Design And Dynamic/Static Analysis Of An In Situ Combined Tension-torsion Testing Machine

The failure of materials when they are serving has already became abottleneck problem of restricting the development of national economy andindustry. The reasons for materials’ failure are lack of ability on testingmaterials’ serving mechanical properties and dim about materials deformationand damage mechanism.In this paper, careful analysis and research on current situation ofcombined tensile-torsion testing machine and in situ measuring technique isconducted. Commercial combined tension-torsion testing machine have no insitu observation function and in situ testing systems can only apply single load.In addition its load capacity is insufficient.In view of these problems, a testing machine that integrating in situobservation platform is designed. It can conduct quasi static tensile, tensilefatigue, quasi static torsion and quasi static combined tensile-torsion tests. Inother words it can measure materials’ serving mechanical properties and at thesame time it helps us to study materials deformation and damage mechanism. Itis made up of frame, tensile part, torsion part, jig part and observation platform,which adopts four columns and symmetric loading structure. Tensile part adoptshydraulic servo system and its design calculation is described. Torsion partadopts two-stage reducer that includes planetary gear and worm gear.Mechanical jig based on taper-lock clamping is put forward.In this paper, the equivalent models of testing machine’s joint surfaces arebuilt via virtual material method and spring element method. Thefrequency-response curves of joint surfces are obtained via modal testing andthe joint surfaces’ parameters are identified based on finite element simulationmethod. At the same time, the correction of equivalent models is validated.In this paper, dynamical models of testing machine and its parts are built.Via contrastive analysis of frame, it’s found that joint surfaces have vital influence on dynamic performance of testing machine. Since columns’ lateralstiffness is low, frame’s inherent frequencies are low, which leads to testingmachine’s inherent frequencies are low. Therefore, another task of this paper isto optimize the design of columns.The design of tensile part and torsion part meets the requirement. Theobservation platform’s inherent frequencies are low, leading to that testingmachine’s inherent frequencies of local vibration mode are low. This is becausethe stiffness of ball screw and ball guide joints is low.This paper investigates the displacement distribution of specimen when itconducts quasi static tensile tests.The zero displacement position of specimen isfounded, which helps us determine the proper position of pre-existing cracks.Modal testing is carried out to obtain the machine’s inherent frequencies.When joint surfaces are ignored, difference between simulation andexperimental results are obvious, even leading to some modes of vibration’s loss.When joint surfaces are considered, the simulation’s error ranges from0.99%to17.6%, which verifies the model’s reliability.