Jacek Senkara

Bio: Jacek Senkara is an academic researcher from Warsaw University of Technology. The author has contributed to research in topics: Welding & Spot welding. The author has an hindex of 10, co-authored 48 publications receiving 718 citations. Previous affiliations of Jacek Senkara include University of Toledo & University of Michigan.

Resistance welding : fundamentals and applications

Abstract: WELDING METALLURGY Solidification in Resistance Spot Welding Phase Transformations in RSW Cracking References ELECTROTHERMAL PROCESSES OF WELDING Introduction Electrical Characteristics of Resistance Welding Thermal Characteristics of Resistance Welding Heat Balance Electrode Life Lobe Diagrams References WELD DISCONTINUITIES Classification of Discontinuities Void Formation in Weld Nuggets Cracking in Welding AA6111 Alloys Cracking in Welding AA5754 Alloys References MECHANICAL TESTING Introduction Shop Floor Practices Instrumented Tests References RESISTANCE WELDING PROCESS MONITORING AND CONTROL Introduction Data Acquisition Process Monitoring References WELD QUALITY AND INSPECTION Weld Quality Attributes Destructive Evaluation Nondestructive Evaluation References EXPULSION IN RESISTANCE SPOT WELDING Influence of Expulsion on Spot Weld Quality Expulsion Process and Detection Expulsion Prediction and Prevention Examples References INFLUENCE OF MECHANICAL CHARACTERISTICS OF WELDING MACHINES Introduction Mechanical Characteristics of Typical Spot Welders Influence of Machine Stiffness Influence of Friction Influence of Moving Mass Follow-Up in a Welding Cycle Squeeze Time and Hold Time Measurement Other Factors References NUMERICAL SIMULATION IN RESISTANCE SPOT WELDING Introduction Coupled Electrical-Thermal-Mechanical Analysis Simulation of Contact Properties and Contact Area Simulation of Other Factors Modeling of Microstructure Evolution Examples of Numerical Simulation of RSW Processes References STATISTICAL DESIGN, ANALYSIS, AND INFERENCE IN RESISTANCE WELDING RESEARCH Introduction Basic Concepts and Procedures Experiments with Continuous Response Experiments with Categorical Responses Computer Simulation Experiments Summary References INDEX

Expulsion prediction in resistance spot welding

Abstract: An expulsion model has been developed for resistance spot welding, based on consideration of the interaction between mechanical and metallurgical processes during welding. An expulsion criterion is proposed by comparing the electrode force with that from the liquid nugget: expulsion occurs when the latter exceeds the former. An effective electrode force, instead of an applied/ nominal electrode force, is used in the criterion. This force can be calculated based on the applied electrode force and its offset from the liquid nugget force, which can be obtained through knowledge of the internal pressure and the dimensions of a nugget. Pressure components in a molten metal include those due to melting, liquid expansion, vapor pressure, and decomposition of surface agents, and are formulated by thermodynamic considerations. Experiments have been conducted to verify the model on an aluminum alloy (AA5754), and good agreement was achieved. The model can also be used to develop guidelines for electrode force selection.

Cracking in spot welding aluminum alloy AA5754

Abstract: The phenomenon of cracking was observed during resistance spot welding a commercial aluminum alloy AA5754, and mechanisms of cracking and healing are discussed in this paper Metallographic study of welded coupons revealed cracks located on only one side of a weldment in the heat-affected zone (HAZ), with respect to the welding sequence. Cracks are visible from longitudinal cross sections only. Some of them are partially or fully filled. Crack appearance and orientation are fairly repeatable and their intergranular characteristics and dendritic fracture surface morphology prove they were formed at elevated temperatures in the presence of liquid metal. The discussion of metallurgical factors considering the Al-Mg equilibrium phase diagram and the possible temperature histories of various zones in a weldment during spot welding elucidated the approximate conditions for cracking during spot welding and for mending the structure. A thermomechanical analysis revealed a high possibility for tensile stress huildup on the cracked side of the weldments as a result of material flow, thermal stress development and localized straining.

A statistical analysis of expulsion limits in resistance spot welding

Abstract: Expulsion is an important phenomenon in resistance spot welding. It involves loss of metal from the liquid nugget, which often results in the reduction of weld strength. Various models have been proposed to understand expulsion mechanisms. In these models the occurrence of expulsion is often treated as a deterministic event, and depicted by a line (boundary) in conventional lobe diagrams. In this study, statistical analysis is employed to explore expulsion with consideration of the influence of random factors. Models are built based on experimental data, and one steel and two aluminum alloys are used as examples. Expulsion probabilities are presented as a function of electrode force, welding current, and time. Analytical models and their graphical form of expression (contours and surfaces) are created to present expulsion limits under various combinations of welding parameters. This study provides not only quantitative model predictions on expulsion limits for the materials studied, but also a generic statistical methodology that can be used for analyzing expulsion in various material systems.

Resistance Welding: Fundamentals and Applications, Second Edition

Abstract: Drawing on state-of-the-art research results, Resistance Welding: Fundamentals and Applications, Second Edition systematically presents fundamental aspects of important processes in resistance welding and discusses their implications on real-world welding applications. This updated edition describes progress made in resistance welding research and

One-Dimensional Metal-Oxide Nanostructures: Recent Developments in Synthesis, Characterization, and Applications

Abstract: 1D metal-oxide nanostructures have attracted much attention because metal oxides are the most fascinating functional materials. The 1D morphologies can easily enhance the unique properties of the metal-oxide nanostructures, which make them suitable for a wide variety of applications, including gas sensors, electrochromic devices, light-emitting diodes, field emitters, supercapacitors, nanoelectronics, and nanogenerators. Therefore, much effort has been made to synthesize and characterize 1D metal-oxide nanostructures in the forms of nanorods, nanowires, nanotubes, nanobelts, etc. Various physical and chemical deposition techniques and growth mechanisms are exploited and developed to control the morphology, identical shape, uniform size, perfect crystalline structure, defects, and homogenous stoichiometry of the 1D metal-oxide nanostructures. Here a comprehensive review of recent developments in novel synthesis, exceptional characteristics, and prominent applications of one-dimensional nanostructures of tungsten oxides, molybdenum oxides, tantalum oxides, vanadium oxides, niobium oxides, titanium oxides, nickel oxides, zinc oxides, bismuth oxides, and tin oxides is provided.

Critical review of automotive steels spot welding: process, structure and properties

Abstract: Spot welding, particularly resistance spot welding (RSW), is a critical joining process in automotive industry. The development of advanced high strength steels for applications in automotive industry is accompanied with a challenge to better understand the physical and mechanical metallurgy of these materials during RSW. The present paper critically reviews the fundamental understanding of structure–properties relationship in automotive steels resistance spot welds. The focus is on the metallurgical characteristics, hardness–microstructure correlation, interfacial to pullout failure mode transition and mechanical performance of steel resistance spot welds under quasi-static, fatigue and impact loading conditions. A brief review of friction stir spot welding, as an alternative to RSW, is also included.

Joining of engineering ceramics

Abstract: Engineering ceramics such as alumina, zirconia, silicon nitride and silicon carbide can now be manufactured reliably with reproducible properties As such, they are of increasing interest to industry, particularly for use in demanding environments, where their thermomechanical performance is of critical importance, with applications ranging from fuel cells to cutting tools One aspect common to virtually all applications of engineering ceramics is that eventually they must be joined with another material, most usually a metal The joining of engineering ceramics to metals is not always easy There are two main considerations The first consideration is the basic difference in atomic bonding: the ionic or covalent bonding of the ceramic, compared to the metallic bond The second consideration is the mismatch in the coefficient of thermal expansion In general, ceramics have a lower coefficient of thermal expansion than metals and, if high tensile forces are produced in the ceramic, either a

Failure mode transition in AHSS resistance spot welds. Part I. Controlling factors

Abstract: Failure mode of resistance spot welds is a qualitative indicator of weld performance. Two major types of spot weld failure are pull-out and interfacial fracture. Interfacial failure, which typically results in reduced energy absorption capability, is considered unsatisfactory and industry standards are often designed to avoid this occurrence. Advanced High Strength Steel (AHSS) spot welds exhibit high tendency to fail in interfacial failure mode. Sizing of spot welds based on the conventional recommendation of 4t0.5 (t is sheet thickness) does not guarantee the pullout failure mode in many cases of AHSS spot welds. Therefore, a new weld quality criterion should be found for AHSS resistance spot welds to guarantee pull-out failure. The aim of this paper is to investigate and analyze the transition between interfacial and pull-out failure modes in AHSS resistance spot welds during the tensile–shear test by the use of analytical approach. In this work, in the light of failure mechanism, a simple analytical model is presented for estimating the critical fusion zone size to prevent interfacial fracture. According to this model, the hardness ratio of fusion zone to pull-out failure location and the volume fraction of voids in fusion zone are the key metallurgical factors governing type of failure mode of AHSS spot welds during the tensile–shear test. Low hardness ratio and high susceptibility to form shrinkage voids in the case of AHSS spot welds appear to be the two primary causes for their high tendency to fail in interfacial mode.

Effects of weld microstructure on static and impact performance of resistance spot welded joints in advanced high strength steels

Abstract: Evaluating the impact performance of resistance spot welded joints in advanced high strength steels (AHSS) is critical for their continued integration into the automotive architecture. The effect of strain rate on the joint strength and failure mode is an important consideration in the design of welded structures. Recent results suggest that the failure mode is dependent upon the strength, chemistry, and processing of AHSS. Current literature, however, does not explain the effects of weld microstructure and a comprehensive comparison has yet to be conducted. The present study details the fracture paths within the joint microstructure of spot welded AHSS, including dual phase (DP), transformation induced plasticity (TRIP) and ferritic–bainitic (FB), in comparison to new high strength low alloy steels. Quasi-static and impact tests were conducted using a universal tensile tester and an instrumented drop tower respectively. Results for elongation, failure load and energy absorption for each material ...