Measurement of residual stresses in austenitic stainless steel weld joints using ultrasonic technique

Abstract

A methodology has been developed using a non-destructive ultrasonic technique for measuring surface/subsurface residual stresses in 7 mm thick AISI type 316LN stainless steel weld joints made by activated tungsten inert gas and multipass tungsten inert gas welding processes. Measurement of residual stresses using an ultrasonic technique is based on the effect of stresses on the propagation velocity of elastic waves. Critically refracted longitudinal L _CR wave mode was employed and accurate transit time measurements were made across the weld joints. Quantitative values of the longitudinal residual stresses across the weld joints were estimated from the measured transit times and predetermined value of acoustoelastic constant for AISI type 316LN stainless steel. The nature of the residual stress profiles and their variations across the two types of weld joints were compared and interpreted.     

New structure of automatic torch and new approach for controlling drop transfer in rotating spray welding arc

Abstract

Using computer aided design/computer aided manufacturing technology, an automatic welding system is designed and manufactured for high current, high speed, and high deposition metal arc active gas (MAG) welding. The welding torch structure is evaluated and optimised via the finite element method and practical welding technology experiments. Finally, the process of high deposition MAG welding is investigated, and it is highlighted that on application of a longitudinal magnetic field to the high deposition MAG welding process, a steady metal transfer and drop deposition condition can be achieved, which is suited to the demands of high current, high speed welding technology.     

Material response of GMA welded 1 mm thick DP600 overlap joints

Abstract

In a previously published model, gas metal arc welding of 1 mm thick DP600 overlap joints is validated for the transient temperature distribution, the welding distortion and longitudinal residual stresses. Tensile tests have been simulated and performed experimentally. Validations were performed for two clamping cases: an immediate release of the clamps after welding and a release of the clamps after cooling to room temperature. There is good agreement between experiments and simulations. It has been found that the temperature distribution, longitudinal stresses and welding distortions are dependent on the clamping conditions. To explain the effect of the clamping time, a bar model is proposed. It is shown that longer clamping times increase plastic deformation and hence reduce residual stresses and buckling distortion. Additionally for an overlap joint, it has been found that the longitudinal residual stresses are affected significantly by the sample's geometry.     

Study on surface- and mechanical fiber characteristics and their effect on epoxy composite properties tuned by continuous anodic carbon fiber oxidation

Continuous anodic oxidation was employed to alter the surface chemical properties of carbon fibers. As expected, the wetting behavior by water improved and that of non-polar liquid diiodomethane deteriorated. The calculated surface tensions mirror the changes in the physicochemical surface properties. The zeta (ζ)-potential measurements performed also reflect changes in the surface chemistry of the investigated carbon fibers. A correlation between the measured ζ-potentials and the wetting behavior of water on anodically oxidized carbon fibers was found. The influence of anodic carbon fiber oxidation on the epoxy composite properties was studied by a modified axial tensile test, which allows additionally the measurement of the so-called 'notching force' as a measure of the interfacial composite properties. Common model-composite samples were used to check the reliability of this test. The determined 'notching force' as a measure of adhesion correlates with the increased polar component of the fiber surface tension.     

28—THE EFFECT OF STEAMING ON THE LONGITUDINAL STABILITY OF WOOL YARN

An account is given of an investigation of the effectiveness of steaming on the longitudinal stabilization of wool yarn. Specially prepared worsted yarns were used to study the effects of initial regain and of time and temperature of steaming.

Of the several different mechanisms proposed for the longitudinal stabilization of yarn by steaming, only permanent setting is demonstrated directly, and the effects of temperature, initial regain, and time of treatment are established. Two threshold values were observed below which no permanent setting took place—an Initial-regain threshold of 7–8% and a temperature threshold of about 88°C. It is considered possible that the threshold temperature is a function of the particular release treatment used and that it would increase with increasing severity of the conditions of release.

The contribution of permanent setting to the over-all longitudinal stabilization was apparently small, but this may have been a result of using a rather severe release treatment.     

Robust Adaptive Stabilization of Skid Steer Wheeled Mobile Robots Considering Slipping Effects

This paper represents the posture stabilization of a skid steer wheeled mobile robot (SSWMR). Although in mobile robots lateral skidding of the wheels occurs when turning at high speed, wheels of a SSWMR laterally skid in every rotational maneuver even at low speeds. Also, longitudinal slipping for wheeled mobile robots with pneumatic tires is inevitable due to tire deformation. In order to compensate for the effects of tire slippage and parameter uncertainties, an adaptive torque controller is developed based on a tunable dynamic oscillator. The globally uniformly ultimately bounded stability of the system to an arbitrarily small neighborhood of the origin is proved. The internal dynamics stability of the system is guaranteed employing a supervisory fuzzy logic-based controller. To demonstrate the performance of the proposed controller, modeling of a SSWMR was implemented through automatic dynamic analysis of mechanical systems (ADAMS).