat treatment on fretting wear resistance of the aluminum-silicon alloys were investigated in this study. The experimental results of this paper will be very beneficial to the future of precision machinery and vehicle industry to develop more internationally competitive products.

Abstract: Amorphous carbonitride coatings (a-C:N and a-C:N:H) with dopant of niobium (Nb) were deposited on substrates of JIS SKH51 high speed steel (HSS) by a four-target close-field unbalance magnetron sputtering system. Subsequently, they were characterized by GDOS, XRD and XPS, and their corrosion resistance was comparatively evaluated. An electro-chemical tester was used to evaluate the corrosive behavior. An SEM was used to examine the test surface. The results revealed that the Nb dopant provided improvements in the corrosive performance to both the a-C:N and a-C:N:H coatings.

Abstract: CN-Nb, CN-Ti and CN-Zr that are respectively doped with Nb, Ti and Zr metal in a CN coating are deposited on SKH51 substrate using DC unbalanced magnetron sputtering (DC-UBM). The coatings’ chemical characterization, morphology, mechanical, tribological and corrosion properties are determined. The XRD analysis shows when a low content of metal is added, the coatings exhibit DLC structures. Result from the incorporation of metals, coatings performed denser texture. Simultaneously, the surface became smoother and denser while surface roughness varied from 0.036 to about 0.020 mm. Various properties are improved over CN coating, CN-Ti has a 64% greater hardness at 21.9 Gpa and adhesion 26% better, with a critical load of 87 N. The elastic recovery ranges from 68% (CN) to 100% (CN-Nb and CN-Zr), the wear rate varies from 0.51 10^-6mm³/Nm (CN) to 0.1 10^-6mm³/Nm (CN-Zr) and the wear depth is reduced by about 73%. An increase in the elastic recovery gives a decreased wear rate. In addition, the corrosion resistance is increased because there is a decrease in the corrosion current density and the CN-Zr coating performed about 35 times better than a CN coating.

Abstract: An elastic-plastic contact stress analysis is presented to study cyclic plastic deformation of surface hardened rolling elements under repeated contacts. The rolling contact is simulated by a Hertz contact loading moving across an elastic-plastic half-space. An exponential model with hardness varying with depth is employed for the surface hardened components, and the Chaboche nonlinear hardening rule is used to model cyclic plastic behavior of contact elements. Numerical results show that the hardened layer can effectively reduce the plastic deformation near contact surface. The contact elements with sufficient surface hardness may reach elastic shakedown state under repeatedly rolling contact. As the hardened layer reaches a certain depth, e.g. two times of half contact length, however, the effects of case depth on plastic strain and residual stress become negligible after hundred contact cycles.

Abstract: This research performs finite element simulations of cracked structures undergoing the vibrothermography process, which is an experimental technique gaining popularity for structural damage identification. In vibrothermography, a vibration shaker is used to excite the test structure. If the structure has cracks or defects, frictional heat will be generated at those cracks and thermal images can be recorded by an infrared camera. The vibrothermographical simulation includes modal analysis, transient vibration and transient thermal analysis. Two simulated examples are presented in this work: the first one is an aluminum-alloy plate with a hairline crack; the second example is a brake rotor with a hairline crack on one of the bolt-hole surfaces. Although higher modes are usually more difficult to excite, they may be used in vibrothermography to detect structural cracks more efficiently.

Abstract: It is popular to wear the contact lens nowadays. Also, the output value of the contact lens is estimated more than 4 billion NT dollar every year. Because the phenomena of the contact lenses are very complicated, the relevant mechanisms are not well understood. Thus, the security of contact lens needs to be further investigated. In the lubricated mechanism of the contact lens, there is a layer of tear between the contact lens and cornea. The contact lens’ behavior is akin to that of a slider bearing. The lens represents the slider, the eye plays the role of the stationary pad, and the tear film is the lubricant. Hence, hydrodynamics and contact mechanisms of a contact lens are quite a fascinating subject that is relevant to the science of tribology. In the paper, the lubrication mechanisms include the partial hydrodynamic lubrication (contact lens roughness), contact mechanics and Newtonian fluid mechanics have been established. The parameters of roughness, flow factor, tear film geometry, and hydrodynamic pressure distribution are discussed. The developed technology increases the safety of contact lens.

Abstract: Tinplate containers with high strength, good formability and corrosion resistance, has been widely used in food, beverages, grease, chemicals and other applications. In recent years, because of the significantly progress of tinplate container manufacturing technology, many tinplate cans have been opened in easy-open rings. However, a large number of food cans still use can openers as an important tool for opening cans. At present, in addition to the general traditional can opener is a single-edged knife in a lever manner, the other like roller, serrated or electric are driven by a gear wheel to rotate around the can to achieve the purpose of opening the can. Moreover, the wheel materials mainly are made from the stainless steels. To investigate wear characteristics on the can opener of the stainless steel of SUS 420J2, the experiments were conducted by the self-developed friction tester and its measure system in this study. According to the results, the effects of contact stress and sliding speeds on the wear of cutlery of the openers can be clarified.

Abstract: Electroless nickels have been used in practical applications as versatile materials for anti-wear. The wear resistance is well-improved as a composite coating by incorporating particles. Composite platting offers various mechanical and electoronic functions, depending on the combination of a material matrix and particles deposited. Among them Ni-P plating reinforced with SiC particles have been growing in importance owing to its high hardness and better anti-wear properties. In this study, a Ni-P-SiC/Ni-P-SiC system was evaluated using a ball-on-plate type reciprocating tester, and the results were compared with that of SiC/SiC system at room temperature. As the results, the Ni-P-SiC/Ni-P-SiC system with the surfaces where SiC particles were appeared in clumps had the low frictional coefficient around 0.1 even in water.

Abstract: This study describes the influence of flow properties of lithium soap greases on torque of small ball bearings. Three types of greases with different worked penetration were tested in this study. Their rheological properties are revealed by a cone plate type rheometer. Shear stresses under various shear rates are fitted with the Herschel-Bulkley equation. In addition, viscoelastic behaviors of the greases are measured by small amplitude oscillatory shear. The crossover stress that means the shear stress at G’=G” is obtained for the greases. Then, the bearing torque when three types of greases are used as a lubricant is measured. As the results, the grease with higher crossover stress shows the lower bearing torque regardless of that it has larger apparent viscosity. On the other hand, the grease with lower crossover stress shows the higher bearing torque regardless of that it has lower apparent viscosity. These results imply that the channeling state appears in the grease with higher crossover stress while the churning state appears in the grease with lower crossover stress.

Abstract: Accurate roundness or circularity measurement is essential to obtain correct functioning of assemblies, making roundness an important quality control parameter in manufacturing industry. Since circular motion while milling a circular work piece leads to quadrant glitches, a phenomenon familiar with existence of highly nonlinear friction behavior, roundness measurement was conducted to investigate this surface location error due to feed rate of the moving work table. This paper presents friction behavior on a milling process circular work piece in line resulted from identified surface error location (SLE).