Bolt Strain Research Articles

Monotonic Loading Tests on Semi-Rigid End-Plate Connections with Welded I-Shaped Columns and Beams

8 specimens of beam-to-column bolted end-plate connections with various details and welded I-shaped section columns and beams were tested under monotonic loads. Based on the specification for the end-plate connection rotation proposed, the contribution of the panel zone and the gap between the end-plate and column flange to the joint rotation have been obtained. The influences of both flush and extended types, column stiffeners, end-plate rib stiffeners, bolt sizes and end-plate thicknesses etc on the joint behaviour have been compared. The test results indicate that all these connections tested are typically semi-rigid. For the flush and extended end-plate connection, the joint rotation mainly derives from the relative deformation between the end plate and the column flange and the shearing deformation of the panel zone respectively. Using a special method to measure bolt strain, the bolt tension forces and their development and distribution have been depicted and studied, and two bolt tension force distribution models for end-plate connections using pretensioned bolts are recommended.

健全性診断機能を付与した機械的継手部の革新設計

The primary objective of this study is to address a key research challenge for improving tradi-tional joint design, which develop functions and structures that can monitor their own structural integrity. A self-sensing technique using the bolt itself to monitor the bearing damage in bolted composite or metallic joints is proposed. The basic concept is based on making Bolt Gauge (BG) measurements. That is, have only to bond a strain gauge onto the surface of bolt head to reflect changes in the bolt strain, which would identify the state of bearing damage. Novel system can maintain not only the peculiar structures and functions of the mechanical fastener, but more importantly, also can provide the self-diagnostic function for component damage. And, it can be contributed directly to technology development for structural health monitoring (SHM) to address these issues, and to meet demanding goals in increasing aerospace vehicle safety and reliability while reducing operating costs. Extensive tests using double lap bolted joint specimen are performed to verify this technique in the various joint cases. The investigations include the effects of the bolt clamp-up, material response, joint geometry and loading history on the detection sensitivities for the bearing damage. The onset and progress of the bearing damage monitored by BG measurements are also compared with acoustic emission (AE) measurements that used in traditional NDE method. A further consideration of the detection mechanisms by BG including an axial loading test and a three-dimensional finite element analysis is performed. The behavior of bolt deformation and stiffness degradation due to the bearing damage initiation and progression are estimated using damage mechanics approach.

Influence of Aster Yellows Phytoplasma on the Fitness of Aster Leafhopper (Homoptera: Cicadellidae)

This study revealed that feral aster leafhoppers, Macrosteles quadrilineatus Forbes, exposed to aster yellows phytoplasma live longer and may lay more eggs than nonexposed leafhoppers. Aster leafhoppers were reared on asters infected with either of 2 strains of aster yellows phytoplasma or uninfected asters. After eclosion, adults were placed on uninfected healthy lettuce or oat plants and transferred periodically. The life span of test leafhoppers and the number of offspring they produced were compared. Females reared on noninfected aster plants lived for an average of 19 d, those reared on ‘severe’ and ‘bolt’ strain aster yellows phytoplasma-infected plants lived 26 and 28 d, respectively. The mean number of offspring produced by females reared on the bolt strain of aster yellows phytoplasma-infected asters was almost twice the number produced by nonexposed leafhoppers. The life span of feral leafhoppers or the number of eggs laid did not differ for leafhoppers maintained on either oats or lettuce after exposure to aster yellows phytoplasma-infected asters. Female leafhoppers lived twice as long as males. Our results suggest that the aster leafhopper may have had a long association with aster yellows phytoplasma. The longer life and higher fecundity of phytoplasma-infected leafhoppers may influence disease dynamics of aster yellows in lettuce.

The embrittlement characteristics of large turbine casing bolts: the influence of service induced strain

The present article attempts to describe an assessment of the effects of accumulated permanent service strain on the degree of toughness losses, caused by reverse temper embrittlement (RTE) experienced by large turbine casing bolts during high temperature service. Effectively, it was established that (a) reported studies in this area were scarce, (b) the early work exhibited somewhat contradictory trends while (c) the post 1990 studies indicated that the presence of strain exacerbated the extent of RTE. The few modern day studies suggested that the effects of strain in low alloy steel bolts were greatest at low levels of up to around % ϵ∽0.5% and the trend could be described by the expression: C N= A(% ε) −0.8, where C N was the normalised ambient Charpy energy and A was a scaling coefficient. Also the Charpy fracture appearance transition temperature (FATT) was also shown to increase in proportion to (% ϵ) −0.8. One study has reported an embrittlement constant, termed C RTE, which was a function of grain size and bulk %P in the steel, and whose value determined the likelihood of bolt embrittlement during service, i.e., low values predicted embrittlement with high values indicating non-embrittlement during service. It was reported that strain decreased the value of C RTE. Within the strain range 0.2% to 0.6% one study established that the effects could be described as follows: C RTE =0.35−0.44×(% ε), while at lower strain values another study reported that C RTE=0.0772×(% ε)−0.64. Note that the exponent in the latter expression was similar to that which described the normalised Charpy energy trends. It has been suggested that the total RTE effects, or toughness losses, were the summation of two separate processes, viz., a temperature-time controlled grain boundary phosphorus segregation component and a strain induced grain boundary phosphorus segregation component. The latter was thought to be related to enhanced phosphorus movement along certain dislocation networks, caused by plasticity, to grain boundary locations. Although the data was scarce, it was suggested that the degree of grain boundary segregation by phosphorus during high temperature service increased with increasing levels of strain. This trend between the atomic fraction of grain boundary phosphorus C GB P and accumulated strain was simply described numerically as C GB P=10.54×(% ε) 0.35. Finally, actual bolt strain distributions with service times in real working situations are discussed together with considering both embrittlement and creep damage degradation acting together with time, or accumulated service strain.

Laboratory evaluation of a new cable bolt tension meauring device

Abstract The development and testing a of new instrument called Cable Tension Measuring Device (CTMD) are presented. The CTMD consists of a vibrating wire strain gauge which is mounted on two holding anchors fixed on the cable. The device accommodates the twisting effect of the cable bolt and is easy to install. Calibration and short-term laboratory tests are reported herein. Comparison of cable bolt strain distributions obtained during pullout tests from CTMD and Tensmeg gauges show very good agreement.

Effects of Temperature and Vector Age on Transmission of Two Ohio Strains of Aster Yellows Phytoplasma by the Aster Leafhopper (Homoptera: Cicadellidae)

Mean latent period and transmission rate of 2 strains bolt and severe ) of aster yellows photo plasma in nymph and adult aster leafhopper’s, Macrosteles quadrilineatus Forbes, were studied under controlled conditions at 15, 20, 25, and 30. There was a nonlinear relationship between mean latent period and temperature with shorter mean latent periods at higher temperatures (≈20-25 d) than at lower temperatures (≈40-80 d) for both aster yellows phytoplasma strains and both ages of leafhoppers. The proportion of leafhoppers that became vectors was significantly higher for bolt strain when leafhoppers acquired aster yellows phytoplasma as nymphs than as adults. However, there was no difference in the proportion that became vectors of the severe strain by the 2 age groups. Once leafhoppers became inoculative, the rate of transmission remained constant over their life spans when monitored by serial transfers at 48-h intervals. Increases in temperature and access time of leafhoppers increased tile proportion of leafhoppers that became vectors after feeding on bolt strain-infected plants. Also, the effect of aster yellows phytoplasma exposure on life spans of leafhoppers was studied at 4 temperatures. At 25 and 30, leafhoppers exposed to both aster yellows phytoplasma strains lived longer than those leafhoppers not exposed. Data can be used in an aster yellows epidemiological model to evaluate strategies for aster yellows management.

Automatic roof bolt strain monitoring in coal mines : E. Layer, International Journal of Rock Mechanics & Mining Sciences, 33(1), 1996, pp 93–95

Automatic roof bolt strain monitoring in coal mines : E. Layer, International Journal of Rock Mechanics & Mining Sciences, 33(1), 1996, pp 93–95

Automatic roof bolt strain monitoring in coal mines

Automatic roof bolt strain monitoring in coal mines

An Introduction to the Design and Behavior of Bolted Joints

Abstract Although the title of this book includes the word “introduction”, the treatment of the subject is extensive and complete. The material goes well beyond the coverage of bolted joint design received in a typical undergraduate machine design course. The easy-to-read text begins with the fundamentals of bolt strength, deformation, and material selection and proceeds to cover the topics of preload, torque, and stretch control. The emphasis is on practical considerations for the efficient design of joints, including cost, ease of assembly, inspection, and disassembly. This second, revised edition has expanded the coverage of corrosion, fatigue, gaskets, and ultrasonic measurement of bolt strain. Also included are discussions of the failure modes and mechanisms of bolted joints. Case histories from industry are presented throughout the text to illustrate key points. Many up-to-date references are presented at the end of each chapter to allow the reader to pursue individual topics further, if desired. The text contains several appendices with useful tables and formulas for quick reference. The author has broad experience in the subject area from many years as a consultant to the power generation and nuclear industry, active participation on society working groups such as ASME and PVRC, as well as the presentation of numerous seminars on the topic. This book would serve as a valuable desk reference for engineers concerned with the design and performance of bolted joints.

Effect of oxidation on integrity of bolted structures

Oxide growing on mild and low alloy steel components in the high pressure CO2 based coolant of UK gas cooled nuclear power stations can become porous and continue to grow at the interfaces of structural components even when any interfacial gap has filled with oxide. Because such growth gives rise to a net volume expansion, the adjacent components can be forced apart. Any fastening, such as a weld or bolt, holding them together can then become stressed as a result of growth of oxide alone, and may sustain mechanical damage. The phenomenon is now well understood and methods of predicting behaviour have been developed and refined over the years to ensure safe and continued plant operation. The basis of such methods is presented for bolted joints, and the way in which joint geometry, environment, and mechanical properties of component material can affect bolt strain is outlined with examples.MST/1125

Effect of oxidation on integrity of bolted structures

Abstract Oxide growing on mild and low alloy steel components in the high pressure CO2 based coolant of UK gas cooled nuclear power stations can become porous and continue to grow at the interfaces of structural components even when any interfacial gap has filled with oxide. Because such growth gives rise to a net volume expansion, the adjacent components can be forced apart. Any fastening, such as a weld or bolt, holding them together can then become stressed as a result of growth of oxide alone, and may sustain mechanical damage. The phenomenon is now well understood and methods of predicting behaviour have been developed and refined over the years to ensure safe and continued plant operation. The basis of such methods is presented for bolted joints, and the way in which joint geometry, environment, and mechanical properties of component material can affect bolt strain is outlined with examples.MST/1125

Bolting and loss of contact between cylindrical flat-flanged joints without gaskets

Four bolts of a lightweight, steel, flanged joint were strain-gauged to measure bolt tension and bending. Three-dimensional, finite element analysis was used to determine bolt strains and gaps between the flanges due to axial tension and internal pressure for three different contact conditions. Two joints were tested. The front faces of the first joint were nominally flat while the second had a small negative cone angle (⋍ 0 degrees 15 minutes) so that flanges initially touched at the outside only. The non-linearity of experimental bolt strain with external load shows that the contact area around the bolts decreases with increasing axial tension. Comparison with the finite element predictions shows the rate at which the contact area diminishes. The finite element results also demonstrate that flange deflection is underestimated when contact area loss is ignored, and the consequences for leakage prediction are explained.

A CW ultrasonic bolt-strain monitor

There exists a need for a relatively inexpensive system for measuring strain in bolts. The torque wrench is one technique for straining bolts which has been widely applied. Unfortunately, friction in the bolt threads and between the nut and the work tend to make such a simple system inaccurate. In practice, a torque wrench is unacceptable for many situations where strain is critical. In this article, an ultrasonic technique is described which can indicate changes in bolt strain to better than one part in 104. The technique is based on the one-dimensional propagating-ultrasonic-wave model and uses a new ultrasonic instrument called a Reflection Oscillator Ultrasonic Spectrometer which is a closed-loop feedback marginal-oscillator system that frequency locks the device to the peak of a mechanical resonance in the bolt. The instrument indicates a shift in the bolt resonance frequency due to elongation and changes in velocity of sound due to strain. Data are presented comparing a standard torque wrench to the ultrasonic monitor for different measured stresses on the bolt as well as for different bolt conditions. The strain instrument can be used to monitor changing stresses, to measure material properties and may be applied as a strain gage or load cell.