| As one of the three pillars of contemporary civilization,material is the material basis for human survival and development.Due to lack of performance support,major accident caused by material failure often occurs and leads to great loss to safety of life and property.In actual use,all kinds of materials and their products are always affected simultaneously by multiple complex loads.Traditional single loads mechanic testing technology could not be used to accurately evaluate the mechanic performance of material under complex loads.This problem is widely concerned in engineering circles.In recent years,with the development of science and technology,in-situ mechanic performance test technology for material has emerged.Various micro imaging devices are applied in mechanic performance test of material.Imaging devices are used to observe the micro deformation,damage and failure of test-piece in real time.By such mechanic test method,the rules of material deformation and damage under external load could be revealed,and the problem due to component size equivalence could be avoided.It is beneficial for studying the real micro mechanic action and the mechanism of deformation and damage of material and its products in use.Combined load test modes with multiple loads are rarely involved in current in-situ mechanic test device.Therefore,in this paper,a biaxial tension-bending complex load test device for in-situ test was designed.The stress state affected by tensile load and bending load in multiple directions was simulated.Thus,the mechanic performance of material in actual use could be tested more accurately.It is important for predicting and analyzing its life and reliability so as to guarantee its performance.In this paper,based on theoretical analysis,mechanic test device and its control system were developed for micro mechanic performance of cross-shaped test-piece under biaxial tension and bending combined loads.Simulation analysis was conducted for virtual prototype of test device to guarantee rationality of device design.The performance of test device was systemically tested and analyzed.Meanwhile,this test device was used in a series of experiments.The contents of this paper include:In this paper,based on systemic theoretical research on traditional tension and bending theory,theoretical formulas under three states,uniaxial tensile and bending combined load,biaxial tensile combined load as well as biaxial tensile and bending combined load,were proposed and verified by subsequent test data.For the error between test result and actual value of test device,some specific modified algorithms were proposed according to the error caused by test-piece clamping and deformation,including horizontal plane angle deviation modified algorithm,test-piece clamping end height deviation modified algorithm,deformation of non-gauge length part modified algorithm,biaxial tensile deformation modified algorithm as well as biaxial tensile and bending deformation modified algorithm.The test device after calibration was used to test and verified the accuracy of modified algorithm.Biaxial tensile-bending load device was designed and analyzed.The research on the functional module design of biaxial tensile load unit,bending unit and test-piece clamping unit was focused.Advanced simulation of UG software was used to conduct finite element simulation analysis of static and dynamic characteristics of key spare parts and the whole device so as to guarantee design rationality.In order to guarantee accuracy of mechanical device assembling,assembling adjustment of clamping component of test-piece under three-dimensional test was conducted to guarantee that test-piece clamping is good to neutral and bending direction is consistent.Force sensor and displacement sensor were calibrated and assembled into mechanical structure of test device so that control system and mechanical device was integrated.The development and online debugging of control interface of upper computer were finished.Through debugging,control interface was optimized and gain parameters were adjusted.In this paper,comparative trail with commercial device was conducted.The test-pieces of same material and size were tested on commercial device and the test device designed in this paper,respectively.The data of comparative trail were used to verify the reliability and stability of the test device designed in this paper.Pure aluminum material and red copper material were used to conduct uniaxial tensile comparative trail,uniaxial tensile repeated trail and bending repeated trail,respectively.Trail data proved that the test device designed in this paper has high accuracy in measurement and repeatability.The mechanic performances under biaxial tension and bending load of typical metal materials,aluminum alloy 6061 and titanium alloy,were studied.Biaxial tension test of aluminum alloy 6061 was conducted under different pre-bending loads.It was found as pre-bending force increased,the elastic deformation stage on curve gradually shortened.The force needed for elastic deformation increased,and the slope of elastic deformation stage curve slightly increased.After pre-bending force was loaded,the ability of material to resist elastic deformation increased.Bigger load was needed for elastic deformation than which without pre-bending force.Thus,anti-tension strength was generated ahead of time.Uniaxial test and biaxial test of titanium alloy test-piece under different tensile speeds were conducted.FEI Quanta 200 SEM was used to conduct fracture analysis.It was shown that tensile speed could positively influence anti-tensile strength.If tensile speed was properly improved,more ideal anti-tensile strength could be obtained.Fracture analysis of test-piece indicated that as tensile speed increased,dimple size gradually reduced.It meant that the plasticity of material would reduce as tensile speed increases.In summary,the research in this paper is not only the design and development of micro mechanic test device,but also the further study on mechanic performance test under combined load.The development method of micro mechanic combined load test device and related theories could be used as reference for the development of micro mechanic performance test technology and device. |
