Robert Ulewicz

Fatigue Strength of Ductile Iron in Ultra-High Cycle Regime

Machine and equipment safety is the most essential factor that determines the choice of a particular material used in the construction phase. Failure analyses in engineering praxis demonstrate that nearly 90 % of all cases of failures are caused by fatigue. For popular technical applications such as cars and trains, the durability expected for some components ranges from 108 to 1010 loading cycles. However, only few studies have been carried out for more than 107 cycles. The SN curve in the ultra-wide life region must be determined in order to ensure actual fatigue strength and safety of these components. This paper presents the results obtained from fatigue tests carried out by means of a high-frequency fatigue testing machine for the three grades of ductile iron: with ferritic-pearlitic matrix (GGG50), with pearlitic-ferritic matrix (GGG60) and ADI cast iron in the range from 106 up to 1010 cycles.

Identification of problems of implementation of Lean concept in the SME sector

Abstract The article presents identification of problems during the implementation of Lean concept in small and medium-sized enterprises in Poland. Although the Lean methodology is recognized all over the world as one of the best and most effective ways to improve the functioning of enterprises, in Polish conditions exist serious problems with its implementation. Development of small and medium-sized enterprises is regarded as one of the measures of economic growth and a sign of healthy competition. The needs of the economy and the limited resources characterizing this enterprise sector imply the need to adjust its capacities to the requirements of the turbulent environment. In the analysis of problems there were used the results of questionnaire surveys conducted among representatives of the companies participating in the largest Lean conference in Central Europe.

Quality Management in the Process of Selection of Material for Dump Truck Elements

Abstract The article presents the problem of quality management in the process of material selection for structural elements of a car dump truck. The study took into account the classical management pyramid and there was used the optimization method (generalized objective function). The center that manages the process of production / assembly of the dump truck should be the level of organization that has the highest degree of processing of required information and making strategic decisions in this respect. The design process of structural elements is carried out primarily in terms of the ability to provide adequate physical and mechanical properties in the process. There is a very strong tendency to reduce the own weight of the semi-trailers by increasing the weight of the load. This is an important criterion from the point of view of the economics of operation of technical facilities of this type. The article presents the results of the application of a generalized objective function in the field of material selection for construction elements of a dump truck. The analysis includes structural elements made of S355 steel and Hardox 400 and 450 fine-grain steel.

The Empirical Assessment of the Convergence Rate for the Bootstrap Estimation in Design of Experiment Approach

Design of experiment (DoE) is a set of practical recipes and theoretical assumptions leading to the optimization of the technological process and/or the stabilization of its output quality. Practically, all the DoE approaches assume the normality of a random noise and the quasi-linearity of models taken from the general linear model (GLM) class. It allows to use traditional least-square methodology to identification of a model parameters and their confidence intervals. It gives usually sufficient results but completely fails if the model is not from GLM class or a random noise has not a normal distribution. The solution for such problems is the bootstrap approach, a resampling method based on Monte Carlo strategies. This paper tries to answer a question how many repetitions should be made to estimate parameters of the prediction model with sufficient accuracy.

Influence of Electrodeposited Coatings on Ultra-High-Cycle Fatigue Life of S235 Structural Steel

The article deals with experimental results of fatigue life of plain carbon steel electrodeposited with nickel, chromium and iron-zinc coatings in the ultra-high-cycle region of loading (N = 6×106 ÷ 1010 cycles) obtained at high-frequency fatigue testing (f ≈ 20 kHz, T = 20 ± 5 °C, R = -1). The results confirm continuous decrease of S-N curves after N = 107 cycles. Electrodeposited coatings caused decrease of the fatigue life in the low and high-cycle fatigue region. In the ultra-high cycle region the influence of electrodeposited coatings on fatigue properties is negligible. There was observed no significant influence of thickness of electrodeposited coatings on fatigue lifetime decrease.

Analysis of Structure of Elements for Automotive Industry

The paper presents the results of the structure and chemical composition of materials used to manufacture of gear wheel for the automotive industry. Analyzed gear wheel that is a part of one of the mechanical systems of an automotive vehicle was made of sinter Sint-D 32 in the technology of powder metallurgy and alloy structural steel for quenching and tempering 42CrMo4. The cause of the analysis was to research for an alternative material for sinter Sint-D 32 after identified low static strength according to the requirements applicable in the automotive industry. For the analysis were used standard test methods applicable in materials science. Based on microstructure and mechanical properties analysis performed according to requirements applicable in the automotive industry, the research found that steel 42CrMo4 is relevant material to be used in serial production for this particular gear wheel.

Optimization of the Selection Process of Galvanic Coatings

Processes of electrolytic application of metals are used in order to obtain pure coatings, single - or multilayer. Appropriate selection and proper execution contribute to the improvement of product quality, which affects its proper and long functioning. Production costs are not necessarily high. They depend mainly on the proper selection of the coating. The article presents the results of the use of generalized objective function for selection of galvanic coating on metal parts. There were used following criteria in order to characterize the quality (usability): corrosion resistance, mechanical properties, physical properties, gloss, roughness, and economical criteria. Presented method of determining the objective function can be used to choose the optimal coatings for specific service conditions or customer requirements. Presented method of determining the objective function in the design process of the surface layer makes it possible to assess the impact of various factors on the quality of the product and thus gives a chance to make the right choice.

Performance Evaluation of the Production Control Systems of Push and Pull Type

In the article there was undertaken an attempt to assess the functioning of the production control systems based on the analysis of selected companies of widely understood metal industry. Based on the literature as well as own research there was carried out comparative analysis of selected pull and push systems. There were described conditions, which must be met by production system, that a given method bring expected results and guarantee the achievement of measurable benefits resulting from improving the organization of the flow of materials and information. Carried out analysis indicates differences in key areas and draws attention to the conditions, which should be met by production environment that a given system can function properly.