Stress Wave Method Research Articles

Theoretical elucidation on the empirical formulae for the ultrasonic testing method for concrete structures

The main purpose of this paper was to theoretically elucidate the compressive strength of concrete using the empirical formula with exponential form for the ultrasonic testing method through a generalization of the one-dimensional wave equation. The approximate solutions derived from a generalization of the one-dimensional wave propagation theory using the separation of variables method can be represented as the exponential form. If the viscosity of the concrete materials in stress wave method is neglected, the elastic waves can then be reduced to the ultrasonic waves. Through the membership function concept in the fuzzy set theory, the approximate solution with exponential form can be represented as the empirical formulae for the ultrasonic testing method in predicting the compressive strength of concrete. This present study indicates that both the ultrasonic pulse velocity (UPV) and ultrasonic pulse amplitude (UPA) methods are just a special case of the combined method. The predicted results of the combined method are actually better than the results obtained from either the UPV or UPA method.

Breeding radiata pine for wood stiffness: review and analysis

Summary Radiata pine is widely planted in the southern hemisphere, and has a versatile timber. The mature wood of this species is strong and stiff enough for a number of industrial uses, but current trends of harvesting at below 30 years result in a high proportion of low-stiffness juvenile wood. Radiata pine breeders have countered this reduction, indirectly, by selecting progenies for dense juvenile wood. However there is evidence now that improving juvenile wood density may not be sufficient to fully address low stiffness. This has led to work on assessing stiffness itself, and to studies on using microfibril angle in the tree improvement program. Progress on breeding radiata pine for stiffness in New Zealand is reviewed in this paper, with a briefer account of work in Australia. Several direct and indirect methods to improve stiffness arc described. These include static bending tests on boards and small clear specimens, acoustic and stress wave methods, and microfibril angle, in addition to density and pilodyn penetration. Two tools using acoustic/stress wave methods have been developed by the New Zealand forestry industry, and are being used operationally to segregate logs. A third tool (FAKOPP), developed in Hungary, shows promise for use on standing trees and hence could be suitable in screening progenies. SilviScan is an important Australian breakthrough and could potentially be used to predict longitudinal stiffness on hundreds of short samples per day. Combining acoustic/stress wave results with density and branch cluster frequency could well be a viable and cost—effective way to select progenies for clearwood stiffness in the juvenile wood zone. Information on stiffness could be combined with breeding values for growth rate, straightness and grain spirality to select parents for deployment and breeding.

Assessment of Pile Integrity by Low-Strain Stress Wave Method

This paper discusses the application and limitations of the stress wave method for the assessment of pile Integrity. Equations for the calculation of wave reflection and transmission are derived as related to the interpretation of test results. An idealized pile with a necking linkend section is analyzed using the theoretical equations to show typical wave reflections from the necking section and from the pile toe. The instrument used for pile integrity testing is briefly described. Original data from a field verification exercise of pile integrity testing in Beijing, China are presented and interpreted. Original data from a test performed on a precast prestressed concrete pile connected in four segments in Hang Kong are also presented and interpreted. The data measured from the field show that the measured velocity wave is, in general, more complicated than that described by the idealized stress wave equation. Factors affecting test results and limitations of the testing method are discussed and summariz...

42397 Stress wave method for measuring elastic moduli of powder compacts in tension and compression : Al-Hassani, S.T.S.; Tennant, P.W.; Sarumi, M.A. Powder Metallurgy, vol. 32, no. 3, pp. 204–208 (1989)

42397 Stress wave method for measuring elastic moduli of powder compacts in tension and compression : Al-Hassani, S.T.S.; Tennant, P.W.; Sarumi, M.A. Powder Metallurgy, vol. 32, no. 3, pp. 204–208 (1989)

Pile integrity test by stress wave method : Horiguchi, T; Murakami, H; Shigematsu, H; Tsuzuki, M Drivability of Piles, Proc Discussion Session 14, 12th International Conference on Soil Mechanics and Foundation Engineering, Rio de Janeiro, 13–18 August 1989V1, P59–62. Publ Tokyo: JSSMFE, 1989

Pile integrity test by stress wave method : Horiguchi, T; Murakami, H; Shigematsu, H; Tsuzuki, M Drivability of Piles, Proc Discussion Session 14, 12th International Conference on Soil Mechanics and Foundation Engineering, Rio de Janeiro, 13–18 August 1989V1, P59–62. Publ Tokyo: JSSMFE, 1989

Stress Wave Method for Measuring Elastic Moduli of Powder Compacts in Tension and Compression

A test is described in which a cylindrical powder pellet is sandwiched between two steel rods (input and output bar), aligned linearly. The free end of the input bar is struck by a small projectile, propagating a low intensity, short duration, compressive stress pulse across the specimen to the free end of the output bar. This pulse is then reflected, causing the pellet to be loaded in tension. The strain pulses in the two bars are used to determine the elastic Young's modulus in tension and compression and the tensile strength of the pellet. Details are given of the apparatus used and the theory for calculation of the specimen stress and strain. The results are found to compare well with both uniaxial tension and diametral ‘Brazilian’ tests. The method is believed to be applicable to a wide range of powder compacts and porous materials. PM/0503

Strength of Old Wood Joists

Two nondestructive techniques are used to evaluate the strength of wood joists in an existing structure. The traditional visual grading and longitudinal stress wave approaches are employed, with the latter technique providing better insight into the strength of the floor system. Further refinements of the stress wave method are suggested.

Techniques for studying strain rate effects in brittle materials

AbstractTechniques for studying brittle fracture over a strain rate range of 10−7–101 in./in./sec. and at temperatures from 75 to 1800°F are discussed. Techniques for achieving a uniaxial tensile stress in prismatic bars via a reflected stress wave method at strain rates up to 103 in./in./sec. at room and elevated temperatures are presented. Results of the aforementioned effects in flexure, and experimental verification of the stress‐time‐position history for the stress wave loading technique are presented along with applicable theoretical explanations. Applications of the above techniques to a broader spectrum of brittle and semi‐brittle materials are described.