Cumulative spinal loading exposure methods for manual material handling tasks. Part 2: methodological issues and applicability for use in epidemiological studies

Objective: The goal of this paper is to review and discuss methodological issues related to cumulative spinal loading exposure assessment methods. Background: Research has indicated that there likely is an association between integrated spinal loading and lower back pain. A number of studies have been conducted to evaluate cumulative load; however, comparisons between studies is difficult due to the use of different methods for the assessment of cumulative spinal loading. Methods: A comprehensive electronic search was conducted to locate articles dealing with methods of cumulative spinal loading estimation. The articles were evaluated with respect to methods for obtaining postural data, methods for estimating spinal loads, methods for integrating loads over time and spinal load parameters to be measured. Results: Thirteen articles were located. A summary of the methods used to estimate cumulative spinal load is described and evaluated. Conclusions: There is a pressing need for integrated spinal loading methods that are reliable, valid and practical for use in large occupational epidemiological studies. A number of research needs were outlined aimed at improving the ability to use cumulative load to predict risk of low back disorders due to manual material handling.     

Multiaxial fatigue life prediction method based on path‐dependent cycle counting under tension/torsion random loading

A path‐dependent cycle counting method is proposed by applying the distance formula between two points on the tension‐shear equivalent strain plane for the identified half‐cycles first. The Shang–Wang multiaxial fatigue damage model for an identified half‐cycle and Miner's linear accumulation damage rule are used to calculate cumulative fatigue damage. Therefore, a multiaxial fatigue life prediction procedure is presented to predict conveniently fatigue life under a given tension and torsion random loading time history. The proposed method is evaluated by experimental data from tests on cylindrical thin‐walled tubes specimens of En15R steel subjected to combined tension/torsion random loading, and the prediction results of the proposed method are compared with those of the Wang–Brown method. The results showed that both methods provided satisfactory prediction.     

Human posture simulation to assess cumulative spinal load due to manual lifting. Part I: methods

The estimation of cumulative spinal load (CSL) resulting from exposure to manual materials handling (MMH) may provide a sensitive method for assessing the risk of highly varying exposures. This article reports on a CSL method that involves human posture simulation of workers from videotape in order to assess spinal load exposures due to MMH. The proposed method appears to be sensitive to different durations of exposure, easy to use and useful for assessing jobs with a high degree of variability in task characteristics between lifts. Although the method remains to be validated, it appears to be a useful addition to the range of tools available for assessing manual lifting exposures in worksite-based epidemiologic studies. Ergonomic methods are lacking for assessing highly variable MMH tasks, such as tasks found in warehousing. The existing methods do not include sufficient factors to account for variable exposure patterns or tasks with highly variable task characteristics, such as varying load weights and lift geometries. The CSL assessment method described in this article may provide a way to evaluate these types of tasks in order to assess the overall risk of workers developing work-related musculoskeletal disorders.     

Late detection of hazards in traffic: A matter of response bias?

In this study, results from two different hazard perception tests are presented: the first one is a classic hazard-perception test in which participants must respond – while watching real traffic video scenes – by pressing the space bar in a keyboard when they think there is a collision risk between the camera car and the vehicle ahead. In the second task we use fragments of the same scenes but in this case they are adapted to a signal detection task – a ‘yes’/‘no’ task. Here, participants – most of them, University students – must respond, when the fragment of the video scene ends, whether they think the collision risk had started yet or not. While in the first task we have a latency measure (the time necessary for the driver to respond to a hazard), in the second task we obtain two separate measures of sensitivity and criterion. Sensitivity is the driver’s ability to discriminate in a proper way the presence vs. absence of the signal (hazard) while the criterion is the response bias a driver sets to consider that there is a hazard or not. His/her criterion could be more conservative – the participant demands many cues to respond that the signal is present, neutral or even liberal – the participant will respond that the signal is present with very few cues. The aim of the study is to find out if our latency measure is associated with a different sensitivity and/or criterion. The results of the present study show that drivers who had greater latencies and drivers who had very low latencies yield a very similar sensitivity mean value. Nevertheless, there was a significant difference between these two groups of drivers in criterion: those drivers who had greater latencies in the first task were also more conservative in the second task. That is, the latter responded less frequently that there was danger in the sequences. We interpret that greater latencies in our first hazard perception test could be due to a stricter or more conservative criterion, rather than a low sensitivity to perceptual information for collision risk. Drivers with a more conservative criterion need more evidences of danger, thus taking longer to respond.     

On the relation between rigid-plastic and elastic-plastic predictions of response to pulse loading

Using a simple model, comparisons are shown between the predictions of elastic-plastic and rigid-plastic analyses as to the permanent displacements due to pulse loading. Several pulse shapes are considered, and the comparisons are made over a large range of the ratio τ/T (pulse duration time/natural period of the structure). When the rise time of the pulse is not zero, these show a wavy character that was not seen in earlier comparisons of this type, where smaller ranges were used. Thus the two predictions are found to be very close at regular intervals, while the rigid-plastic prediction has negative (unconservative) errors in between, relative to the elastic-plastic one. These errors may be large even though the plastic deformation greatly exceeds the elastic displacement at yield. The ‘energy ratio’ criterion for validity of rigid-plastic analysis must be supplemented, for ‘long’ pulses, by consideration of the effect of pulse duration. The waviness of the elastic-plastic spectral plots is explained in terms of the similar shapes of the ‘dynamic amplification’ spectra of wholly elastic shock analysis.     

On‐line reliability estimation for individual components using statistical degradation signal models

With very few exceptions, most contemporary reliability engineering methods are geared towards estimating a population characteristic(s) of a system, subsystem or component. The information so extracted is extremely valuable for manufacturers and others that deal with product in relatively large volumes. In contrast, end users are typically more interested in the behavior of a ‘particular’ component used in their system to arrive at optimal component replacement or maintenance strategies leading to improved system utilization, while reducing risk and maintenance costs. The traditional approach to addressing this need is to monitor the component through degradation signals and ‘classifying’ the state of a component into discrete classes, say ‘good’, ‘bad’ and ‘in‐between’ categories. In the event, one can develop effective degradation signal forecasting models and precisely define component failure in the degradation signal space, then, one can move beyond the classification approach to a more vigorous reliability estimation and forecasting scheme for the individual unit. This paper demonstrates the feasibility of such an approach using ‘general’ polynomial regression models for degradation signal modeling. The proposed methods allow first‐order autocorrelation in the residuals as well as weighted regression. Parametric bootstrap techniques are used for calculating confidence intervals for the estimated reliability. The proposed method is evaluated on a cutting tool monitoring problem. In particular, the method is used to monitor high‐speed steel drill‐bits used for drilling holes in stainless‐steel metal plates. A second study involves modeling and forecasting fatigue‐crack‐growth data from the literature. The task involved estimating and forecasting the reliability of plates expected to fail due to fatigue‐crack‐growth. Both studies reveal very promising results. Copyright © 2002 John Wiley & Sons, Ltd.     

Measurement for evaluating the learnability and resilience of methods of cognitive work

Some experiments on human–computer interaction are aimed at evaluating hypotheses concerning cognitive work. Other experiments are intended to evaluate the software tools that shape the cognitive work. In both cases, effective experimentation is premised on the control and factorial analysis of sources of variability. This entails programmes of experimentation. However, sociotechnical systems are generally a ‘moving target’ in terms of the pace of change. The objective of this study was to create a general approach to experimental design and the measurement of cognitive work that can satisfy the requirements for experimentation and yet can also provide a ‘fast track’ to the evaluation of software-supported cognitive work. A measure called i-bar is presented, which is the inverse of the mid-range. The statistic is derived from data on trials-to-criterion in tasks that require practice and learning. This single measure is interpreted as a conjoint measurement scale, permitting: (a) evaluation of sensitivity of the principal performance measure (which is used to set the metric for trials to criterion); (b) evaluation of the learnability of the work method (i.e. the goodness of the software tool); (c) evaluation of the resilience of the work method. It is shown that it is possible to mathematically model such order statistics and derive methods for estimating likelihoods. This involves novel ways of thinking about statistical analysis for discrete non-Gaussian distributions. The idea and method presented herein should be applicable to the study of the effects of any training or intervention, including software interventions designed to improve legacy work methods and interventions that involve creating entirely new cognitive work systems.     

Life assessment for metallic materials with the use of the strain criterion for low-cycle fatigue

In this paper the investigation results for verification of the developed low-cycle failure criterion as applied to multiaxial (non-proportional) loading are presented. Several approaches for determination of the parameter of sensitivity to the cycle non-proportionality are reviewed. Simple phenomenological models are proposed for determining the material parameters and constants of the criterion relationship. A method for describing Morrow’s cyclic diagrams using a material static stress–strain diagram and one base experiment under uniaxial cyclic loading on the limited number of cycles has been developed. For the verification of the proposed models and strain criterion life calculation of an aircraft structural element is executed. For this purpose FEM analysis, improvement of a nonlinear rule of damages accumulation and the concept of critical distance for determination of damage to a local concentrator zone was used. Conservative results of life forecasting which well correlate with experimental data are received.     

Life prediction based on weight‐averaged maximum shear strain range plane under multiaxial variable amplitude loading

Based on Wang and Brown's reversal counting method, a new approach to the determination of the critical plane is proposed by the defined plane with a weight‐averaged maximum shear strain range under multiaxial variable amplitude loading. According to the determined critical plane, a detailed procedure of multiaxial fatigue life prediction is introduced to predict lives in the low‐cycle multiaxial fatigue regime. The proposed approach is verified by two multiaxial fatigue damage models and Miner's linear cumulative damage law. The results showed that the proposed approach can effectively predict the orientation of the failure plane under multiaxial variable amplitude loading and give a satisfactory life prediction.     

A simple energy‐based model for nonproportional low‐cycle multiaxial fatigue life prediction under constant‐amplitude loading

From the literature concerning the traditional nonproportional (NP) multiaxial cyclic fatigue prediction, special attentions are usually paid to multiaxial constitutive relations to quantify fatigue damage accumulation. As a result, estimation of NP hardening effect decided by the entire history path is always proposed, which is a challenging and complex task. To simplify the procedure of multiaxial fatigue life prediction of engineering components, in this paper, a novel effective energy parameter based on simple material properties is proposed. The parameter combines uniaxial cyclic plastic work and NP hardening effects. The fatigue life has been assessed based on traditional multiaxial fatigue criterion and the proposed parameter, which has been validated by experimental results of 316 L stainless steel under different low‐cycle loading paths.     

A modified normal strain ratio fatigue life model based on the hybrid approach of critical plane and crystallographic slip theory

Based on the method combining the critical plane with crystallographic slip theory, an anisotropic low cycle fatigue life model is proposed to reflect the effects of orientation dependence and damage factors on fatigue life. According to this method, the crystallographic slip plane is adopted as the critical plane by searching for 30 potential slip systems. In addition, considering the effects of normal strain and strain ratio on fatigue failure, the normal strain ratio is introduced into model and regression model is obtained by fitting method. The proposed model is verified by estimating the low cycle fatigue lives of single crystal nickel–based superalloys PWA1480, CMSX‐2 and DD3 for different loading conditions. The results show that the proposed model is applicable for more complicated loading situations and give a higher prediction accuracy compared to Sun's model.     

A no reference quality metric to measure the blocking artefacts for video sequences

The need to measure video quality arises in the development of video equipment and in the delivery and storage of video and image information. In this paper, we propose a new perceptually significant video quality metric to estimate the effect of block coding for standards H.264 AVC and MPEG2. Our method operates in the spatial domain and does not require a high complexity of computation. We evaluate the performance of the proposed method by using three sequences CIF ‘common intermediate file’ with different compression rate. We compare it with Suthaharan’s and MSU’s techniques by using ‘LIVE’ and ‘IVP’ databases. Results indicate that the proposed method outperforms Suthaharan’s and MSU techniques in H264 coder. They also indicate that our method is more effective than MSU’s and Suthaharan’s techniques for the H.264 AVC standards with the Spearman Rank Order Correlation Coefficient.     

Parameter determination of Chaboche kinematic hardening model using a multi objective Genetic Algorithm

Chaboche model is a powerful tool to evaluate the cyclic behavior under different loading conditions using kinematic hardening theory. It can also predict the ratcheting phenomenon. To predict the ratcheting, it is required to determine the material parameters under strain control conditions. Although, these parameters can model the hysteresis loop fairly accurately, their ratcheting prediction does not have the same quality. A set of material parameters that could accurately predict both ratcheting and hysteresis loop is of great importance. The available models, generally for low cycle fatigue, are mostly complex and nonlinear. Therefore, an optimization procedure can be used for parameter determination and consequently improving the prediction of these models.Genetic Algorithm is a numerical approach for optimization of nonlinear problems. Using a multi objective Genetic Algorithm for Chaboche model, a set of parameters was obtained which improved both ratcheting prediction and hysteresis loop model. Two fitness functions were used for this approach. The proposed model was verified using Hassan and Corona’s experimental data conducted on CS 1026 low carbon steel. The model indicated a very good agreement in the case of uniaxial loading with the experimental data. The results of proposed model for biaxial loading histories are similar to the model by Hassan and his co-workers.     

A PROBABILISTIC APPROACH TO FAILURE PREDICTION OF FRP LAMINATED COMPOSITES

The failure of fiber-reinforced plastic (FRP) laminated composites is examined, taking into account statistical aspects of the basic strength properties of the material The purpose of the analysis is to establish simple rules and methodologies for failure prediction under specific reliability requirements. An analytical approach is developed for the prediction of failure under general in-plane loading, consisting of a functional expansion technique for the derivation of the cumulative distribution Junction of the failure condition. A semideterministic method is also examined, according to which the failure criterion is used in the usual deterministic way but with the basic strength values at a certain reliability level. The two methods are gradually built up by first examining their effectiveness on the failure prediction of unidirectional laminae. Results for the case of a unidirectional laminate are presented for the case of off-axis layers, and both methods are shown to yield results in fair agreement with Monte Carlo simulated ones and experimental data. For the more general case of multilayered composites, comparison of theoretical results with numerical simulated data and experimental ones reveals that both methods hold their effectiveness.     

Development of a human information processing model for cognitive task analysis and design

High costs and long cycle times of software development are factors hindering the analysis and design of the complete cognitive aspects related to task performances. Reusable software has been proposed as a solution to the problem of high software development and maintenance costs. One of the paradigms for reusable software, object-oriented modelling, has emerged as an important method for specifying, creating and reusing software modules. Using Unified Modelling Language, this paper develops an object-oriented cognitive task analysis and design (OOCTAD) model based on human information-processing theory. First, human task performance-related cognitive aspects are classified into modules and logically linked together; secondly, cognitive aspects within these modules were further decomposed into packages and classes based on object-oriented technology. Finally, one case study was presented to compare and contrast different cognitive analysis models to illustrate the advantages of the OOCTAD model developed in the current research over the other five cognitive task analysis models. These reusable classes in the OOCATD model were shown to be reused to reduce software development costs and cycle times for cognitive task analysis and design. The current research should be of use to both developers and users of cognitively based tasks, systems and tools and researchers and practitioners in the broader discipline of cognitive tasks design and analysis.     

单输入多输出耦合设计任务二阶段迭代模型研究

产品开发过程中单输入多输出耦合设计任务间存在复杂的信息依赖关系。采用单阶段方法的任务执行方式时,因所执行的任务数量多并且需传递的信息量大,致使任务间存在的复杂信息关系难以被理清,从而导致任务执行过程中的方案分配不够合理,任务间的迭代返工次数过多,产品开发周期过长。针对这些问题,在深入分析单输入多输出耦合设计任务单阶段迭代模型的基础上,提出了一种任务迭代过程中的信息处理策略,并构建了一种单输入多输出耦合设计任务的二阶段迭代模型及其求解执行时间的数学模型。应用该数学模型,可以计算得到最佳二阶段设计任务分配方案。以某发动机开发项目为例,进行了该方法的应用分析。研究表明,采取二阶段迭代模型,任务迭代执行时间比单阶段短,并且通过合理分配在1,2两个阶段执行的任务,能够获得最短的二阶段任务迭代执行时间。该方法根据任务间不同的信息关系选择合适的任务迭代模型,能够有效缩短产品开发周期,可为产品设计人员在产品开发过程中选择合理的任务执行方式提供一定的理论参考。     

Stepped‐isothermal fatigue analysis of engine piston

Stepped‐isothermal fatigue failure is the main failure mechanism of modern engine pistons under bench reliability test condition. This paper presents a methodology for stepped‐isothermal fatigue analysis of engine pistons, which consists of a fatigue criterion, evaluation of temperature and stress distribution by finite element analysis and the final life prediction. The major character of the methodology is the fatigue definition of engine pistons with respect to engine load change cycle and a damage‐based fatigue criterion accounting for the nonlinear creep–fatigue damage. Taking as an example, the fatigue life of an engine piston was predicted by the proposed analysis procedures. The analysis results showed that the most critical area was located in the throat edge. Moreover, the proposed methodology can give a relatively accurate and reasonable life prediction for an engine piston under the loading condition of bench reliability test, with a benefit of decreasing the needed component's reliability tests and design time.     

Probabilistic failure prediction for FRP composites

Results are presented from a theoretical study on failure-locus prediction for unidirectional FRP laminae under complex in-plane loading, taking into account statistical aspects of the basic strengths of the material. The purpose of the analysis is to establish simple rules and methodologies for failure prediction under specific reliability requirements. Therefore, the problem one is faced with is the definition of the cumulative distribution function (CDF) of the failure condition if the respective CDFs of the basic material strengths are known by experiment. To this end, two analytical approaches, namely a functional expansion technique and the introduction of Pearson’s semi-empirical distribution function, were developed and implemented in software. Both methods were shown to predict satisfactory results compared with Monte Carlo simulated ones and experimental data, wherever available. Finally, a semi-deterministic approach was examined according to which the failure criterion is used in the usual deterministic way but with basic strength values of a certain reliability level. Results from this simple and fast method were found in good agreement with those derived by expensive pure statistical methods or numerically simulated ones and experimental data.     

Low-cycle fatigue life assessment for gas turbine engine disks under flight cycle conditions

We address the effects of the actual flight cycle on durability of gas turbine engine disks under low-cycle fatigue. An approach is proposed which improves reliability of life cycle prediction owing to schematization of flight cycle with a criterion for reaching the maximum intensity of total strain range. Contribution of subcycles to the cumulative damage is demonstrated. __________ Translated from Problemy Prochnosti, No. 1, pp. 129–133, January–February, 2009.     

A Novel Method to Predict the Low-Cycle Fatigue Life

Since fatigue failure commonly occurs in mechanical equipment, the prediction of the fatigue life is important to ensure safety in the running cycle of production. In this paper, a method is proposed to predict the low-cycle fatigue life. The accuracy of the proposed method is compared to the strain energy criterion and Coffin–Manson/Basquin equation with three different materials. The results indicate that accuracy of the proposed method is similar to the strain energy criterion and Coffin–Manson/Basquin equation in predicting the low-cycle fatigue life.