System and method for in-situ testing of mechanical properties of materials in static and dynamic load spectra

A method for in-situ testing of mechanical properties of materials in static and dynamic load spectra, a stress-strain decoupling method for an Arcan biaxial clamping subsystem and a biaxial pre-tension loading subsystem, comprising:

• a central region and a gauge portion of a cruciform test piece are simplified to a unit body with uniform deformation;
• when calculating an actual stress and strain caused by each component of loads suffered by the cruciform test piece under a tension-shear plane stress state and a biaxial tension plane stress state, by means of principle of superposition, combined effects of a tension-shear load and a biaxial tension load on the stress and strain of the cruciform test piece are decoupled into a vector coupling superposition of a stress-strain constitutive relation under each single load;
• taking an elastic elongation, a plastic flow and a cross-section change of a material, in a target load acting direction, caused by other class of loads into consideration, a deformation behavior of the unit body of a simplified model in the target load acting direction is quantitatively described so as to obtain a relationship between the stress and strain under the target load and a known coupling load and a displacement,
• the decoupling method comprising:
• for a tension-shear composite stress state, in order to calculate an actual tensile strain and an actual shear strain of the cruciform test piece under an external load, which forms an acute angle to an axial direction of the cruciform test piece,
• establishing a simplified regular hexahedron model, wherein the simplified regular hexahedron model characterizes the gauge portion of the cruciform test piece, wherein an offset angle formed between an initial geometric axis of the regular hexahedron and a stretching direction is a known parameter, and a length, a width and a height of the regular hexahedron respectively correspond to a length, a width and a thickness of the gauge portion of the cruciform test piece;
• quantitatively calculating an angle between a geometric axis of a rhombohedron and the initial geometric axis of the regular hexahedron, wherein under the external load coaxial with the stretching direction, the regular hexahedron model is changed to the rhombohedron;
• and
• verifying, wherein an actual tensile stress and strain and a shear stress and strain of a cruciform test piece are directly collected and calculated by force sensors and displacement sensors, respectively, and then a respective tensile stress-strain curve and a respective shear stress-strain curve are decoupled, and then the decoupling method can be verified by three-dimensional strain analysis of a digital speckle measurement technique;
• for a biaxial tension mode, a central region of the cruciform test piece is stretched evenly under an action of plane stress, whereas a width of a parallel beam section gradually decreases in a load acting direction, a quantitative relationship between a deformation distribution and a load effect of the cruciform test piece is established by simulation analysis and image test method.