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RESEARCH PAPERS: Reliability, Stress Analysis, and Failure Prevention

J. Vib., Acoust., Stress, and Reliab. 1986;108(3):241-248. doi:10.1115/1.3269334.

This paper describes an approach to life prediction in which critical elements of major structural components are continuously monitored by appropriate damage indicators for structural damage, and, based on the indicated damage state, an on-line assessment is made of the remaining life. Concurrently alternative corrective measures can then be assessed and, if the life has been found wanting, appropriate actions taken. The process is viewed as a continuous one whereby the current remaining life of critical elements is known as the plant ages. The need for applying such procedures becomes increasingly important as some of our major structures approach their design life and concerns arise regarding retirement and replacement versus life extension. Important elements of this approach include definitions of damage, appropriate damage monitors, damage assessment, life prediction, and conseqeunces of corrective action. This paper treats these elements in the context of past history and current programs associated with pipe cracking in nuclear power plants.

Commentary by Dr. Valentin Fuster
J. Vib., Acoust., Stress, and Reliab. 1986;108(3):249-254. doi:10.1115/1.3269335.

The power spectrum of the stress induced by a narrow-band (vortex shedding) and broad-band (impingement, near field) flow noise on a simply supported square plate is used to determine the fatigue failure probability of that plate. A lognormal distribution of the material properties and a Rayleigh distribution of the stress peaks are implied in the statistical model. The Poisson failure rate and reliability are computed for several crack propagation factors and statistical distributions of the initial strength of materials. The plate fatigue lifetime obtained by statistical analysis is generally shorter than the one given by a deterministic Palmgren-Miner cumulative model for narrowband and broad-band excitations. The two models predict similar fatigue lifetime for cases corresponding to small initial material cracks or low rates of crack propagation.

Commentary by Dr. Valentin Fuster
J. Vib., Acoust., Stress, and Reliab. 1986;108(3):255-261. doi:10.1115/1.3269336.

Precision multiple roller power transmissions are investigated in this work. These chains transfer significant power and move with very high velocity. They are subjected to variable loading with strong vibration and impact components, and require forced stream lubrication. Because of these severe working conditions, chain life is limited by the fatigue, and the chain plates are the weakest elements in many cases. It is shown that fatigue life is significantly decreased by fretting action, high stress concentration in the plates, and the impossibility of maintaining a uniform force distribution across the multiple lines of a chain. The results of the performed experimental stress analysis under static and variable loading are given for the different plate geometries. The plates with a variety of stress reducers located in different areas are investigated, and theoretical and effective stress concentration factors are determined. Based on that, new plate chain designs are proposed. These new designs use fewer lines to transfer the same power as conventional chains.

Commentary by Dr. Valentin Fuster
J. Vib., Acoust., Stress, and Reliab. 1986;108(3):262-267. doi:10.1115/1.3269337.

The interactive effects of high- and low-cycle loading on crack growth were evaluated for a high-temperature engine disk alloy (Inconel 718) over a wide range of low-cycle hold times, low-cycle stress intensity factor range (ΔK), high-cycle ΔK , and high-cycle frequency up to 1825 Hz. A series of fatigue crack growth experiments were carried out with a constant low-cycle ΔK and an increasing high-cycle ΔK. The high-frequency ΔK and crack length were measured with sufficient precision to capture details of the transition from the low-cycle dominated regime to the high-cycle dominated regime. In these experiments, the low- and high-cycle dominated growth regimes remained distinct over the entire range of low cycle ΔK, low cycle hold time and frequency investigated. An interactive effect apparent in the low-cycle dominated regime, was a retardation of the low-cycle growth rate when high-cycle loading was applied. The degree of retardation varied with low-cycle ΔK and frequency.

Commentary by Dr. Valentin Fuster
J. Vib., Acoust., Stress, and Reliab. 1986;108(3):268-275. doi:10.1115/1.3269338.

This paper reviews the experimental work on the influence of variable amplitude or random loads on the mechanics and micromechanisms of fatigue crack growth. Implications are discussed in terms of the crack driving force, local plasticity, crack closure, crack blunting, and microstructure. Due to heterogeneity in the material’s microstructure, the crack growth rate varies with crack tip position. Using the weakest link theory, an expression for crack growth rate is obtained as the expectation of a random variable. This expression is used to predict the crack growth rates for aluminum alloys, a titanium alloy, and a nickel steel in the midrange region. It is observed using the present theory that the crack growth rate obeys the power law for small ΔK and that the power is a function of a material constant.

Commentary by Dr. Valentin Fuster
J. Vib., Acoust., Stress, and Reliab. 1986;108(3):276-281. doi:10.1115/1.3269339.

The cyclic fatigue behavior of a resinoid-bonded abrasive was determined in ambient air (22°C and 50 percent relative humidity). The number of cycles to failure was dependent on the cyclic stress by a power functional relation, consistent with fracture mechanics concepts of fatigue crack growth. Additionally, it was found that the cyclic fatigue behavior did not depend on the cyclic stress waveform or the test sample geometry and loading (four-point bend bars and radically loaded nonreinforced and reinforced wheels). Based upon fracture mechanics concepts, a reliability analysis was developed for reinforced, resinoid-bonded abrasives in service, taking into account the variability in strength and the fatigue behavior exhibited by these materials.

Commentary by Dr. Valentin Fuster
J. Vib., Acoust., Stress, and Reliab. 1986;108(3):282-287. doi:10.1115/1.3269340.

A finite element technique using the eight-node quadrilateral isoparametric element is presented to calculate stress intensity factors in orthotropic plates. The procedure is general so as to include multilayered laminates with varying laminae directions and thicknesses. This method can easily solve problems with various loading conditions and plate geometry. Several examples with solutions available in literature are solved to examine the accuracy of the current approach. Solutions of more complicated and practical engineering fracture problems are also presented to demonstrate the versatility of this method.

Commentary by Dr. Valentin Fuster
J. Vib., Acoust., Stress, and Reliab. 1986;108(3):288-295. doi:10.1115/1.3269341.

A simple method of analysis using force polygon diagrams is proposed for determining roll torque and pressing load, in particular plane-strain ring rolling processes. Pressing velocity together with driven roll rotation is incorporated in constructing the hodograph for the upper-bound analysis in order to find an optimized tangential velocity pattern. Results from two types of tangential velocity discontinuity patterns and related force polygon diagrams are compared at optimized values. The ratio of resultant friction force and pressing load, or an equivalent coefficient of friction is determined from the force polygon diagrams. Experiments were carried out with AISI 1045 steel blanks in a hot condition. Theoretical torques and pressing loads are in good agreement with the experimental values. It is shown that the present method can be efficiently used for predicting pressing load and roll torque in ring rolling; the method has a flexibility and simplicity which recommends it for engineering analytical purposes and for explaining related physical phenomena.

Commentary by Dr. Valentin Fuster

RESEARCH PAPERS: Noise Control and Acoustics

J. Vib., Acoust., Stress, and Reliab. 1986;108(3):296-300. doi:10.1115/1.3269342.

A variety of methods for the prediction of acoustic resonances in heat exchangers are recommended in the literature. There is currently no clear guideline available to designers for the avoidance of these resonances. This paper compares some of the latest developments in this field, proposes a new procedure for design and outlines a specific example of the procedure.

Commentary by Dr. Valentin Fuster
J. Vib., Acoust., Stress, and Reliab. 1986;108(3):301-307. doi:10.1115/1.3269343.

Measurements were made of the wall pressure field beneath separated/reattached boundary layer flows. These flows consisted of two types; flow over a forward-facing step and flow over a backward-facing step. Wall pressure fluctuations from an equilibrium flat plate boundary layer flow were also measured and used as a baseline for comparative purposes. Values of the RMS fluctuating pressure as well as the frequency spectral density, phase velocity, and coherence of the surface pressure field were measured at various locations upstream and downstream of the steps. The experimental results show that the separation-reattachment process produces large-amplitude, low-frequency pressure fluctuations. The measured spectral statistics of the wall pressure fluctuations are consistent with the view that at reattachment there exists a region of coherent highly energized velocity fluctuations located near the wall which, as it convects downstream, decays and diffuses away from the wall. This energized region remains identifiable in the wall pressure statistics as far as 72 step heights downstream of the backward-facing step.

Commentary by Dr. Valentin Fuster
J. Vib., Acoust., Stress, and Reliab. 1986;108(3):308-314. doi:10.1115/1.3269344.

The flow and wall-pressure field around a wing-body junction has been experimentally investigated in a quiet, low-turbulence wind tunnel. Measurements were made along the centerline in front of the wing and along several spanwise locations. The flow field data indicated that the strong adverse pressure gradient on the upstream centerline causes three-dimensional flow separation at approximately one wing thickness upstream and this induced the formation of the horseshoe root vortex which wrapped around the wing and became deeply embedded within the boundary layer. The wall-pressure fluctuations were measured for their spectral content and the data indicate that the effect of the adverse pressure gradient is to increase the low-frequency content of the wall pressure and to decrease the high-frequency content. The wall pressure data in the separated region, which is dominated by the horseshoe vortex, shows a significant increase in the low-frequency content and this characteristic feature prevails around the corner of the wing. The outer edge of the horseshoe vortex is clearly identified by the locus of maximum values of RMS wall pressure.

Commentary by Dr. Valentin Fuster
J. Vib., Acoust., Stress, and Reliab. 1986;108(3):315-321. doi:10.1115/1.3269345.

The equations of momentum and continuity are combined and linearized yielding the one-dimensional nonhomogeneous acoustic wave equation. Three terms in the nonhomogeneous equation act as acoustic sources and are taken to be forcing functions acting on the homogeneous wave equation. The three source terms are: fluctuating entropy, turbulence gradients, and turbulence-flame interactions. Each source term is discussed. The turbulence-flame interaction source is used as the basis for computing the source acoustic pressure from the Fourier transformed wave equation. Pressure fluctuations created in turbopump gas generators and turbines may act as a forcing function for turbine and propellant tube vibrations in earth-to-orbit space propulsion systems and could reduce their life expectancy. A preliminary assessment of the acoustic pressure fluctuations in such system is presented.

Commentary by Dr. Valentin Fuster
J. Vib., Acoust., Stress, and Reliab. 1986;108(3):322-328. doi:10.1115/1.3269346.

The concept and potential use of acoustic agglomeration as an aerosol conditioning device in a clean-up team is discussed. The experimental setup used for carrying out the room temperature agglomeration tests is briefly described. Photographic evidence is presented showing the survival of bonds holding the acoustically agglomerated particles together, after the particles were size separated in an (Anderson Mark II) inertial impactor. A theoretical analysis is developed which shows that the shearing stresses exerted on particles in the impactor are higher than would be experienced if they were being separated in a typical industrial cyclone. Thus, it is concluded that the acoustically agglomerated particles are “robust” enough to avoid breakup in a cyclone (a common industrial particle removal device).

Commentary by Dr. Valentin Fuster
J. Vib., Acoust., Stress, and Reliab. 1986;108(3):329-338. doi:10.1115/1.3269347.

Noise generated by control valves in power generation, chemical and petrochemical plants must be predictable so that proper design measures can be taken to conform to OSHA’s noise regulation. Currently available noise prediction methods are empirically based and not sufficiently accurate. The method proposed is based on jet noise theory for both subcritical and choked conditions, duct acoustics theory in terms of higher order mode generation and propagation, and the theory of acoustics-structure interaction in the development of the transmission loss values for the pipe. One third octave values are calculated over the audio spectrum by incorporating spectral aspects of noise generation, propagation, transmission, and radiation. The predicted values of noise for several size cage globe valves over wide pressure ranges compare well with measured results by two prominent valve manufacturers. The method, at present, is restricted to conventional valve styles, as opposed to the special low noise valve types with their very complicated orificial elements.

Commentary by Dr. Valentin Fuster

RESEARCH PAPERS: Vibration and Sound

J. Vib., Acoust., Stress, and Reliab. 1986;108(3):339-347. doi:10.1115/1.3269348.

The hydrodynamic mass approach to the solution of dynamic problems in coupled fluid-cylindrical shells is reviewed; simplified equations for computing the hydrodynamic masses and for the subsequent solution of the eigenvalue problem are given in several commonly encountered special cases. Methods of incorporating the hydrodynamic mass concept into finite element structural analysis computer programs for the more general cases are discussed.

Commentary by Dr. Valentin Fuster
J. Vib., Acoust., Stress, and Reliab. 1986;108(3):348-353. doi:10.1115/1.3269349.

An interative method has been developed for analyzing dynamic loads in a light weight basic planetary gear system. The effects of fixed, semi-floating, and fully-floating sun gear conditions have been emphasized. The load dependent variable gear mesh stiffnesses were incorporated into a practical torsional dynamic model of a planetary gear system. The dynamic model consists of input and output units, shafts, and a planetary train. In this model, the sun gear has three degrees of freedom; two transverse and one rotational. The planets, ring gear, and the input and output units have one degree of freedom, (rotation) thus giving a total of nine degrees of freedoms for the basic system. The ring gear has a continuous radial support. The results indicate that the fixed sun gear arrangement with accurate or errorless gearing offers in general better performance than the floating sun gear system.

Commentary by Dr. Valentin Fuster
J. Vib., Acoust., Stress, and Reliab. 1986;108(3):354-361. doi:10.1115/1.3269350.

Stepping motors have several advantages over other motor systems, especially in the field of digital control system; however, they also have a disadvantage in that the vibrational exciting source exists within their driving principle. This study deals with this vibrational problem of stepping motored machine system in consideration of the interaction between mechanical and electrical parts of the system. In this report one basic mathematical modeling, i.e., Spanworm equation, is proposed for analysis and applied to some practical examples. The calculational results agree well with measured results. Consequently, to install the stepping motors in a machine system, the usefulness of Spanworm equation is endorsed.

Commentary by Dr. Valentin Fuster
J. Vib., Acoust., Stress, and Reliab. 1986;108(3):362-368. doi:10.1115/1.3269351.

Statistical analysis of the gear dynamic load is carried out using piecewise constant mesh stiffness approximation. The dynamics of the spur gear system is modeled as a nonlinear, nonstationary process, and the gear transmission error which acts as a random input to the gear system is generated by passing a Gaussian white noise process through a time invariant shaping filter. The equivalent discrete time state equation and the mean and covariance propagation equations are then written for the augmented system. Then starting from known initial conditions these propagation equations are used to compute the statistics of the steady state response and hence those of the dynamic load. A procedure is presented for the selection of proper initial conditions so as to reach the steady state condition faster, thereby reducing the computational time required. The variations in the statistics of the dynamic load with respect to changes in contact position, random error magnitude, and operating speed are also investigated with the help of a numerical example. The results show that the approach presented in this study provides truer results than the statistical linearization approach used by Tobe et al. [13]. Moreover, the proposed procedure has the advantage that it can be applied to higher-order systems with complex mesh stiffness and torque fluctuations and to systems with symmetrical or nonsymmetrical nonlinearities.

Commentary by Dr. Valentin Fuster

RESEARCH PAPERS: Fastening and Joining

J. Vib., Acoust., Stress, and Reliab. 1986;108(3):369-376. doi:10.1115/1.3269352.

A new method is presented for the analysis of a bolted flange subjected to bending moments. Bolt axial cyclic loads are calculated using the force ratio method. Bolt bending moments are found with the new analysis scheme presented. A key factor in the analysis is the area in compression of the flange. Experimental results are used to substantiate the theoretical methods. A finite element analysis was also conducted to support the theory.

Commentary by Dr. Valentin Fuster

TECHNICAL BRIEFS

J. Vib., Acoust., Stress, and Reliab. 1986;108(3):377-378. doi:10.1115/1.3269353.

The transmission of gear tooth meshing vibration from the tooth contact region to the shaft, through rolling element bearings and then through the gearbox casing can have an important influence on the measured vibration sepctrum. In critical applications the measurement of the torsional vibration of the gear may be preferable.

Commentary by Dr. Valentin Fuster
J. Vib., Acoust., Stress, and Reliab. 1986;108(3):378-381. doi:10.1115/1.3269354.

An optimization procedure in the design of a viscoelastic dynamic damper is proposed for a single-degree-of-freedom primary system with the effects of prestrain taken into account. The performance is compared with that by a conventional spring-dashpot-mass damper. Applicability of the proposed procedure to a resonance-frequency-varying system is also shown.

Commentary by Dr. Valentin Fuster

BOOK REVIEWS

J. Vib., Acoust., Stress, and Reliab. 1986;108(3):382-383. doi:10.1115/1.3269355.
FREE TO VIEW
Abstract
Commentary by Dr. Valentin Fuster
J. Vib., Acoust., Stress, and Reliab. 1986;108(3):383-384. doi:10.1115/1.3269356.
FREE TO VIEW
Abstract
Commentary by Dr. Valentin Fuster
J. Vib., Acoust., Stress, and Reliab. 1986;108(3):384-385. doi:10.1115/1.3269357.
FREE TO VIEW
Commentary by Dr. Valentin Fuster
J. Vib., Acoust., Stress, and Reliab. 1986;108(3):385-386. doi:10.1115/1.3269358.
FREE TO VIEW
Abstract
Commentary by Dr. Valentin Fuster
J. Vib., Acoust., Stress, and Reliab. 1986;108(3):386-387. doi:10.1115/1.3269359.
FREE TO VIEW
Abstract
Commentary by Dr. Valentin Fuster

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