Damage Hypotheses Research Articles

Bayesian damage localization and identification based on a transient wave propagation model for composite beam structures

This paper proposes the use of a physics-based Bayesian framework for the localization and identification of damage in composite beam structures using ultrasonic guided-waves. The methodology relies on a transient wave propagation model based on wave and finite element scheme that efficiently provides time-domain signals that are compared with the ultrasonic measurements within a multilevel Bayesian framework. As a key contribution, the proposed methodology enables the localization and identification of damage using just the signals without any baseline comparison or further transformation, hence reducing additional sources of uncertainty. The proposed Bayesian approach allows (1) the localization of the defect, and (2) the identification of different candidate damage hypotheses and their ranking based on probabilities that measure their relative degree of belief. The methodology is illustrated in carbon fiber reinforced polymer beams with different layups. An investigation into how the measurement noise can impact the identified damage properties is also provided. The results show the effectiveness and efficiency of the proposed approach in reconstructing and identifying different types of damage in long and complex composite beams at a relatively low computational cost.

Erosion Damage to Impeller of Welding Fume Extraction System

Abstract Even very simple cases of component failure can represent an enrichment for this section Failure Analysis. Besides the instructive value of an easily understandable content, they allow those failure analysts becoming acquainted with the field to gradually get to know the most important material-related mechanisms governing component failure cases. A look back by the authors on the section Failure Analysis of Practical Metallography cases revealed only one single erosion failure case in the past 10 years. It won't therefore do any harm to address this interesting failure mechanism once again. The erosion failure of a fan impeller presented in this article was very easily solved However, it was rather unexpected. Who would have considered it possible that an air extraction system in a factory workshop is subject to such high erosive distress? Hence, the main message of this short article is that the experts tasked with investigating the component failures should be very thorough and propose all sorts of damage hypotheses, sometimes even those which, at first glance, appear unlikely, and may only reject them when the examination results indicate the contrary.

43. Cell-based modeling of mechanical and chemical stress in tissues during cryoprotocols

Since Mazur’s work a half century ago, modeling of the biophysical processes of single cell cryopreservation has been successful in providing a theoretical groundwork for cryopreservation induced damage hypotheses. Important contributions have included both biophysical explanations of osmotic damage during CPA equilibration due to too aggressive or overly conservative equilibration strategies and estimation of cell injury due to intracellular ice formation through simple or complex ice-growth models. Follow up work by Mazur, Liebo and Chu presented the archetypical single cell protocol optimization using modeling, and subsequent investigators have for the most part followed in their footsteps with more sophisticated models of mass transport, cell damage and ice growth. Expanding on this work, a number of investigators have modeled unique damage pathways for cryopreserved tissues, raising important and challenging questions while providing steps towards optimal protocols. Models have included spatially dependent heat and mass transport, solidification fronts, and thermal and mechanical stresses, and a few models have combined tissue level transport with cell level damage estimators in sparsely celled articular cartilage and in simple spherically symmetrical tissue types. Most tissue modeling paradigms are cell unaware until modeling is complete: either cells are ignored in a continuum hypothesis, or are overlaid in a one-way model of tissue level transport to cell interaction. This approach precludes modeling a number of important cryobiological endpoints that are well understood at the single cell level including cell-to-cell mass transport, intercellular ice propagation, and strains on intercellular adhesion. As computational capabilities increase, cell- or agent-based multiscale modeling paradigms are becoming more realistic for understanding cell interactions, growth, and death in vivo. In these models cell interactions with their environment including cell–cell adhesive forces, transport, and growth and death through a number of mechanisms can be modeled in conjunction with classical heat and mass transport of critical solutes. Importantly from the cryobiological perspective, this approach allows modeling of cell-level tissue damage due to osmotic volume regulation, cell-to-cell ice propagation, and excitingly, the impacts of accumulated damage due to the cryopreservation process on post implantation survival at the single cell level via modeling of apoptotic, necrotic and other pathways. Here we summarize classical tissue cryopreservation modeling and successful approaches to individual cell damage modeling and optimization, and present our vision for the future of tissue and organ cryopreservation modeling and optimization.

Liquation Cracks in Hot Upset Low Alloy Steel Screw Heads

Abstract A thermally upset screw head had numerous cracks at the intersection screw head / screw shaft. The screw consisted of steel that usually does not tend to hot crack. The screw failed when tightening it by applying a torque lower than the nominal torque. The screw head was simply sheared off. A hot crack has clearly been identified as damage-causing mechanism of the material, or, more precisely, liquation cracks. Other damage hypotheses such as liquid metal induced stress corrosion cracking have reliably been excluded in the course of examinations. The material used was 1.7711, 40CrMoV4–6, a material especially used for creep resistant fasteners such as screws and nuts for operating temperatures up to 540°C. This material belongs to the group of low alloy chromium molybdenum vanadium steels. It is typically used in the tempered condition. In Europe, it corresponds to standard EN 10269. In the USA, this steel is known as ASTM A193 GR B16.

Reproductive Benefit of Oxidative Damage: An Oxidative Stress “Malevolence”?

High levels of reactive oxygen species (ROS) compared to antioxidant defenses are considered to play a major role in diverse chronic age-related diseases and aging. Here we present an attempt to synthesize information about proximate oxidative processes in aging (relevant to free radical or oxidative damage hypotheses of aging) with an evolutionary scenario (credited here to Dawkins hypotheses) involving tradeoffs between the costs and benefits of oxidative stress to reproducing organisms. Oxidative stress may be considered a biological imperfection; therefore, the Dawkins' theory of imperfect adaptation of beings to environment was applied to the role of oxidative stress in processes like famine and infectious diseases and their consequences at the molecular level such as mutations and cell signaling. Arguments are presented that oxidative damage is not necessarily an evolutionary mistake but may be beneficial for reproduction; this may prevail over its harmfulness to health and longevity in evolution. Thus, Dawkins' principle of biological “malevolence” may be an additional biological paradigm for explaining the consequences of oxidative stress.

Structural damage identification using co-evolution and frequency response functions

A new damage identification strategy is presented in which damage scenarios and optimal tests are searched simultaneously. The proposed strategy, called Estimation-Exploration Algorithm (EEA), is based on co-evolutionary principles. Co-evolution is a biological process where populations of interacting individuals challenge each other in an ongoing cycle of adaptation. In EEA, a population of damage hypotheses evolves to predict physical tests that have been performed on a structure, while tests evolve to create discrepancy among current damage hypotheses that can explain the observed data. This co-evolutionary approach leads to physical experiments that carry optimal information and results in a fewer number of tests needed for the correct identification of the current damage state of a structure. EEA was introduced by the authors in the context of static testing and is extended in this work to steady-state dynamics. In this context, changes in frequency response functions are used to locate and quantify damage, while structural tests are defined by the location of excitation forces and sensors position. This work shows that EEA is a feasible methodology to alleviate the ill-posedness of inverse damage detection problems by providing an intelligent strategy for selecting tests that maximize information. Copyright © 2007 John Wiley & Sons, Ltd.

Damage Identification Using Sensitivity-Enhancing Control and Identified Models

This paper investigates a coherence approach for locating structural damage using modal frequencies and transfer function parameters identified from input-output data using Observer/Kalman filter identification (OKID). Autonomous damage identification using such forward methods generally require (i) a structural model by which to relate measured and predicted modal properties induced by damage, and (ii) good sensitivity of modal parameter changes to damage states. Using the coherence approach, a damage parameter vector comprised of a finite set of modal frequencies and transfer function parameters is hypothesized for each damage case using either identified or analytic structural models. Measured parameter vectors are extracted from experimental input-output data for a damaged structure using OKID and are compared to hypotheses to determine the most likely damage state. The richness of the parameter vector set, which is comprised of high-quality frequency measurements and lower-quality transfer function parameters, is evaluated in order to determine the ability to uniquely localize damage. The method is evaluated experimentally using a three-degree-of-freedom torsional system and a space-frame truss. Damage parameter hypotheses are generated from a model of the healthy structure developed by system identification in the torsional system, and an analytic model is used to generate damage hypotheses for the truss structure. Feedback control laws enhance the parameter vectors by including closed-loop modal frequencies in order to reduce noise sensitivity and improve uniqueness of parameter vector hypotheses to each damage case. Results show improvements in damage identification using damage parameter vectors comprised of open- and closed-loop modal frequencies, even when model error exists in structural models used to form damage parameter vector hypotheses.

Fatigue test and reliability design of gears

Fatigue life of gearwheels made from commonly used gear materials has been studied extensively. The results can be expressed in the form of S-N curves, and more recently also in R-S-N curves. For a typical gear application, the load spectrum representing gear service loads can be obtained from industrial standard data or through direct measurement. Based on the above load spectrum and R-S-N curves, the reliability design of gears can be carried out by applying one of the cumulative damage hypotheses. This paper investigates the applicability of the Palmgren-Miner hypothesis and two other modified linear cumulative damage hypotheses in gear reliability design through experimental tests. The results show some improvement of the calculated lifetimes with the modified hypotheses. In the higher reliability range, however, a relatively significant discrepancy between the experimental and calculated lifetimes still exists. Hypotheses with progressive damage accumulation are required to give more precise lifetime predictions in this important range.

Effects of Lightning on Concrete

Possible lightning damage to a concrete farm silo in northeast Iowa prompted a research study of the damaging effects of lightning strokes on concrete. Lightning damage to concrete was studied by reviewing other writings on damaging effects and by completing simulated lightning strokes on concrete samples. Two sets of experiments were carried out. The damage caused by the simulated lightning strokes varied in intensity. Photos of the damaged samples are included in this paper. Correlations between observed damage and damage hypotheses are presented.