Ultrasonic testing of axial stress of high strength bolts for bridges

The axial stress of high strength bolts for bridges affects the service life directly, it is necessary to measure it regularly. Based on the theory of acoustic elasticity and combination of longitudinal and shear waves, a new theoretical analysis method is proposed. The stressed and non-stressed areas of bolt are separated, and the derived formula only use the flight time and difference of acoustoelastic coefficients to get axial stress. Further, the preload experiments with high strength bolts of grade 8.8S and 10.9S is designed, the experimental results show that the proposed method is applicable to the axial stress of the bridge bolts with any specifications, material and different screwing depth used in this paper, the effect of elastic deformation on the flight time is eliminated, and the measuring error is within 5%.

Tubing String Thread Sealing Surfaces Damage Evaluation Based on Acoustic Elasticity Theory

During the processing of tubing premium threaded made up, the degree of the thread sealing surface intactness will directly affect the sealing performance of the string. Nevertheless, there are some difficulties to detect the damage of the engaged sealing surface effectively. In the present study the sealing surface damage was judged by the sealing surface contact stress’s relative changes according to the acoustic elasticity theory,. At the same time, the wear defects generated at the tubing sealing surface, during the tubing made up, contrasted with the wear and unworn surface roughness of coupling ultrasonic detected about the sealing surface. The results showed that with the acoustic amplitude evaluated the sealing contact stress was susceptible to the influence of surface roughness of coupling. But the reflection wave with the center frequency on the sealing surface characterization of the contact stress could avoid this problem effectively.

Investigations of the Structural and Strain-Stress State of the Rails of Current Production by the Acoustic Elasticity Method

Представлены результаты экспериментальных измерений остаточных напряжений в элементах рельса, измеренных электромагнитно-акустическим структуроскопом СЭМА с использованием метода акустоупругости. Оценка внутренних напряжений произведена также в отдельных элементах рельса. Настройка чувствительности структуроскопа СЭМА и определение коэффициента акустоупругой связи выполнены в лабораторных условиях путем создания в отрезке рельса напряженного состояния одноосного сжатия в направлении продольной оси на испытательной машине Instron 300DX. Отмечена высокая чувствительность и достоверность измерений с погрешностью определения механических напряжений до 2 МПа и соответствие зарегистрированных структуроскопом механических напряжений нагрузке рельса, реализуемой на стенде. Остаточные напряжения, определяемые акустоупругим методом по измеряемой разнице времени пробега двух ортогонально поляризованных сдвиговых волн на участке от головки до подошвы и обратно, являются усредненными по сечению рельса и несут информацию о величине продольных напряжений в рельсе. Диапазон разброса измеренных в лаборатории остаточных напряжений в отрезках рельсов составил 49…67 МПа. С ростом сжимающей нагрузки происходит уменьшение скорости головной волны на всех измеряемых участках рельса. Для относительной оценки остаточных напряжений в отдельных элементах рельса выполнены измерения скорости распространения акустических волн по головке, шейке и подошве, показавшие, что остаточные напряжения в продольном направлении рельса, как правило, носят сжимающий характер для головки и растягивающий - для шейки.

One Micro-thrust Measurement Method Based on the Acoustoelastic Theory

Concerning the traditional way of micro-thrust measurement cannot get the transient thrust value with high precision and the measuring process of piezoelectric sensors is sensitive to the electromagnetic interference, this paper builds one new measurement method basing on the acoustic elasticity theory. The acoustoelastic element is the core of the whole system as it can transform the thrust changes into the variation of acoustic time. Thus adopting a timer to record such variation so that the thrust changes in real-time could be obtained, which is helpful for studying the mechanism of micro thrusters. This method built in this paper is not only non-contact and non-destructive but also easy to operate with simple structure and high precision.

Measurement of Welding Residual Stress by Ultrasonic Technology

An ultrasonic method was developed to measure the residual stress in a welded joint based on the modified acoustic-elasticity theory. Phase frequency analysis method was introduced by incombination with shear wave and longitudinal wave. The acoustic-elasticity parameters of joint material was derived by ultrasonic inspection during loading experiment. Transverse and longitudinal residual stress was determined by precisely measuring of short-distance acoustic travel time. The ultrasonic measurement results was confirmed by H&K theory and XRD methods with good repeatability and reliability.

Non-Destructive Measurement of Residual Stresses by an Ultrasonic Method

An ultrasonic computerized complex for measurement of residual and applied stresses UltraMARS® was recently introduced. Average through thickness stresses can be measured based on the acoustic-elasticity effect, according to which the velocity of elastic wave propagation in solids is dependent on the mechanical stress. The system was used successfully in numerous applications proving to be a reliable, fast and economical way to evaluate residual and applied stresses in materials and structures. The newly developed complex was used in a number of applications that called for non-destructive evaluation of stresses. Examples of such applications will be discussed in the paper. The system was further developed to allow for measurement of subsurface and surface stresses in structural materials and made of them structures.