A new friction processing method for welding of dissimilar metals

Polyethylene FSSW/Adhesive hybrid single strap joints: Parametric optimization and FE simulation

: Focus: HOPE (FH) has developed the process parameters to successfully join AA6061 aluminum alloy and High Hardness Armor (HHA) steel using the friction stir process (FSP). Metallographic analysis conducted at the FH metallurgical laboratory, and later at the TARDEC metals lab, has confirmed that the dissimilar metals were metallurgically bonded at the joint surface with a thin (2-5 microns) Al-Fe intermetallic present. Mechanical load testing determined that the bimetallic FSP joint was stronger than similar AA6061-to-AA6061 fusion-welded and FSP joints. Initial process parameter trials were conducted to define the operating envelop for this FSP application. FH then evaluated the friction stir process parameters using an orthogonal array methodology. The parameters studied included tool rotation speed, tool traverse rate, tool tilt angle, plunge tool rotation speed, plunge rate, dwell, and joint offset. Other factors that were evaluated include tool design, fixture cooling, and auxiliary induction heating. In total 123 sets of process parameters were evaluated. Using the process parameter set which exhibited the greatest tensile strength FH produced a series of joint coupons which were then machined into test specimens for mechanical characterization. Metallographic samples were also prepared and analyzed using optical microscopy, scanning electron microscopy (SEM), electron back scatter diffraction (EBSD) and energy dispersive X-ray spectroscopy (EDS). This report also includes a description of the induction pre-heating system that was designed and demonstrated during this project for the potential use for FSP of high hardness metal alloys.

Understanding the key factors that contribute to transit travel times and travel-time variability is an essential part of transit planning and research. Delay that occurs when buses service bus stops, dwell time, is one of the main sources of travel-time variability and has therefore been the subject of ongoing research to identify and quantify its determinants. Previous research has focused on testing new variables using linear regressions that may be added to models to improve predictions. An important assumption of linear regression models used in past research efforts is homoscedasticity or the equal distribution of the residuals across all values of the predicted dwell times. The homoscedasticity assumption is usually violated in linear regression models of dwell time and this can lead to inconsistent and inefficient estimations of the independent variable coefficients. Log-linear models can sometimes correct for the lack of homoscedasticity, that is, for heteroscedasticity in the residual distribution. Quantile regressions, which predict the conditional quantiles, rather than the conditional mean, are non-parametric and therefore more robust estimators in the presence of heteroscedasticity. This research furthers the understanding of established dwell determinants using these novel approaches to estimate dwell and provides a relatively simple approach to improve existing models at bus stops with low average dwell times.

Evaluation of dissimilar metal joining of aluminum alloy to stainless steel using the filler metals with a high-entropy design

In the present paper, a tool with a flat pin was designed and utilized to friction stir spot weld acrylonitrile butadiene styrene sheets. Influences of welding parameters and pin geometries on joint morphology and mechanical performance were investigated. Results showed that rotational speed during plunging and stirring phase exerted a significant influence on the joint surface appearance and cross-sectional morphology while plunge rate and dwell time showed a slight effect. Secondary extrusion ring, rough weld surface, groove defects, and pores were observed under excessive stirring rotational speed. Spot weld diameter enlarged with the increase of the total tool rotation number in the plunging and stirring phase. Joint lap-shear tensile load varied significantly with the variation of the keyhole orientation. The comparison of the joints produced by different pin geometries showed that flat pin was optimal to fabricate joints with larger bonded region and lap-shear tensile load. With the increase of rotational speed or the decrease of plunge rate, joint shear strength reduced. The proper extension of dwell time under moderate rotational speed exerted a slight influence on the joint shear strength but showed a positive effect on the joint fracture load.

Friction assisted joining of aluminum and PVC sheets

The effect of cycling parameter variation (i.e. oxidation temperature, upper and lower dwell time, humidity in test gas) of the oxidation/spallation kinetics on four alloys was investigated within the framework of an EC funded research project (COTEST). For this purpose, specimens of AISI 441, Alloy 800H, CM 247 and P91 were subjected to thermocyclic testing in dry or humidified air. It was found that a minimum of 300 h accumulated hot dwell time is required for meaningful test results. Detailed characterisation of the corrosion products was performed using OM, SEM/EDX and XRD. The net weight change curves were evaluated with regards to the characteristic quantitative parameters describing oxide growth rate, time to onset of spallation/breakaway and weight of spalled oxide. Analysis of these values was made by the ANOVA method, which allows assessment of the significance of the roles of different test parameters and parameter variations on the oxidation/spallation kinetics from a limited number of experiments.

Bonding behavior during cold roll-cladding of tri-layered Al/brass/Al composite

Industrial requirements to establish metallic joints between dissimilar metals in the electric area. The ultrasonic welding process is an optimal process to joint thin sheets or foils. The goal of the research was to optimize the ultrasonic welding parameters to join thin nickel-coated copper sheets and aluminium sheets. It used a 0.5 mm thick high-purity copper (Cu-OF-R200) sheet coated with a 10 μm pure nickel layer and a 0.5 mm thick aluminium (1050A H24) sheet. The ultrasonic welding is made by a Branson Ultraweld L20 ultrasonic welder equipment. The mechanical properties and exacting geometrical tolerance of the joint were required. The welding parameter optimization is made empirically, with several welding tests. The optimal welding parameters were confirmed by non-destructive and destructive tests of the joints. The non-destructive tests were the visual inspection and geometrical measurements of the joint sizes. The destructive tests were tensile tests and macroscopic and microscopic tests. The completed test results confirmed the process applicability and the quality of the joint.

Thermal cycling (TC) is an important method to evaluate the reliability of electronic products. During the TC process, the solder joints have the risk of cracking due to fatigue stress, but the internal interfaces in the package will also be affected by the fatigue loads, presenting delamination at several interface areas. Due to the difficulty in experimental monitoring of delamination and the lack of effective simulation methods, the research on evaluating the risks of interface delamination has outstanding deficiencies during the TC process. This paper uses finite element analysis (FEA) to evaluate the risk of interface delamination of the underfill (UF) during TC. The viscoelastic property of UF is introduced in FEA. The stress and strain at the interface are carefully analyzed during TC, and the accumulated strain energy (ASE) at the risk position of the interface is calculated as the characteristics reflecting the damage of UF at the interface during TC. In addition, the influence of the coefficient of thermal expansion (CTE) of UF, the dwell time, and the stress-free temperature on ASE are systematically analyzed. This study provides a method for the qualitative and quantitative assessment of the risk of delamination for UF during TC.

Purpose: High Dose Rate (HDR) brachytherapy poses a special challenge to radiation safety and quality assurance (QA) due to its high radioactivity, and it is thus critical to verify the HDR source location and its radioactive strength. This study demonstrates a new method for measuring HDR source location and radioactivity utilizing thermal imaging. A potential application would relate to HDR QA and safety improvement. Methods: Heating effects by an HDR source were studied using Finite Element Analysis (FEA). Thermal cameras were used to visualize an HDR source inside a plastic applicator made of polyvinylidene difluoride (PVDF). Using different source dwell times, correlations between the HDR source strength and heating effects were studied, thus establishing potential daily QA criteria using thermal imaging Results: For an Ir1?2 source with a radioactivity of 10 Ci, the decay-induced heating power inside the source is ∼13.3 mW. After the HDR source was extended into the PVDF applicator and reached thermal equilibrium, thermal imaging visualized the temperature gradient of 10 K/cm along the PVDF applicator surface, which agreed with FEA modeling. For Ir192 source activities ranging from 4.20–10.20 Ci, thermal imaging could verify source activity with an accuracy of 6.3% with a dwell time of 10 sec, and an accuracy of 2.5 % with 100 sec. Conclusion: Thermal imaging is a feasible tool to visualize HDR source dwell positions and verify source integrity. Patient safety and treatment quality will be improved by integrating thermal measurements into HDR QA procedures.

The evolution of global and local stress/strain conditions in test fasteners under test conditions is investigated using elastic-plastic, time-dependent finite element analyses (FEA). For elastic-plastic response, tensile data from multiple specimens, material heats and test temperatures are integrated into a single, normalized flow curve from which temperature dependency is extracted. A primary creep model is calibrated with specimen- and fastener-based thermal relaxation data generated under a range of times, temperatures, stress levels and environments. These material inputs are used in analytical simulations of experimental test conditions for several types of fasteners. These fastener models are constructed with automated routines and contact conditions prescribed at all potentially mating surfaces. Thermal or mechanical room temperature pre-loading, as appropriate for a given fastener, is followed by a temperature ramp and a dwell time at constant temperature. While the amount of thermal stress relaxation is limited for the conditions modeled, local stress states are highly dependent upon geometry (thread root radius, for example), pre-loading history and thermal expansion differences between the test fastener and test fixture. Benefits of this FE approach over an elastic methodology for stress calculation will be illustrated with correlations of Stress Corrosion Cracking (SCC) initiation time and crack orientations in stress concentrations.

Characterising Residual Stresses in a Dissimilar Metal Electron Beam Welded Plate

The formation mechanism of nanocrystalline TiC from KCl–LiCl molten salt medium

Objective. The purpose of this study was to characterize and to evaluate the effect of thermal treatment on properties and bioactivity of experimental dental cement. Methods. Specimens of the dental cement (pellets 13 mm in diameter × 3 mm thick) were prepared by cold pressing of micronized powder of set Alborg White Portland cement. The thermo-gravimetric analysis and differential scanning calorimetry (TGA/DSC) were used to analyze the phase composition and determine the transition temperatures for sintering process. The effect of heat rate and dwell time on density, crystal morphologies, crystalline phases and elemental composition of cement was evaluated by scanning electron microscope (SEM), X-ray diffraction (XRD), X-ray fluorescence (XRF) and micro-Raman spectroscopy. The bioactivity of set and heat-treated cements was evaluated by ability produce the hydroxyapatite (HA) layer on a surface of specimen immersed in a simulated body fluid (Dulbecco’s Phosphate-Buffered Saline (DPBS). The formation of hydroxyapatite was confirmed by SEM, X-ray energy dispersive spectroscopy (EDS), XRD and and micro-Raman spectroscopy. The amount of produced HA was measured by weight method after 1, 3, 7, and 14 days of immersion. Results. The set of samples were sintered from experimental dental cement at various heating rate and dwell time. The highest density was obtained at slower heating rate and longer dwell time. The heat treatment changes the hydration phases without changing elemental composition. The heat treatment significantly improves biological performance of dental cement. The heat-treated cement produces 10 times more HA with immersion into simulated body fluid.