An Experimental and Numerical Study of a CoNiCrAlY Coating Using Miniature Specimen Testing Techniques

Small punch tensile (SPT) tests have been carried out for a CoNiCrAlY coating at room temperature (RT), 500°C and700°C. Highly re-producible results have been obtained for SPT at 700°C while the formation of early cracking at lowertemperatures tends to compromise the repeatability of the tests. An alternative novel miniature specimen testingmethod has been developed and used for the miniature tensile tests of the CoNiCrAlY coating in the sametemperature range. Good agreements have been achieved between the SPT and miniature tensile testing resultsregarding the ductile to brittle transition temperature (DBTT). Excellent repeatability has been achieved over the fullrange of the temperature for the miniature tensile tests. An inverse approach has been developed and used to extractthe mechanical properties of the material from the miniature tensile tests, using a temperature-dependent Johnson-Cook model. Finite element (FE) modelling of the SPT tests, including damage evolution, has been carried out usingthe extracted material properties to give comparable predictions of the SPT testing results, such as the load displacementcurves and the approximate locations of the fracture failures

The mechanics of interface fracture in layered composite materials: (2) cohesive interfaces

The author’s mixed-mode partition theories [1-9] for rigid interfaces are extended to non-rigid cohesive interfaces for one dimensional (1D) interface fracture. In the absence of crack tip through thickness shear forces both classical and shear deformable partition theories have identical mode I and II energy release rate (ERR) partitions which are the same as those of shear deformable partitions for a mixed mode at rigid interfaces and independent of interface cohesive laws. Consequently, the mode mixity remains constant during fracture evolution. In the case of interface fracture in the layered isotropic materials, the pure modes in 2D elasticity partition theory only depend on the ratio between the penalty stiffness to the Young’s modulus of the materials and are independent of the shape of the cohesive laws. A mixed fracture mode can be readily partitioned by using the pure modes and a constant mode mixity is shown

Preliminary Investigation of Micro-V-Bending

Bending in sheet metal forming is defined as uniformly straining process around a linear axis. A V-bending process is normally used in sheet metal working due to the tool and process simplicity. The main problem in bending process is a springback occurrence which causes an error in part dimension. In a micro level, the springback angle is difficult to be assessed because of the influence of size effects in all aspects of the system. The springback behavior has been investigated in many previous kinds of research. However, the springback correction is still needed to be studied extensively so that it can be implemented reliably in micro-bending. The purpose of this research is to investigate the influence of punch velocity and holding time to the springback angle. The process is performed to the 0.1 mm thickness of copper foil. The punch velocities are 0.1 mm/s, 1 mm/s, and 10 mm/s. While the variation of holding time, which is set during the bottoming stage, are 7 s, 9 s, and 11 s. The result shows that the punch velocity clearly influences the springback angle. In addition, the holding time during the bottoming stage is a potential factor in springback angle correction

Failure Analysis of Cracking of Cast Aluminum Alloy Manhole Cover

In this paper, the abnormal fracture failure of a ZL104 aluminum alloy quick-opening manhole cover of a cement tank truck is systematically studied to discover the root cause of an accident. The unloading operation procedures of cement tank trucks, the effectiveness of safety valves, the chemical composition, mechanical properties and material quality of aluminum alloy manhole covers, and the macroscopic and microscopic morphology of fractures were comprehensively analyzed. The results show that although the Mg content in the chemical composition of an aluminum alloy manhole cover exceeds the standard, it is not the root cause of the accident. The root cause of the failure is that, during the unloading operation, the operator did not strictly follow the unloading procedures. One of the buckles was in the released state, which led to uplift cracking, resulting in the successive cracking and slipping of adjacent buckles, and the manhole cover finally cracked and flew out. Based on the failure causes, suggestions are put forward to prevent the manhole cover from failing during the unloading operation of cement tank trucks in the future

Study on Friction and Wear Properties of New Self-Lubricating Bearing Materials

In this paper, friction and wear tests were carried out: 45# steel (carbon steel) was rubbed with aluminum bronze, aluminum bronze-based inlaid solid self-lubricating bearing (ISSLB) material, tin bronze, and tin bronze-based ISSLB material under different loads. The friction and wear properties (friction coefficient, wear amount and friction temperature) of the above four materials were studied. The friction and wear properties of the new self-lubricating bearing material and the traditional copper alloy under the same load were compared. The friction mechanism of each material in the friction process was discussed. The effect and mechanism of C-MoS2 composite solid lubricant on friction and wear properties were analyzed. Under the experimental loads of 100 to 500 N, the average friction coefficients of aluminum bronze-based ISSLB material were maintained in the range of 0.18~0.14, while the average friction coefficients of tin bronze-based ISSLB material were maintained between 0.26~0.20, which is much lower than those of copper alloy. The wear amounts of tin bronze-based ISSLB material were always in the range of 14.7~34.4 mg, which were much less than those of aluminum bronze-based ISSLB materials and copper alloy. The results show that the copper-based ISSLB materials possess excellent wear resistance, and the friction and wear properties of tin bronze-based ISSLB material are better than that of aluminum bronze-based ISSLB material. Therefore, if the copper-based ISSLB materials are applied to self-lubricating bearings, the friction and wear resistance of bearings will be greatly improved and the service life of bearings prolonged

Study on Friction and Wear Properties of New Self-Lubricating Bearing Materials

In this paper, friction and wear tests were carried out: 45# steel (carbon steel) was rubbed with aluminum bronze, aluminum bronze-based inlaid solid self-lubricating bearing (ISSLB) material, tin bronze, and tin bronze-based ISSLB material under different loads. The friction and wear properties (friction coefficient, wear amount and friction temperature) of the above four materials were studied. The friction and wear properties of the new self-lubricating bearing material and the traditional copper alloy under the same load were compared. The friction mechanism of each material in the friction process was discussed. The effect and mechanism of C-MoS2 composite solid lubricant on friction and wear properties were analyzed. Under the experimental loads of 100 to 500 N, the average friction coefficients of aluminum bronze-based ISSLB material were maintained in the range of 0.18~0.14, while the average friction coefficients of tin bronze-based ISSLB material were maintained between 0.26~0.20, which is much lower than those of copper alloy. The wear amounts of tin bronze-based ISSLB material were always in the range of 14.7~34.4 mg, which were much less than those of aluminum bronze-based ISSLB materials and copper alloy. The results show that the copper-based ISSLB materials possess excellent wear resistance, and the friction and wear properties of tin bronze-based ISSLB material are better than that of aluminum bronze-based ISSLB material. Therefore, if the copper-based ISSLB materials are applied to self-lubricating bearings, the friction and wear resistance of bearings will be greatly improved and the service life of bearings prolonged

Nano blisters in multilayer Mo/Si coatings due to bombardment of hydrogen ions

Blistering is one of the major failures for multilayer coatings used in optical systems. By extending the blister mechanics theory of pockets of energy concentration, the nano blisters are studied on the surface of multilayer Mo/Si coatings subject to hydrogen ions bombardment. A mechanical model is developed to determine the mode I and II fracture toughness GIc and GIIc from experimental test data. By using the predicted values GIc and GIIc, the predicted trend lines between the blister radius and height agree very well with the test data.</p

Nano blisters in multilayer Mo/Si coatings due to bombardment of hydrogen ions

Conference slides presented at the 5th International Conference on Advanced Materials and Engineering Applications, Hebei University of Engineering, Handan China, 27-29 September, 2022.</p

Tribological properties of copper-embedded self-lubricating bearing materials

Purpose:  This study aims to investigate the effects of graphite-MoS2 composite solid lubricant on the tribological properties of copper-based bearing materials under dry conditions.  Design/methodology/approach:  The mixture of Graphite-MoS2 was inlaid in ZQSn6-6–3 tin bronze and ZQAl9-4 aluminum bronze matrix. These copper-embedded self-lubricating bearing materials were considered in friction pairs with 2Cr13 stainless steel, and their tribological properties were studied by using an MM200 wear test machine.  Findings:  The results show that the friction coefficients and wear rates of copper-embedded self-lubricating bearing materials are lower than those of the ordinary copper-based bearing materials. The wear performance of the tin bronze inlaid self-lubricating bearing material is better than that of the aluminum bronze inlaid self-lubricating bearing material. The wear mechanism of the tin bronze bearing material is mainly adhesive wear, and that of the aluminum bronze bearing material is mainly grinding wear, oxidation wear and adhesive wear. The copper-embedded self-lubricating bearing materials had no obvious abrasion, whereas the aluminum bronze inlaid self-lubricating bearing material exhibited deep furrows and obvious abrasion under high loads.  Originality/value:  These results are helpful for the application of copper-embedded self-lubricating bearing materials.</p