To study the creep property of salt rock, uniaxial compression creep tests on salt rock specimens were carried out. The test results indicate that there is no steady creep of the salt rock used in ...

Creep properties and damage constitutive model of salt rock under uniaxial compression

Pre-stressed bolted joints are widely used in civil structures and industries. The tightening force of a bolt is crucial to the reliability of the joint connection. Loosening or over-tightening of a bolt may lead to connectors slipping or bolt strength failure, which are both harmful to the main structure. In most practical cases it is extremely difficult, even impossible, to install the bolts to ensure there is a precise tension force during the construction phase. Furthermore, it is inevitable that the bolts will loosen due to long-term usage under high stress. The identification of bolt tension is therefore of great significance for monitoring the health of existing structures. This paper reviews state-of-the-art research on bolt tightening force measurement and loosening detection, including fundamental theories, algorithms, experimental set-ups, and practical applications. In general, methods based on the acoustoelastic principle are capable of calculating the value of bolt axial stress if both the time of incident wave and reflected wave can be clearly recognized. The relevant commercial instrument has been developed and its algorithm will be briefly introduced. Methods based on contact dynamic phenomena such as wave energy attenuation, high-order harmonics, sidebands, and impedance, are able to correlate interface stiffness and the clamping force of bolted joints with respective dynamic indicators. Therefore, they are able to detect or quantify bolt tightness. The related technologies will be reviewed in detail. Potential challenges and research trends will also be discussed.

A Review of Bolt Tightening Force Measurement and Loosening Detection

Triaxial rheological property of sandstone under low confining pressure

To address the difficulty in testing and calibrating the stress gradient in the depth direction of mechanical components, a new technology of nondestructive testing and characterization of the residual stress gradient field by ultrasonic method is proposed based on acoustoelasticity theory. By carrying out theoretical analysis, the sensitivity coefficients of different types of ultrasonic are obtained by taking the low carbon steel(12%C) as a research object. By fixing the interval distance between sending and receiving transducers, the mathematical expressions of the change of stress and the variation of time are established. To design one sending-one receiving and oblique incidence ultrasonic detection probes, according to Snell law, the critically refracted longitudinal wave (LCR wave) is excited at a certain depth of the fixed distance of the tested components. Then, the relationship between the depth of LCR wave detection and the center frequency of the probe in Q235 steel is obtained through experimental study. To detect the stress gradient in the depth direction, a stress gradient LCR wave detection model is established, through which the stress gradient formula is derived by the relationship between center frequency and detecting depth. A C-shaped stress specimen of Q235 steel is designed to conduct stress loading tests, and the stress is measured with the five group probes at different center frequencies. The accuracy of ultrasonic testing is verified by X-ray stress analyzer. The stress value of each specific depth is calculated using the stress gradient formula. Accordingly, the ultrasonic characterization of residual stress field is realized. Characterization results show that the stress gradient distribution is consistent with the simulation in ANSYS. The new technology can be widely applied in the detection of the residual stress gradient field caused by mechanical processing, such as welding and shot peening.

Nondestructive testing and characterization of residual stress field using an ultrasonic method

Nondestructive Testing Residual Stress Using Ultrasonic Critical Refracted Longitudinal Wave

Based on the acoustoelasticity theory, a certain relationship exists between ultrasonic velocity and stress. By combining shear and longitudinal waves, this paper provides a nondestructive method of evaluating axial stress in a tightened bolt. For measuring the bolt axial stress in different situations, such as under low or high loads, this paper provides guidelines for calculating the stress for a given load factor. Experimental and calculated results were compared for three bolt test samples: an austenitic stainless steel bolt (A2-70) and low-carbon steel 4.8 and 8.8 bolts. On average, the experimental results were in good agreement with those obtained through calculations, thus providing a nondestructive method for bolt stress measurements.

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Characteristic Evaluation on Bolt Stress by Ultrasonic Nondestructive Methods

The invention relates to a curved-surface steel plate residual stress ultrasonic detection transceiver device. The device comprises an organic glass wedge, an ultrasonic transducer, and a magnetic base. A sensor device has a one-transmitting and one-receiving structure. Two devices adopt the magnetic base for ensuring the close contact and coupling of the sensor and a test sample. Because of the influence of curvature, incidence angles of point of a sound beam are different. According to the invention, the problems of organic glass curvature and ultrasonic incident angle are explained during a design process. The design idea provided by the invention is innovative. With the device provided by the invention, a difficulty of pipe stress detection is well solved, and a good application prospect is provided.

Curved-surface steel plate residual stress ultrasonic detection transceiver device

The invention relates to an ultrasonic non-destructive testing method for circumferential and axial residual stresses of inner and outer roller paths of a roller bearing. Ultrasonic longitudinal waves form critical refraction longitudinal waves in the inner and outer roller paths of the roller bearing through primary waveform conversion; time spent on that the critical refraction longitudinal waves propagate in the inner and outer roller paths of the roller bearing is measured; the mean circumferential and axial residual stresses of the inner and outer roller paths of the corresponding roller bearing can be calculated according to an acoustic elasticity theory. Furthermore, the distribution of the circumferential and axial residual stresses of the inner and outer roller paths of the roller bearing under different depths further can be measured by changing the frequency of the ultrasonic longitudinal waves. With the adoption of the ultrasonic non-destructive testing method provided by the invention, the problem of rapidly, conveniently and accurately detecting the distribution of the residual stresses of the inner roller and outer roller of the roller bearing can be effectively solved. The ultrasonic non-destructive testing method is widely applied to bearing production, repairing and maintenance sites, is a novel method of detecting the distribution of the residual stresses of a curve component within a narrow space, and has a very wide application range.

Ultrasonic non-destructive testing method for residual stress of inner and outer roller paths of roller bearing

The invention relates to a contact type ultrasonic non-destructive testing straight-line automatic scanning device. The device is mainly used for automatically detecting a straight-line welding line defect and welding residual stress. A magnetic type base can be used for conveniently adsorbing a detection device on a welding line region to be detected; a transverse beam of the detection device is formed by a motor and a straight-line guide rail; the motor drives a slide block for mounting a detection sensor to move along the straight-line guide rail; the sensor can be a residual stress detection sensor, a TOFD (Time Of Flight Diffraction) detection sensor and a surface defect detection sensor; and detected position information is recorded and fed back by a photoelectric encoder. The device can be applicable to automatic detection on the welding line region of a plate type welding component, can realize the automatic detection on a welding line of a curve-surface welding component including a pipeline and the like, and improves the detection efficiency.

Contact type ultrasonic non-destructive testing straight-line automatic scanning device

The invention relates to a device for detecting residual stress close to surfaces of metal materials The device stimulates a critical-refraction longitudinal wave and calculates a stress value according to an acoustic elasticity theory According to the invention, by reducing contact area between a wedge and a part to be measured, the affect of plate surface distortion to a measurement result can be effectively eliminated; the affect caused by temperature difference can be eliminated by temperature compensation; and therefore, the system is adaptable to tests in more terrible field environments The system is higher in integration degree, small and exquisite in appearance and convenient to carry

Li Xiao

Papers

Characteristic Evaluation on Bolt Stress by Ultrasonic Nondestructive Methods

Curved-surface steel plate residual stress ultrasonic detection transceiver device

Ultrasonic non-destructive testing method for residual stress of inner and outer roller paths of roller bearing

Contact type ultrasonic non-destructive testing straight-line automatic scanning device

Device for detecting residual stress close to surfaces of metal materials