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The measurement of hydrodynamic loads on submerged bodies is one of the principal uses of water tunnels. Due to the limitations of the water tunnel, an accurate force balance is necessary. This paper describes the design, fabrication and calibration of a new six-component force moment balance system for measuring the forces and moments acting on the model, in static and dynamic water tunnel testing. A balanced team performed many areas for designing balance system such as structural design, balance technology, design of calibration mechanism, balance calibration etc. A six-component balance, ability to measure the three elements of force and three components of moment simultaneously and instantly on cavitating and non- cavitating models in a water tunnel. The concept used in the balance design is the bending beam and the strain gage principle. The electrical signals are proportional to the forces applied to the model. By considering the relationship between the applied force and the balance’s output signal and by using the calibration models, the forces and moments exerted on the model in the water tunnel can measure directly. For calibrate multi component balance, a new six-degree of freedom calibration rig designed and constructed. The system is designed based on applicability of formal experimental design techniques, using gravity for balance loading and balance position and alignment relative to gravity. The six-component balance was calibrated by this rig. The standard error between the measured values and the values obtained from calibration model is less than 0.1 percent of maximum loading was achieved.

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Cold working a hole decreases tendency of fatigue crack near the hole to initiate or growth. It is due to creation some compressive tangential residual stresses around the hole. Determination of mentioned residual stresses with a non-destructive, simple and non-expensive method is the key step in design process of holed components. In this article, residual stresses have been determined by mounting some strain gages around the hole and in fact surface strains during cold working process have been introduced as a feature for residual stress field. Delineation the numbers of needed strain gages and also proper place for mounting them around the cold worked hole is the main object of this research. Results have a good agreement with test result of cold working on specimens made of Al2024. According to the results, mounting two strain gages at same radius in opposite side of hole edge; which one in radial and another in tangentially direction; is needed for determining the residual stress field. Also, strain gages should be mounted in elastic zone. Mounting the gages in plastic zone led to have errors and unreliable results.

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In this paper, the numerical distribution of residual stresses in the girth weld were determined in two (hoop an axial) direction. Two API X70 steel pipes of 56 inch outside diameter were girth welded first. Hole drilling strain gage test were conducted for strain measurement on the external surface of the pipes. The values of residual stresses were determined then from strain data using ASTM 837 standard. The values of residual stresses were determined. Next, distribution of residual stresses were assessed using spline and approximating polynomials. The well-behaved spline and polynomials, confirm the accuracy of residual stress results from experiment. The result showed lower-order polynomials have more suitable behavior in residual stress distribution. Noting to impossibility of using semi-destructive hole drilling strain gage test in project’s real situations, we can make use of these curves in assessing and estimating residual stresses distribution of similar welding. The most stable polynomial estimation curves for evaluating hoop and axial residual stress distribution are respectively third and second order. The closeness and uniformity of axial residual stress distribution curve compared to the hoop residual stress distribution curve is representative of more balanced behavior of these stresses distribution.

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In this paper, the analysis of variance (ANOVA) of weld residual stress distribution (using the hole drilling strain gage method according to ASTM 837 standard) was investigated (in the hoop and axial direction of the 56-inch gas transmission). The results of ANOVA show that the best distribution curve of residual stress is the third order function (3 degree of freedom) in the distribution diagram of hoop and axial residual stresses. In this order, the p value of the hoop and axial residual stress is 0.044 and 0.001, respectively. This indicates the high reliability of the third order function. Also, the value of F and coefficient of determination of this order has an appropriate value. In addition, due to the high p value and low reliability, the 5-order approximation function is not a suitable residual stress distribution curve compared to the third order function. Order approximation functions (2 and 4) have lower reliability (higher p value) and lower F value than odd order (3 and 5). Despite having the highest freedom with the highest p (lowest reliability), the lowest F, and the lowest coefficient of determination, the second-order function, is the most inappropriate approximation function. Despite the existence of residual stress with respect to the zero experimental residual stress compared to the approximation function, the use of strain test in points far from the weld one and the base metal is not essential.