Jacek Senkara

Automatic investigation of surface phenomena in high temperature solid and liquid contacts

In the paper newly developed system for automatic measurements of surface properties is presented. The results obtained with the device described in this paper are far more accurate than those obtained by means of the currently applied non automatic methods based on the operators evaluation.

Computerized device with CCD camera for measurement of surface tension and wetting angle in solid-liquid systems

In this paper, a computerized device with the CCD camera for the automatic determination of important surface properties of liquid and solid in contact is described. This device is based on image processing algorithms. The system is capable of measuring the surface tension (surface energy) of liquid and the wettability of a solid surface in the wide range of temperatures, up to 1800/spl deg/C. The results obtained with this device are far more accurate than those obtained by means of the currently applied, extremely time consuming non-automatic methods and the operators subjective evaluation.

Suppressing cracking in resistance welding AA5754 by mechanical means

In this paper mechanical aspects of cracking during single- and multi-spot welding of AA5754 was investigated by both experimental and analytical approaches. The impact of mechanical loading on crack initiation and propagation was studied with the consideration of various process parameters including the loading imposed by electrodes, the formation of liquid nugget, and constraining factors during and after welding. Tensile properties of AA5754 and their dependence on the temperature were tested at room and up to solidus temperatures, in order to provide a reference of cracking stress. Thermalmechanical analysis was conducted based on the temperature field around the nugget and the state of stress encountered during welding. This analysis revealed that tensile stress might build up in the vicinity of the nugget during cooling, as explained in the experimental observation. General guidelines for suppressing cracking were proposed, i.e., to provide sufficient constraint around the weld spot during and after welding. @DOI: 10.1115/1.1418693#

Contemporary car body steels for automotive industry and technological guidelines of their pressure welding

The steels employed to-date by auto-makers for body-in-white manufacturing are discussed in the paper along with multi-structure materials of superb features (transformation-induced plasticity/twinning-induced plasticity effect steels). Technical suggestions are formulated for their welding by resistance spot method.

Computerized system for assessment of quality of solders

Computerized System for Assessment of Quality of Solders Dominik Sankowski, Jacek Senkara, Krzysztof Strzecha Absnacr Assumptions for building computerized system for assessment of quality of wlden are presented in this paper. This tester will allow to provide technologibl investigations within the framework of statandarired t n k for tho development of ne6 technologies and inspection of the implemented ones. parameters, and finally from the requirements to be met by a joint. . . II. PHYSICAL PRELIMINAR~ES

A review of Finite Element Analysis (FEA) of Resistance Spot Welding (RSW)

Modeling RSW was studied by many researchers with considering different electrical, thermal, and mechanical phenomena such as formation of temperature �耀eld and welding nugget growth. This paper is a review of the most important efforts in the �耀eld of FEA of RSW, by investigating present �耀nite element method (FEM) studies. After a brief introduction on FEA studies on RSW, such numerical solution methods as FEM and FDM (Finite Difference Method) are compared. Governing electrical, thermal, and mechanical equations are then discussed. A brief investigation about applicable algorithms is presented as a procedure for numerical solution. The importance of credible material properties is emphasized and predicted results in different studies are discussed. The �耀nal two parts are about recent issues in RSW FEA process and review of special cases such as multiple-sheet, single-sided welding, shunting effect, and covered models. Conclusions and suggestions about future studies are also provided.

Theoretical analysis of shunting effect in resistance spot welding (RSW) of AA2219

Abstract Shunting effect is the loss of electrical current via the secondary circuit provided due to existence of previous nugget in a series of welding spots. This phenomenon is important for products containing intermittent spots. In this study, a theoretical model is developed for shunting effect in resistance spot welding for aluminum alloy 2219. Welding distance together with welding current and time is included in the model to analyze the shunting effect on final nugget quality. Thermal and electrical interactions are considered in the model as well as geometrical aspects of the process. Temperature dependence of material properties, integration through the whole volume of the nugget and heat-affected zone, and assuming a simple cooling mechanism are the most important modifications designated in the proposed theoretical model. Predicted results of nugget diameter are compatible with experimental and finite element analysis results.

Comparative tests of plasma-surfaced nickel layers with chromium and titanium carbides

This article presents the results of structural tests of composite coatings on a NiSi2B alloy matrix containing carbides of Ti and Cr, which have been plasma surfaced from a powder mixture onto a low-alloyed steel substrate. The content and distribution of the strengthening phase in the matrix have been determined. It has been shown that the different nature of the interaction between Ti and Cr carbides and the liquid Ni alloy significantly affects the formation of composite surfacing layers as well as the distribution and content of strengthening phase particles in the matrix.