Design and Commissioning of a Friction Welding Machine

An experimental lightweight linear friction welding machine was designed and commissioned. The machine was designed to explore higher frequencies of oscillation (up to 1 kHz) than those commercially available, for a number of different amplitudes of oscillation. During the commissioning stage problems related to rig stiffening were recognized and the operating envelope of the machine was identified. Important friction welding process parameters like stress and temperature are monitored to evaluate process development and weld integrity.     

On the Strain Rate Sensitivity of Abs and Abs Plus Fused Deposition Modeling Parts

In this work the effect of strain rate on the tensile strength of fused deposition modeling parts built with Acrylonitrile-butadiene-styrene (ABS) and ABS plus material is presented. ASTM D638-02a specimens were built with ABS and ABS plus and they were tested on a Schenck Trebel Co. tensile test machine at three different test speeds, equal, lower, and higher to the test speed required by the ASTM D638-02a standard. The experimental tensile strength results were compared and evaluated. The fracture surfaces of selected specimens were examined with a scanning electron microscope, to determine failure mode of the filament strands. It was found that, as the test speed increases, specimens develop higher tensile strength and have higher elastic modulus. Specimens tested in the highest speed of the experiment had on average about 10% higher elastic modulus and developed on average about 11% higher tensile strength.     

Alternating-laser excitation of single molecules

Single-molecule fluorescence spectroscopy addresses biological mechanisms and enables ultrasensitive diagnostics. We describe a new family of single-molecule fluorescence methods that uses alternating-laser excitation (ALEX) of diffusing or immobilized biomolecules to study their structure, interactions, and dynamics. This is accomplished using ratios that report on the distance between and the stoichiometry of fluorophores attached to the molecules of interest. The principle of alternation is compatible with several time scales, allowing monitoring of fast dynamics or simultaneous monitoring of a large number of individual molecules.     

Impact of surface state in probeless friction stir spot welding of an Al–Li alloy

ABSTRACT

Sheets of AA2198 alloy with various surface conditions were welded with probeless friction stir spot welding (P-FSSW). Results show that the oxide layer on the original lap-weld surface produces continuously distributed oxide impurities at the interface of the P-FSSWed joint with a large amount of voids. The visual flow at the interface provides a persuasive explanation of local preferential abrasion. Following surface grinding, local abrasion increases with surface roughness and results in the dispersion of voids and oxides, which contributes to the improvement of metallurgical connection. The corresponding mechanical strength of the P-FSSWed joints shows a relatively significant increase, while the fracture mode remains affected by the hook defect regardless of the surface state.     

Effects of microstructural asymmetries across friction stir welded AA2024 joints on mechanical properties

The effect of offset of the centre of a tensile specimen to the weldline on global tensile properties of friction stir welded AA2024 joints was investigated using experiments and numerical analysis. The size and geometry of these discrete zones, such as the central low hardness zone, the low hardness zone-I near the thermo-mechanically affected zone, the low hardness zone-II near the base metal and the base metal, were determined from a cross-sectional hardness map. Results show that tensile specimens with different area of the joint placed in the centre of the specimen do not affect the tensile strength and fracture path of a joint, strain is affected. Predictions based on local tensile properties follow well the measured global tensile behaviour.     

The effects of forging pressure and temperature field on residual stresses in linear friction welded Ti6Al4V joints

Linear friction welding (LFW), as a solid state joining process, has been developed to manufacture and repair blisks in aeroengines. The residual stresses after welding may greatly influence the performance of the welded components. In this paper, the distribution of residual stresses in Ti6Al4V joints after LFW was investigated with numerical simulations. The effects of applied forging pressure and temperature field at the end of the oscillating stages on the residual stresses within the joints were investigated. The results show that, the residual tensile stresses at the welded interface in the y-direction are the largest, while the largest compressive stresses being present at the flash root in the z-direction. Furthermore, the forging pressure and temperature field at the end of the oscillating stages strongly affect the magnitude of the residual stresses. The larger forging pressure produced lower residual stresses in the weld plane in all three directions (x-, y-, and z-directions). Larger variance, σ, which decides the Gaussian distribution of the temperature field, also yields lower residual stresses. There is good agreement between simulation results and experimental data.     

A Facile Method for Reversibly Linking a Recombinant Protein to DNA

A simple modification allows DNA to be linked to recombinant proteins. DNA functionalized with three nitrilotriacetic acid groups forms coordination complexes with nickel ions and the His₆‐tag of the recombinant protein (here, GFP). This noncovalent linkage is reversible, site‐specific and has a high (nanomolar) affinity.

     

3D Finite Element Analysis of the Effect of Process Parameters on Linear Friction Welding of Mild Steel

In this work, a 3D numerical model was developed to investigate the complicated thermo-mechanically coupled process of linear friction welding (LFW). The explicit-implicit alternate method was adopted for the first time to simulate LFW mild steel based on the ABAQUS software. To cope with the excessive element distortion, remeshing was conducted at certain calculation time with the help of the HYPERWORKS software. Results show that the interface temperature is quickly increased to near 900 °C within 1 s. With increasing the welding time, the interface temperature reaches a quasi-steady state of about 950 °C and the axial shortening rate keeps almost constant. A final unilateral axial shortening of 2.73 mm was obtained under the experiment condition, which corresponds well to the experiment. Moreover, the effects of processing parameters (oscillation frequency, oscillation amplitude, and friction pressure) on the joint temperature evolution and axial shortening were systematically examined and discussed. These three parameters could be integrated into one factor, i.e., heat input to the interface.     

Process parameter analysis of inertia friction welding nickel-based superalloy

A two-dimensional axisymmetric model for the inertia friction welding (IFW) of a nickel-based superalloy was developed. The influences from the axial pressure, initial rotational speed, and moment of inertia of the flywheel on the interface temperature and axial shortening were systemically examined. The analysis shows that the mechanical energy mainly depends on the initial rotational speed, and a relatively high axial pressure will increase conversion efficiency from mechanical energy to effective welding heat. The axial shortening is found to be approximately proportional to the square of initial rotational speed while logarithmical to the axial pressure. Based on this work, the weldability criteria for IFW nickel-based superalloy was established. Additionally, the approach for welding parameter optimization was performed considering the evolution of temperature profiles from various parameters. The results show that the axial pressure has a more obvious effect on the width of high-temperature zone than the rotational speed during the quick shortening stage.