Research On Weldable Method And Device For Stress Measurement In Underwater

The electrical resistance strain measurement is an important mean for solving problems of engineering mechanics, outdoor strain measurements are often involved in humid environment, so that the treatment for moisturing is difficult and cockamamie. Therefore accomplishing the pre-work of strain gauge for adhering to stainless steel film and waterproof protecting in laboratory, then weld to the structures in damp environment for strain measurement, this way can improve the efficiency and reduce the cost of strain measurement.Basing on the theory of material mechanics and elastic theory, this paper presents the weldable method and device for stress measurement in underwater associated with the verification from the FEM(finite element method) calculation and experimental studies. The main conclusion is given as follows:(1) The stress and strain distribute on the surface of equal strength beam if its load point shift toward the clamped end as the result of processing are nonlinear changing. The stress σ and the strain σ are linear changing approximately beside the clamped tip; otherwise they are both following in higher order term.(2) The modified formula is available to correct the value of strain which is measured by the way of welding steel film that thickness is from0.05to0.20mm to the structure under the bending load. When the experiment error is allowable to laboratory apparatus beside both the MOE(modulus of elasticity) of steel film and structure are similar, the value of strain is unnecessary to correct; the thickness in0.10mm is the best choice. This way can be use in damp environment for strain measurement after waterproof protecting.(3) The modified formula presented in this paper is much accuracy to correct the value of strain on the condition that the thickness of steel film is from0.05to0.10mm under the unidimensional stretching load. The thickness in0.10mm is more available to improve maneuverability and reduce experime-ntal error. This method can satisfy the conditions of strain measurement in damp environment.(4) The formula about the relation of true strain and measured value under the two-dimensional stretching load is expressed on the basis of the unidimensional load, verification of data from FEM calculation shows that this formula is wonderful when the thickness of the steel is less than0.10mm.(5) The weldable device for stress measurement in underwater is manufactured; both FEM calculation and experimental data show the linear relation with measured value from this device and the true strain. The device: good waterproof performance, simple operation, low cost, can be applied conveniently in engineering.