Analysis of Optimal Roll Tensioning for Circular Saw Stability

When a circular saw is used to cut wood, a substantial and increasingly important fraction of the raw material is wasted because of the excessive width of the sawcut. The process of "roll tensioning" is studied here, whereby sawblade thickness, and hence material loss, can be significantly reduced while still maintaining sawblade stability. A theoretical model is developed that accurately describes the localized plastic deformation that takes place during roll tensioning, the associated residual stresses, and the resulting changes in sawblade natural frequencies. Experimental measurements of the residual stresses and natural frequencies confirm the theoretical predictions. The mathematical model allows reliable prediction of optimal tensioning conditions for any given saw operating state and development of automated control of the tensioning process. An example is presented in which the thickness of an optimally tensioned circular sawblade is 33% smaller than the thickness of an untensioned sawblade of equivalent transverse stability

Control of welding residual stress for dissimilar laser welded materials

The most common problem of welding dissimilar metals (DMWs) with respect to residual stresses is the differences in the coefficient of thermal expansion and heat conductivity of the two welded metals. In the present work, a CO2 continuous laser welding process was successfully applied and optimized for joining a dissimilar AISI 316 stainless steel and low carbon steel plates. The Taguchi approach with three factors (selected welding parameters) at five levels each (L3-25) was applied to find out the optimum levels of welding speed, laser power and focal position for CO2 keyhole laser welding of dissimilar butt weld. The responses outputs were the residual stresses at different depth in the heat affected zone (HAZ). The Hole-Drilling Method technique was applied to measure the residual stress of dissimilar welded components. The results were analysed using analysis of variances (ANOVA) and signal-to-noise ratios (S/N) for an effective parameters combination. Statistical models were developed to describe the influence of the input parameters on the residual stress at different specimen levels; to predict there value within the limits of the variables under investigation. The result indicates that the developed models can predict the responses satisfactorily

Why Is It So Challenging to Measure Residual Stresses ?

BACKGROUND: Residual stresses have a “hidden” character because they exist in a material without the presence of any external loads. They cannot easily be added or subtracted in a quantified manner, as is done when measuring applied stresses, and so are much more challenging to measure. OBJECTIVE: The objective here is to identify and describe the various features that make residual stress measurement methods challenging and to consider the ways that these challenges can be addressed in practice. METHODS: Various of the most common residual stress measurements methods are considered and the challenges associated with them are identified and classified. RESULTS: Five major challenges for residual stress measurements, and the approaches used for their resolution, are identified. CONCLUSIONS: Despite the various challenges that need to be overcome, residual stress measurements can be successfully undertaken in practice. The most significant feature for success is a highly skilled and knowledge practitioner

Prediction of residual stresses in girth welded pipes using an artificial neural network approach

Management of operating nuclear power plants greatly relies on structural integrity assessments for safety critical pressure vessels and piping components. In the present work, residual stress profiles of girth welded austenitic stainless steel pipes are characterised using an artificial neural network approach. The network has been trained using residual stress data acquired from experimental measurements found in literature. The neural network predictions are validated using experimental measurements undertaken using neutron diffraction and the contour method. The approach can be used to predict through-wall distribution of residual stresses over a wide range of pipe geometries and welding parameters thereby finding potential applications in structural integrity assessment of austenitic stainless steel girth welds

Methods of measuring residual stresses in components

Residual stresses occur in many manufactured structures and components. Large number of investigations have been carried out to study this phenomenon and its effect on the mechanical characteristics of these components. Over the years, different methods have been developed to measure residual stress for different types of components in order to obtain reliable assessment. The various specific methods have evolved over several decades and their practical applications have greatly benefited from the development of complementary technologies, notably in material cutting, full-field deformation measurement techniques, numerical methods and computing power. These complementary technologies have stimulated advances not only in measurement accuracy and reliability, but also in range of application; much greater detail in residual stresses measurement is now available. This paper aims to classify the different residual stresses measurement methods and to provide an overview of some of the recent advances in this area to help researchers on selecting their techniques among destructive, semi destructive and non destructive techniques depends on their application and the availabilities of those techniques. For each method scope, physical limitation, advantages and disadvantages are summarized. In the end this paper indicates some promising directions for future developments

Residual stress measurement round robin on an electron beam welded joint between austenitic stainless steel 316L(N) and ferritic steel P91

This paper is a research output of DMW-Creep project which is part of a national UK programme through the RCUK Energy programme and India's Department of Atomic Energy. The research is focussed on understanding the characteristics of welded joints between austenitic stainless steel and ferritic steel that are widely used in many nuclear power generating plants and petrochemical industries as well as conventional coal and gas-fired power systems. The members of the DMW-Creep project have under- taken parallel round robin activities measuring the residual stresses generated by a dissimilar metal weld (DMW) between AISI 316L(N) austenitic stainless steel and P91 ferritic-martensitic steel. Electron beam (EB) welding was employed to produce a single bead weld on a plate specimen and an additional smoothing pass (known cosmetic pass) was then introduced using a defocused beam. The welding re- sidual stresses have been measured by five experimental methods including (I) neutron diffraction (ND), (II) X-Ray diffraction (XRD), (III) contour method (CM), (IV) incremental deep hole drilling (iDHD) and (V) incremental centre hole drilling (iCHD). The round robin measurements of weld residual stresses are compared in order to characterise surface and sub-surface residual stresses comprehensively

Analysis of Residual Stresses in Laser-Shock-Peened and Shot-Peened Marine Steel Welds

Laser peening is now the preferred method of surface treatment in many applications. The magnitude and depth of the compressive residual stress induced by laser peening can be influenced strongly by the number of peen layers (the number of laser hits at each point) and by processing conditions including the use of a protective ablative layer. In this study, residual stresses have been characterized in laser and shot-peened marine butt welds with a particular focus at the fatigue crack initiation location at the weld toe. X-ray diffraction, synchrotron X-ray diffraction, incremental center-hole drilling, and the contour method were used for determination of residual stress. Results showed that the use of ablative tape increased the surface compressive stress, and the depth of compressive stress increased with an increase in number of peening layers. A key result is that variation of residual stress profile across laser peen spots was seen, and the residual stress magnitude varies between the center and edges of the spots

Mechanical analysis of end-to-end silk-sutured anastomosis for robot-assisted surgery

Background Robot-assisted anastomosis holds great promise for the future. To secure surgery quality, some key process factors, such as the force arrangement of sutures, should be provided because of the lack of haptic feedback in robotics systems Methods A model of anastomosis is presented to establish the mechanical relationship between vessel and sutures. Stress distribution of the vessel loaded by the suture was then achieved through finite-element simulations, based on the material property test results. Further, experiments were performed to validate the reliability of the FEM simulation of the anastomosis process. Results To avoid blood osmosis, the allowable lower limit of the suture tension was 0.05 N. To keep the tissue free from injury, the allowable upper limit of tension on the suture was 0.4 N. Conclusions The study provided meaningful results for directing the robot-assisted anastomosis procedure and design of the surgical tools. Copyright © 2009 John Wiley & Sons, Ltd.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/64523/1/276_ftp.pd