Main Failure Form Research Articles

Research on the Fracture and Breakage of Heavy-Duty Turning Tool for Rough Machining Hydrogenated Cylindrical Shell

Analyzing and researching the main failure forms of the hard alloy turning tool in rough machining process of the hydrogenated cylindrical shell’s blank. Then the cutting experiments were done at the site, and the results showed that the main failure forms of the hard alloy turning tool in rough machining process of the blank were tools’ fracture. However the main reason leading into this phenomenon was the mechanical impact of variable frequency and variable load which was caused by the dynamic change of cutting dosage. Integrating the experiment results, and combining the principles of elasticity and the principles of fracture toughness of hard alloy, the measures of protecting the tools from being fractured prematurely in heavy cutting process were worked out, then the research result would provide reference database for practical production.

Experimental Study on Bit Tooth Made of Nano-Cemented Carbide Composites in Air Hammer Drilling

It is fracture, wear and abscission of bit tooth that make up of the main failure forms for the air hammer bit, which have badly restricted the further popularization and application of the air hammer drilling. The main reason is that the ordinary cemented carbide tooth is difficult to meet the complex conditions of the air the hammer drilling. Therefore, this research puts forward a new thought that we strengthen the carbide tooth by adding the nano-Al2O3into the substrate materials of WC-Co. According to the study of several formulas of nano-composites, the test of sample performance, experimental study of impact abrasive wear and microstructure, we draw some conclusions that adding amount of nano-Al2O3can refine grain, make microstructure more uniform and improve the wear resistance of composites, but also can enhance the strength of boundaries of WC-Co and transform the fracture form from the intergranular fracture to the transgranular fracture. Meanwhile, it can also improve nano-composites comprehensive performance by adding rare earth. The result for site test of bit shows that comparing with the bit equipped the original carbide teeth, the efficiency of rock breaking of the bit equipped nano-composites teeth increase by 20% and the service life increase by 80%.

Fatigue Propagation Lifetime Prediction of Rotary Kiln Weld Shell

Rotary kin shell is welded by cylindrical steel plates. Crack propagation of weld toes near supporting rollers until final fracture is the main failure form. Based on fracture mechanics, an overall intensity factor with regard to circumferential stress, concentrated stress, residual stress, and temperature stress is used to asses the crack growth. Under complex overloading conditions, the major factor, namely, circumferential stress across shell, is calculated by using finite element (FE) code ANSYS. Concentrated stress, residual stress, and temperature stress play a major role in the fatigue growth behavior, thus their effects are considered in a theoretical analysis to be included in the overall intensity factor. A certain extent good lifetime results are obtained compared with practical observation. This paper presents a reasonable procedure to evaluate propagation lifetime of weld shell, and the results are quit significant for equipment daily maintenance of rotary kiln.

Design and Simulation of the Hydraulic System for the Rock Hob Test-Bed

Rock tunnel boring machine is one of the main machineries and equipments for underground engineering ,and the failure of tool systems is the main failure form of this machinery. Rock hob test-bed is the only testing equipment for tool failure and wear. In this paper, the hydraulic-driven system of the rock hob test bench is designed and simulated, and the effect of load and flow rate of hydraulic oil in this hydraulic system on characteristics of this test-bad is analyzed. The results show that the horizontal movement speed of test bench is directly proportional to the flow rate, but the effect of the load on this speed can be ignored; the delay of the movement of the test bench are proportional to the load. These results are very helpful to the structure optimization of tool system and the improvement of working efficiency.

The Wear Resistance of Pack-Boronizing of the Oilstone Forming Die

The main failure forms of oilstone forming die is serious wear on the work face, so the key point to extend the use life of die is how to control the wear. In order to improve the hardness and resistance to wear and prolong the use life of the oilstone forming die, the boronizing technology was used on the work face of the oilstone forming die. There are some of elements such as B、C、Al、Cr、Si and Fe etc in boronizing layer, all of them change their contents during boronizing. Maximum value of microhardness of boronizing layer appears in subsurface, not in surface, and lows along depth of boronizing layer. The abrasion resistance of boronizing layer comes out maximum after quenching and tempering. After quenching and tempering, the lifetime of the oilstone forming die with boronizing is greatly improved.

Effects of Nano-Al<sub>2</sub>O<sub>3</sub>p on Thermal Shock Behaviors of NiCoCrAlY Coatings by Laser Cladding

NiCoCrAlY coatings strengthened by different content of nano-Al2O3p, using crosscurrent CO2 laser, were prepared on Ni-based superalloy substrates, and thermal shock behaviors of these coatings were investigated by cycling between 1050°C and room temperature (forced water quenching).The results show that the thermal shock resistances of nano-Al2O3p-added coatings are definitely better than that without adding nano-Al2O3p. Among the nano-Al2O3p-added coatings, the coating added with 0.5wt% nano-Al2O3p performs best. After 10 thermal shock cycles, the spalled and spalling area in the oxide scale of the no-nano-Al2O3p coating reaches up to 27.7%, and the main failure form of the oxide scale is an expanding unit-spalling type in thermal shock cycles. While the area in the oxide scale of nano-Al2O3p-added coatings is only 10%~60% to the no-nano-Al2O3p one, and the failure of these oxide scales is mainly in the form of unit-spalling type. After 100 thermal shock cycles, many cracks turn up in the cross-section of the no-nano-Al2O3p coating, including propagating crack and internal crack. While no internal crack appeared in nano-Al2O3p-added coatings, and the propagating cracks are smaller than no-nano-Al2O3p one.

Reliability Design Method for Interference Joint in Mechanical Engineering

The plastic deformation as a main form of failure of Interference Joints may happen in engineering works if it is designed unreasonably. In this paper, the contact stress and the strength of Interference Joint parts were analyzed deeply. Based on the theory of the reliability design, the general formulas and the method of the reliability design and computation for Interference Joint were established in consideration of joint structure, machining precision, interference value, mechanical properties of the joint parts and their randomicity. The practical design method, which would promote the reliability of Interference Joint effectively, was proposed for larger size and some other important Interference Joints. Compared to the conventional design method, the working reliability of Interference Joints can be improved obviously by means of the reliability design method.

Analysis of the structural characteristics of an intermediate rail vehicle and their effect on vehicle crash performance

In the current paper, the authors present an analysis of the structural characteristics of an intermediate rail vehicle and their effects on crash performance of the vehicle. Theirs is a simulation based analysis involving four stages. First, the crashworthiness of the vehicle is assessed by simulating an impact of the vehicle with a rigid wall. Second, the structural characteristics of the vehicle are analysed based on the structural behaviour during this impact and then the structure is modified. Third, the modified vehicle is tested again in the same impact scenario with a rigid wall. Finally, the modified vehicle is subjected to a modelled head-on impact which mirrors the real-life impact interface between two intermediate vehicles in a train impact. The emphasis of the current study is on the structural characteristics of the intermediate vehicle and the differences compared to an impact of a leading vehicle. The study shows that, similar to a leading vehicle, bending, or jackknifing is a main form of failure in this conventionally designed intermediate vehicle. It has also been found that the location of the door openings creates a major difference in the behaviour of an intermediate vehicle. It causes instability of the vehicle in the door area and leads to high stresses at the joint of the end beam with the solebar and shear stresses at the joint of the inner pillar with the cantrail. Apart from this, the shapes of the vehicle ends and impact interfaces are also different and have an effect on the crash performance of the vehicles. The simulation results allow the identification of the structural characteristics and show the effectiveness of relevant modifications. The conclusions have general relevance for the crashworthiness of rail vehicle design.

A Reliability Analysis Based on Fatigue Strength of Open-Mill Rollers

The two-roller mill is a basic processing machine in polymer industry, and the rollers are one of its important working parts. In the present paper, the working process of the mill roller used in plasticization of polymers and its failure mode is analyzed. The bending stress, shear stress, and resultant stress at the critical section of the mill roller are calculated to obtain its fatigue strength, and the corresponding diagram of fatigue limit graph is drawn. Based on the conclusion that fatigue failure is the main form of failure of the mill roller, a reliability analysis is applied to the fatigue strength of the mill roller and the reliability parameter is worked out. From example, it shows that the reliability of the mill roller is very high. Therefore, the working load may be increased appropriately.

Numerical and experimental distribution of temperature and stress fields in API round threaded connection

Thread galling is one of the main failure forms for oil tubing and casing connections, and it leads to deterioration of seal performance and connection strength of oil tubing and casing directly. A series of full-scale tests were performed on samples of API J55 steel grade non-upset tubing threaded connections. The temperature and stress field distributions of the tubing threaded connection were measured dynamically under the action of different make-up and break-out torque and velocity. Major factors, which affect the distributions of temperature and stress fields of tubing connections, were studied and their effects on thread galling failure were summarized with friction-wear theory. The FEA models of tubing threaded connections are validated by comparing the numerical results with the full-scale tests. The validated models are afterwards used to perform parametric studies on the connection behaviour.

Study of wear behavior of MoSi 2 under water lubrication

Molybdenum disilicide (MoSi 2) has been synthesized by mechanical alloying, and then shaped by HP. The phase and microstructure of the product have been analyzed by X-ray and SEM. The tribological properties of MoSi 2 against steel under water lubrication were investigated. Under this condition, the friction coefficient was much lower and the wear rate of MoSi 2 was higher than that of under dry sliding condition. The wear behaviour of the surface of MoSi 2 under water lubrication was observed by SEM, and it indicated that fatigue wear was the main failure form of this material, although part adhere phenomenon was also found at high load.

Phenomenology of surface failure of poly(methylmethacrylate) resulting from rolling contact fatigue

AbstractResults of phenomenological study into the forms of surface failure of poly(methylmethacrylate) (PMMA) are presented. Surface failure of the polymer resulted from rolling contact fatigue produced in a model configuration consisting of a PMMA disc with nominally flat surface loaded against three steel balls able to roll free over the surface of the disc. It was found that the performance of the polymer under the test conditions used is influenced by lubricating medium and the main form of failure is of surface fatigue type. © 1995 John Wiley & Sons, Inc.