Residual stress analyzer is a kind of physical property testing instrument used in the field of mechanics, mechanical engineering, water engineering, aviation, aerospace science, and technology.
X-ray residual stress analysis is one of the few non-destructive methods in surface residual stress determination technology, which is based on the variation of the grain surface spacing of the material or product to determine the stress, and is one of the most widely studied, in-depth, and mature residual stress analysis and detection methods, making it possible to measure the real field and irregular shape samples.
Mechanical processing fieldResidual stress analysis can be used to measure residual stresses in machine tools, welding, casting, forging, cracking and other components.
Metallurgical industryThe residual stress analyzer measures residual stresses in hot pressing, cold pressing, iron making, steel making, casting and other industrial production components.
Various parts manufacturingStress X-Ray can also be used to measure residual stress in industrial products such as power station turbine manufacturing, engine manufacturing, oil cylinders, pressure vessels, pipes, ceramics, assemblies, bolts, springs, gears, bearings, rollers, crankshafts, piston pins, universal joints, machine shafts, blades, tools, etc.
Surface modification treatment: measurement of residual stress in components after treatment with nitriding, carburizing, carbonitriding, quenching, hardening treatment, shot blasting, vibration impact, extrusion, rolling, diamond lapping, cutting, grinding, turning (milling), mechanical polishing, electropolishing and other processes.
Infrastructure construction field(1) Marine field: residual stress analysis can measure the residual stress in equipment and facilities of ships, marine, petroleum, chemical, lifting, transportation, ports, and other fields.
(2) Energy field: Measure the residual stress of equipment and facilities in the nuclear industry, electric power (water conservancy and hydropower, thermoelectricity and nuclear power), water conservancy engineering, natural gas engineering, and other fields.
(3) Infrastructure engineering field: Measure the residual stress of materials, components, and other related equipment and facilities used in the fields of excavation, bridge, automobile, railroad, aerospace, transportation, steel structure, and other engineering fields. 6. Defense and military industry field: Measure the residual stress of military products such as weapons and equipment, heavy equipment, etc.
Faster: The residual stress instrument's 2D detector acquires the complete Debye ring in a single acquisition, and the measurement can be completed in a single incidence at a single angle, with an average of about 60 seconds for the whole process.
More accurate: The residual stress instrument can obtain 500 data points for residual stress data fitting in one measurement, making the results more accurate.
Easier: no goniometer is required for stress measurement, a single angle is all that is needed for complex shapes and confined spaces.
More convenient: stress measurement tool with high measurement accuracy, no need for cooling water, no external power supply for fieldwork.
More powerful: X-Ray diffraction machine with regional stress distribution measurement imaging function, grain size, material structure, residual austenite analysis, and other functions.
At present, the testing methods of
residual stress analyzers can be divided into lossy stress measurement method and non-destructive stress measurement method.
Lossy stress measurement methodBlind hole methodThe blind hole method was proposed by German scholar MatharJ in 1934 and has been developed to a more mature level. The principle is to apply a strain flower on the surface of the measured workpiece and punch a hole in the workpiece, the stress around the hole is relaxed, and a new stress/strain field distribution J is formed; by calibrating the strain release coefficients A and B, the original residual stress and strain of the workpiece can be deduced based on the principle of elastic mechanics.
Indentation methodThe indentation method is based on the principle of hardness testing and is a non-destructive or micro-destructive stress measurement technique. Its principle is that under local load, the existence of internal stress components will produce displacement and strain due to stress superposition, measuring the displacement △Z and strain △ε, the original surface residual stress of the component can be deduced (the general indentation diameter and depth of 1.2mm × 0.2mmm).
The indentation method requires attention to the following issues: control of the indentation test zone and the surrounding plastic strain zone; if the plastic strain zone completely overlaps with the test zone, the measurement results are affected, and if the plastic zone is completely isolated, the test sensitivity is reduced; establishment of the relationship between the indentation strain increment and the residual stress as a function of the residual stress; calibration experiments and simulation calculations to establish the quantitative relationship between the strain increment and the material properties, and calculation simulations instead of calibration The calibration experiments and simulations are used to establish the quantitative relationship between strain increment and material properties.
Cutting methodThe cutting method is to cut the metal along the deformation plane, accurately measure the deformation profile of the cutting surface, and then fit the test profile, the fitting results as the boundary conditions of the finite element model for elastic calculations obtained the internal vertical cutting plane stress distribution, you can get the distribution trend and characteristics of the cutting surface stress, suitable for qualitative measurement of residual stress in large pieces of material.
The cutting method has high measurement accuracy due to the complete release of residual stresses by destroying the structural member. The initial residual stress within the sample can be obtained indirectly by measuring the released stress using a resistance strain gauge.
Non-destructive stress measurement methodUltrasonic methodUltrasonic method is to measure the stress by the propagation characteristics of ultrasonic waves inside the material, i.e., the tensile stress causes the sound waves to propagate longer and slower, and the compressive stress, on the contrary, uses the acoustic birefringence effect caused by stress to measure the stress. The change in stress causes a very small change in sound velocity, with 100 MPa causing only about 0.1% change in sound velocity. The critical refraction longitudinal wave (LCR) is the refraction longitudinal wave when the refraction angle is 90 degrees, which is the most sensitive to stress and should be the most widely used.
Magnetic methodThere are two magnetic methods currently applied: the magnetic noise method and the magnetic strain method. The basic principle of the magnetic noise method of measurement is to use the magnetostrictive effect of ferromagnetic materials. Stress causes a change in the domain wall spacing of the ferromagnetic material, which affects the strength of the Barkhausen (magnetic induction B with a discontinuous jump in magnetic field strength H) emission signal. The magnetic strain method uses the magnetic anisotropy of the material for stress measurements. When stress exists, the permeability changes accordingly, and the magnetic resistance of the magnetic circuit between the sensor and the material surface changes during the measurement, which in turn leads to a change in the magnetic flux of the magnetic circuit.
The magnetic strain method cannot measure large residual stresses (greater than 300 MPa), where the relationship between stress and magnetic permeability is non-linear. The magnetic method is compact, simple and fast, but it is difficult to directly measure the stress value at multiple points, and only the quantitative relationship between the difference in principal stress at a single point and the magnetic measurement parameters can be measured.
The type of material tested by this method is limited to the determination of stress in ferromagnetic materials such as steel and iron; in addition, like the ultrasonic method, although the magnetic method can measure the internal stress of the material, the measurement results are more disturbed by the microstructure of the material (voids, voids, cracks, etc.). After the industry experts Huang Haihong et al. proposed a metal magnetic memory detection technology, which can quickly detect the dangerous area of the component and can indicate the stress concentration through the magnetic memory signal gradient value.
X-ray diffraction methodX-ray method was proposed by Russian scholars in 1929, and after years of development, the theoretical and practical measurement methods are more mature, and it is the most widely used non-destructive residual stress testing method.
The X-ray diffraction method for measuring residual stress is based on the theory of X-ray diffraction. When a beam of X-rays with wavelength λ is irradiated on the surface of a crystal, a wave peak of reflected X-rays will be received at a specific angle (2θ), which is the X-rays diffraction phenomenon. The diffraction angle 2θ follows the well-known Bragg's law: 2dsinƟ=nλ. between the wavelength λ of the X-rays and the diffracting crystal surface spacing d.
Neutron diffraction methodThe neutron diffraction method is similar to the x-ray diffraction method in principle, while the neutron penetration depth is larger, thus allowing the detection of residual stress distribution inside large pieces of material (on the order of centimeters).
The accuracy of the neutron diffraction peak position is influenced by the diffraction intensity, which depends mainly on the test time under certain conditions such as reactor power, diffraction crystal plane and canonical volume.
Neutron diffraction measurement of residual stresses is time-consuming and expensive, usually requires a large standard volume of sample (10 mm3) and poor spatial resolution, and is not useful for the measurement of residual stresses in the surface layer of the material (>100 um and above region ).
