Improving the Thermal Fatigue Strength of Hot-Working Tools by Laser Treatment

A method for increasing the thermal fatigue strength of a tool used in hot forming of bearing rings by applying circular laser tracks to the working surfaces is considered. Laser treatment is carried out with a power of 2.0...2.5 kW by applying on the end face working surface of the tool in the direction from the center to the periphery of the circular tracks with a common center coinciding with the center of the circumference of the end face; the tool is rotated at a constant angular rate, the spot diameter ds for each track is selected according to the dependence ds,i+1/ds,i = 0.85...0.90, and the laser radiation spots of adjacent tracks have a common point of contact. The results of pilot testing are presented, which confirmed the high technical and economic efficiency of the use of laser quenching for ejectors and punches. A tool made by machining, for example, an ejector of an AMP-70 automatic press, is subjected to volume quenching and tempering. The ejector material was steel 3Kh3M3F, quenching temperature in oil – 1030...1050 °С, tempering temperature – 580...610 °С. After volume quenching, additional machining is carried out, usually grinding, in order to remove the decarbonized layer of material formed during heat treatment and to give the working surface the required roughness class. The final stage in the tool manufacturing is the quenching of its working surface by laser treatment. Pilot testing showed that the use of laser treatment made it possible to increase the durability of ejectors of various types by 2 ... 3 times, of deforming punches – by 2.2 times.

GENERAL ANALYSIS OF STRESS AND DEFORMATION OF PARTS MOVING WITH HIGH VELOCITY IN A LIQUID OR GAS (REVIEW ARTICLE)

The article provides an analytical review and analysis of stresses and deformations of parts moving at high speeds in a liquid or gas. The working conditions of materials and parts of turbines (blades, rotor and casing) operating at high temperatures and loads are analyzed. The main ways of solving the problem of ensuring the strength of such parts are presented. The main ways to solve the problem of reliability of parts or the product as a whole are given: mathematical modeling (calculated determination of strength, durability and reliability); physical modeling (model testing); testing of full-scale products in reproducible real or operational conditions.It is impossible to speak about the strength of a part only from the calculation of deformations and stresses, even taking into account their change over time, so it is necessary to have strength criteria that establish the relationship between the strength parameters. It is emphasized that in the general case, the criterion of strength should answer the question: will the part collapse or not with the known laws of change in time of stresses, strains and temperatures It is shown that the considered standard characteristics of creep and long-term strength can be directly used in calculations only for those parts in which the uniaxial stress state at constant stresses and temperature is realized, when the working conditions of the material fully meet the test conditions of materials.An analytical view of deformation diagrams is considered as the main means of carrying out practical calculations of material strength. It is shown that in order to determine the stresses and strains in parts that move at high speeds in a liquid or gas, it is necessary to take into account the model of parts exploitation, the processes of creep and thermal fatigue of the material, and the unsteadiness of load processes. Keywords: stresses and deformations of turbine parts; deformation diagram; operating model of turbine parts; creep and thermal fatigue; nonstationarity of loading processes

Finite element analysis on the thermal fatigue life of full vs peripheral array packages

PurposeThis paper aims to examine the thermal cycling fatigue life performance of two-common solder array configurations, full and peripheral, using three-dimensional nonlinear finite element analysis.Design/methodology/approachThe finite element simulations were used to identify the location of the critical solder interconnect, and using Darveaux's model, solder thermal fatigue life was computed.FindingsThe results showed that the solder array type does not significantly influence thermal fatigue life of the interconnect. However, smaller size packages result in improved life by almost 45% compared to larger package designs. Additionally, this paper provided an engineered study on the effect of the number of rows available in a perimeter array component on solder thermal fatigue performance.Originality/valueGeneral design recommendations for reliable electronic assemblies under thermal cycling loaded were offered in this research.

Thermal Fatigue of Pwr Coolant System Loop Drain Lines Due to Outflow Activities

Thermal cycling induced fatigue is widely recognized as one of the major contributors to the damage of nuclear plant piping systems, especially at locations where turbulent mixing of flows with different temperature occurs. Thermal fatigue caused by swirl penetration interaction with normally stagnant water layers has been identified as a mechanism that can lead to cracking in dead-ended branch lines attached to pressurized water reactor (PWR) primary coolant system. EPRI has developed screening methods, derived from extensive testing and analysis, to determine which lines are potentially affected as well as evaluation methods to perform evaluations of this thermal fatigue mechanism for the U.S. PWR plants. However, recent industry operating experience (OE) indicate that the model used to predict thermal fatigue due to swirl penetration is not fully understood. In addition, cumulative effects from other thermal transients, such as outflow activities, may also contribute to the failure of the RCS branch lines. In this paper, we report direct OE from one of our PWR units where thermal fatigue cracking is observed at the RCS loop drain line close to the welded region of the elbow. A conservative analytical approach that takes into account the influence of thermal stratification, in accordance with ASME Class 1 piping stress method, is also proposed to evaluate the severity of fatigue damage to the RCS drain line, as a result of transients from outflow activities. Finally, recommendations are made for future operation and inspection based on results of the evaluation.

Simulation of mixing flows with different temperatures in a T-junction using OpenFOAM code

This paper aims to evaluate the frequency of velocity and temperature fluctuations in the mixing region using OpenFOAM code. Turbulent mixing of fluids at different temperatures can lead to temperature fluctuations at the pipe material. These fluctuations, or thermal striping, inducing cyclical thermal stresses and resulting thermal fatigue, may cause unexpected failure of pipe material. Therefore, an accurate characterization of temperature fluctuations is important in order to estimate the lifetime of pipe material. Thermal fatigue of the coolant circuits of nuclear power plants is one of the major issues in nuclear safety. To investigate thermal fatigue damage, the OECD/NEA-Vattenfall T-Junction Benchmark was initiated to test the ability of state-of-the-art Computational Fluid Dynamics (CFD) codes to predict the important parameters affecting high-cycle thermal fatigue in mixing tees. In this study, to simulate the standard problem described above, the OpenFOAM code is used, which is an open integrated platform for numerical simulation of problems in continuum mechanics. At the first with Salome-meca code, a computational grid was created, consisting of about 450,000 nodes, and k-eps model and RANS models were used to simulate turbulence. OpenFOAM code results were compared with the available experimental results. The results were found to be in well-agreement with the experimental results in terms of amplitude and frequency of temperature and velocity fluctuations.