Failure Mechanisms in Sand over a Deep Active Trapdoor

An experimental testing program was undertaken to investigate failure mechanisms induced by the active movement of a deep rectangular trapdoor underlying a granular soil. Reduced-scale models were tested under normal gravity as well as under an increased gravitational field using a centrifuge facility. Some models were used to evaluate the performance of both flexible and rigid pipes undergoing a localized loss of support. Failure mechanisms in the longitudinal direction of the models were characterized by a single, well-defined failure surface that developed within the limits of the trapdoor. However, failure mechanisms in the transverse direction of the models were characterized by multiple failure surfaces extending outside the limits of the trapdoor. Significant dilation of the soil located immediately above the trapdoor was identified in the failure of the models. The pattern of the failure mechanisms was found to be affected by the stress level and backfill density. Higher stress levels were found to lead to well-developed failure zones. The influence of backfill density was found to be more relevant in models involving flexible pipes. Pipes embedded within loose backfill were severely damaged after loss of support, while pipes embedded in dense backfill experienced negligible deformations. These results indicate that damage to pipelines caused by ground loss of support can be significantly minimized by controlling the compaction of the fill.

Post-failure behaviour of impulsively loaded circular plates

The dynamic plastic response of a simply supported circular plate is analysed. Emphasis is given to the plate behaviour after it has broken free from the supports due to a local material failure. The theoretical rigid plastic analysis predicts various features of the response such as the time to failure, residual kinetic energy and the critical velocity at failure. The residual kinetic energy of the plate could be significant enough to cause secondary impact damage. It is shown that the shape of the plate changes after breaking free from the supports, which is important for forensic investigations. The solution for various cases were proven to be exact in the context of the upper and lower bounds theorems of the theory of plasticity. (C) 2009 Elsevier Ltd. All rights reserved.

Failure analysis of belt/roll tribological pair used for the production of eucalypt fiber panels

The premature failure of a large agglomeration machine used for the annual production of 360,000 m(3) of eucalypt fiber panels was investigated to identify the nucleation and growth mechanisms of cracking in PH stainless steel belts (126 m x 2.9 m x 3.0 mm). These belts are used to compress a cushion composed of eucalyptus fibers and glue, being the pressure transmitted from the pistons by the action of numerous case-hardening steel rolls. Examination of the belt working interfaces (belt/rolls and belt/eucalypt fibers) indicated that the main cracking was nucleated on the belt/roll interface and that there is a clear relationship between the crack nucleation and the presence of superficial irregularities, which were observed on the belt/roll working surface. Used rolls showed the presence of perimetric wear marks and 2 mu m silicon-rich encrusted particles (identified as silicon carbide). Lubricant residues contained the presence of helicoidal wires, which were originated by the release of the stainless steel cleaning brush bristles, and 15 mu m diameter metallic particles, which were generated by material detachment of the belt. The presence of foreign particles on the tribological interface contributed to an increase of the shear stresses at the surfaces and, consequently, the number of the contact fatigue crack nucleation sites in the belt/roll tribo-interface. The cracking was originated on the belt/roll interface of the stainless steel belt by a mixed rolling/slip contact fatigue mechanism, which promoted spalling and further nucleation and growth of conventional fatigue cracks. Finally, the system lubrication efficiency and the cleaning procedure should be optimised in order to increase the life expectancy of the belt. (c) 2006 Elsevier Ltd. All rights reserved.

Fretting fatigue in overhead conductors: Rig design and failure analysis of a Grosbeak aluminium cable steel reinforced conductor

The performance optimisation of overhead conductors depends on the systematic investigation of the fretting fatigue mechanisms in the conductor/clamping system. As a consequence, a fretting fatigue rig was designed and a limited range of fatigue tests was carried out at the middle high cycle fatigue regime in order to access an exploratory S-N curve for a Grosbeak conductor, which was mounted on a mono-articulated aluminium clamping system. Subsequent to these preliminary fatigue tests, the components of the conductor/clamping system, such as ACSR conductor, upper and lower clamps, bolt and nuts, were subjected to a failure analysis procedure in order to investigate the metallurgical free variables interfering on the fatigue test results, aiming at the optimisation of the testing reproducibility. The results indicated that the rupture of the planar fracture surfaces observed in the external At strands of the conductor tested under lower bending amplitude (0.9 mm) occurred by fatigue cracking (I mm deep), followed by shear overload. The V-type fracture surfaces observed in some At strands of the conductor tested under higher bending amplitude (1.3 mm) were also produced by fatigue cracking (approximately 400 mu m deep), followed by shear overload. Shear overload fracture (45 degrees fracture surface) was also observed on the remaining At wires of the conductor tested under higher bending amplitude (1.3 mm). Additionally, the upper and lower Al-cast clamps presented microstructure-sensitive cracking, which was folowed by particle detachment and formation of abrasive debris on the clamp/conductor tribo-interface, promoting even further the fretting mechanism. The detrimental formation of abrasive debris might be inhibited by the selection of a more suitable class of as-cast At alloy for the production of clamps. Finally, the bolt/nut system showed intense degradation of the carbon steel nut (fabricated in ferritic-pearlitic carbon steel, featuring machined threads with 190 HV), with intense plastic deformation and loss of material. Proper selection of both the bolt and nut materials and the finishing processing might prevent the loss in the clamping pressure during the fretting testing. It is important to control the specification of these components (clamps, bolt and nuts) prior to the start of large scale fretting fatigue testing of the overhead conductors in order to increase the reproducibility of this assessment. (c) 2008 Elsevier Ltd. All rights reserved.

Failure assessments of corroded pipelines with axial defects using stress-based criteria: Numerical studies and verification analyses

Conventional procedures used to assess the integrity of corroded piping systems with axial defects generally employ simplified failure criteria based upon a plastic collapse failure mechanism incorporating the tensile properties of the pipe material. These methods establish acceptance criteria for defects based on limited experimental data for low strength structural steels which do not necessarily address specific requirements for the high grade steels currently used. For these cases, failure assessments may be overly conservative or provide significant scatter in their predictions, which lead to unnecessary repair or replacement of in-service pipelines. Motivated by these observations, this study examines the applicability of a stress-based criterion based upon plastic instability analysis to predict the failure pressure of corroded pipelines with axial defects. A central focus is to gain additional insight into effects of defect geometry and material properties on the attainment of a local limit load to support the development of stress-based burst strength criteria. The work provides an extensive body of results which lend further support to adopt failure criteria for corroded pipelines based upon ligament instability analyses. A verification study conducted on burst testing of large-diameter pipe specimens with different defect length shows the effectiveness of a stress-based criterion using local ligament instability in burst pressure predictions, even though the adopted burst criterion exhibits a potential dependence on defect geometry and possibly on material`s strain hardening capacity. Overall, the results presented here suggests that use of stress-based criteria based upon plastic instability analysis of the defect ligament is a valid engineering tool for integrity assessments of pipelines with axial corroded defects. (C) 2008 Elsevier Ltd. All rights reserved.

Stress cracking and photodegradation behavior of polycarbonate. The combination of two major causes of polymer failure

This work investigates the effects of photodegradation on the environmental stress cracking resistance of polycarbonate (PC). Injection molded samples were exposed to the ultraviolet (UV) light for various times in the laboratory prior to solvent contact. The bars were then stressed with two different loads in a tensile testing machine under the presence of ethanol. During this period, the stress relaxation was monitored and, after unloading, the ultimate properties were evaluated. Complementary tests were done by size exclusion chromatography, UV-visible spectroscopy, scanning electron microscopy, and light microscopy. The results indicated that ethanol causes significant modification in PC, with extensive surface crazing as well as reduction in mechanical properties. The previous degraded samples showed a higher level of stress relaxation and a greater loss in tensile strength in comparison with the undegraded ones. The synergist action of photodegradation and stress cracking in PC may be a consequence of the chemical changes caused by oxidation.

The Kumaraswamy Weibull distribution with application to failure data

For the first time, we introduce and study some mathematical properties of the Kumaraswamy Weibull distribution that is a quite flexible model in analyzing positive data. It contains as special sub-models the exponentiated Weibull, exponentiated Rayleigh, exponentiated exponential, Weibull and also the new Kumaraswamy exponential distribution. We provide explicit expressions for the moments and moment generating function. We examine the asymptotic distributions of the extreme values. Explicit expressions are derived for the mean deviations, Bonferroni and Lorenz curves, reliability and Renyi entropy. The moments of the order statistics are calculated. We also discuss the estimation of the parameters by maximum likelihood. We obtain the expected information matrix. We provide applications involving two real data sets on failure times. Finally, some multivariate generalizations of the Kumaraswamy Weibull distribution are discussed. (C) 2010 The Franklin Institute. Published by Elsevier Ltd. All rights reserved.

Tests for the hysteresis hypothesis in Brazilian industrialized exports: A threshold cointegration analysis

This paper examines the hysteresis hypothesis in the Brazilian industrialized exports using a time series analysis. This hypothesis finds an empirical representation into the nonlinear adjustments of the exported quantity to relative price changes. Thus, the threshold cointegration analysis proposed by Balke and Fomby [Balke, N.S. and Fomby, T.B. Threshold Cointegration. International Economic Review, 1997; 38; 627-645.] was used for estimating models with asymmetric adjustment of the error correction term. Amongst sixteen industrial sectors selected, there was evidence of nonlinearities in the residuals of long-run relationships of supply or demand for exports in nine of them. These nonlinearities represent asymmetric and/or discontinuous responses of exports to different representative measures of real exchange rates, in addition to other components of long-run demand or supply equations. (C) 2007 Elsevier B.V. All rights reserved.

Expectation Propagation with Factorizing Distributions: A Gaussian Approximation and Performance Results for Simple Models

We discuss the expectation propagation (EP) algorithm for approximate Bayesian inference using a factorizing posterior approximation. For neural network models, we use a central limit theorem argument to make EP tractable when the number of parameters is large. For two types of models, we show that EP can achieve optimal generalization performance when data are drawn from a simple distribution.

Myocardial scintigraphy and clinical stratification as predictors of events in renal transplant candidates

Background: We tested the hypothesis that the universal application of myocardial scanning with single-photon emission computed tomography (SPECT) would result in better risk stratification in renal transplant candidates (RTC) compared with SPECT being restricted to patients who, in addition to renal disease, had other clinical risk factors. Methods: RTCs (n=363) underwent SPECT and clinical risk stratification according to the American Society of Transplantation (AST) algorithm and were followed up until a major adverse cardiovascular event (MACE) or death. Results: Of the 363 patients, 79 patients (22%) had an abnormal SPECT scan and 270 (74%) were classified as high risk. Both methods correctly identified patients with increased probability of MACE. However, clinical stratification performed better (sensitivity and negative predictive value 99% and 99% vs. 25% and 87%, respectively). High-risk patients with an abnormal SPECT scan had a modest increased risk of events (log-rank = 0.03; hazard ratio [HR] = 1.37; 95% confidence interval [95% CI], 1.02-1.82). Eighty-six patients underwent coronary angiography, and coronary artery disease (CAD) was found in 60%. High-risk patients with CAD had an increased incidence of events (log-rank = 0.008; HR=3.85; 95% CI, 1.46-13.22), but in those with an abnormal SPECT scan, the incidence of events was not influenced by CAD (log-rank = 0.23). Forty-six patients died. Clinical stratification, but not SPECT, correlated with the probability of death (log-rank = 0.02; HR=3.25; 95% CI, 1.31-10.82). Conclusion: SPECT should be restricted to high-risk patients. Moreover, in contrast to SPECT, the AST algorithm was also useful for predicting death by any cause in RTCs and for selecting patients for invasive coronary testing.

INTRACRANIAL PRESSURE MONITORING IN CHILDREN WITH FULMINANT HEPATIC FAILURE

Introduction. We describe a series of 10 children with intracranial hypertension complicating fulminant hepatic failure submitted to intracranial pressure (ICP) monitoring for intensive care an transplantation management. Patients and methods. Information from pediatrics patients acute liver failure admitted to our hospital was collected in a standard protocol form. We analyzed data from 10 patients, medium age 5.2 years old. In this period we studied aspects as ICP transducer used, number of days with ICP monitoring and complications of ICP monitoring. Results. Hepatitis A was diagnosed in five patients and hepatitis B in two cases. The initial ICP were 2 to 24 mmHg in transducer Seven patients died, four due to intracranial hypertension, included the patient operated for subdural hematoma, and three with transplantation failure. Only, a case of hematoma was verified. Conclusions. The application of ICP monitoring allows intensive care for aggressive ICP management. It can be used in children without adaptations. [REV NEUROL 2009: 48: 134-6]

The prevalence and significance of periodic leg movements during sleep in patients with congestive heart failure

The aim of this study was to evaluate (1) the prevalence of periodic leg movements during sleep (PLMs) in a consecutive sample of congestive heart failure (CHF) outpatients; (2) the presence of correlation between PLMs, subjective daytime sleepiness, and sleep architecture; and (3) the heart rate response to PLMs in CHF. Seventy-nine [50 men, age 59 +/- 11 years, body mass index (BMI) 26 +/- 5 kg/m(2)] consecutive adult stable outpatients with CHF [left ventricular ejection fraction (LVEF) 36 +/- 6%] were prospectively evaluated. The patients underwent assessment of echocardiography, sleepiness (Epworth Scale), and overnight in-lab polysomnography. Fifteen patients (19%) had PLM index > 5. These subjects were similar in sex distribution, BMI, subjective somnolence, LVEF, and apnea-hypopnea index (AHI), but were significantly older than subjects without PLMs. Sleep architecture was similar in subjects with and without PLMs. There was a small but significant elevation of heart rate after PLMs (80.1 +/- 9.4 vs. 81.5 +/- 9.2; p < 0.001). The cardiac acceleration was also present in absence of electroencephalogram activation. The prevalence of PLMs in consecutive sample of adult CHF outpatients was 19%. There were no differences in subjective daytime sleepiness, sleep architecture, AHI, and severity of CHF in subjects with and without PLMs. PLMs caused a small but statistically significant cardiac acceleration.

Long-Term Prospective, Randomized, Controlled Study Using Repetitive Education at Six-Month Intervals and Monitoring for Adherence in Heart Failure Outpatients The REMADHE Trial

Background-The effectiveness of heart failure disease management proarams in patients under cardiologists` care over long-term follow-up is not established. Methods and Results-We investigated the effects of a disease management program with repetitive education and telephone monitoring on primary (combined death or unplanned first hospitalization and quality-of-life changes) and secondary end points (hospitalization, death, and adherence). The REMADHE [Repetitive Education and Monitoring for ADherence for Heart Failure] trial is a long-term randomized, prospective, parallel trial designed to compare intervention with control. One hundred seventeen patients were randomized to usual care, and 233 to additional intervention. The mean follow-up was 2.47 +/- 1.75 years, with 54% adherence to the program. In the intervention group, the primary end point composite of death or unplanned hospitalization was reduced (hazard ratio, 0.64; confidence interval, 0.43 to 0.88; P=0.008), driven by reduction in hospitalization. The quality-of-life questionnaire score improved only in the intervention group (P<0.003). Mortality was similar in both groups. Number of hospitalizations (1.3 +/- 1.7 versus 0.8 +/- 1.3, P<0.0001), total hospital days during the follow-up (19.9 +/- 51 versus 11.1 +/- 24 days, P<0.0001), and the need for emergency visits (4.5 +/- 10.6 versus 1.6 +/- 2.4, P<0.0001) were lower in the intervention group. Beneficial effects were homogeneous for sex, race, diabetes and no diabetes, age, functional class, and etiology. Conclusions-For a longer follow-up period than in previous studies, this heart failure disease management program model of patients under the supervision of a cardiologist is associated with a reduction in unplanned hospitalization, a reduction of total hospital days, and a reduced need for emergency care, as well as improved quality of life, despite modest program adherence over time. (Circ Heart Fail. 2008;1:115-124.)

Hemodynamic response in one session of strength exercise with and without electrostimulation in heart failure patients: A randomized controlled trial

Background: Studies have investigated the influence of neuromuscular electrostimulation on the exercise/muscle capacity of patients with heart failure (HF), but the hemodynamic overload has never been investigated. The aim of our study was to evaluate the heart rate (HR), systolic and diastolic blood pressures in one session of strength exercises with and without neuromuscular electrostimulation (quadriceps) in HF patients and in healthy subjects. Methods: Ten (50% male) HF patients and healthy subjects performed three sets of eight repetitions with and without neuromuscular electrostimulation randomly, with one week between sessions. Throughout, electromyography was performed to guarantee the electrostimulation was effective. The hemodynamic variables were measured at rest, again immediately after the end of each set of exercises, and during the recovery period. Results: Systolic and diastolic blood pressures did not change during each set of exercises among either the HF patients or the controls. Without electrostimulation: among the controls, the HR corresponding to the first (85 +/- 13 bpm, p = 0.002), second (84 +/- 10 bpm, p < 0.001), third (89 +/- 17, p < 0.001) sets and recuperation (83 +/- 16 bpm, p = 0.012) were different compared to the resting HR (77 bpm). Moreover, the recuperation was different to the third set (0.018). Among HF patients, the HR corresponding to the first (84 +/- 9 bpm, p = 0.041) and third (84 +/- 10 bpm, p = 0.036) sets were different compared to the resting HR (80 +/- 7 bpm), but this increase of 4 bpm is clinically irrelevant to HF. With electrostimulation: among the controls, the HR corresponding to the third set (84 +/- 9 bpm) was different compared to the resting HR (80 +/- 7 bmp, p = 0.016). Among HF patients, there were no statistical differences between the sets. The procedure was well tolerated and no subjects reported muscle pain after 24 hours. Conclusions: One session of strength exercises with and without neuromuscular electrostimulation does not promote a hemodynamic overload in HF patients. (Cardiol J 2011; 18,1: 39-46)

VALIDATION OF THE LONDON CHEST ACTIVITY OF DAILY LIVING SCALE IN PATIENTS WITH HEART FAILURE

Background: The Minnesota Living with Heart Failure Questionnaire (MLHFQ) is a well-validated, commonly-used tool to assess quality of life in patients with heart failure. However, it lacks specific information concerning breathlessness during daily activities. Objective: To determine the validity of the London Chest Activity of Daily Living (LCADL) scale for use in patients with heart failure. Methods: Forty-seven patients with heart failure (57% males, mean age 50 years (standard deviation 9), mean left ventricle ejection fraction 29% (SD 6), New York Heart Association (NYHA) functional class I-III) were included. All subjects first performed a cardiopulmonary exercise test and then responded to the LCADL and the MLHFQ, with guidance from the same investigator. The re-test for the LCADL was applied one week later. Results: LCADL was correlated with MLHFQ (r=0.88; p < 0.0001). LCADL and MLHFQ were also correlated with exercise capacity (r=-0.75 and r=-0.73, respectively; both p < 0.0001). The LCADL was shown to be reproducible (r(i)=0.98). There was a significant difference (p < 0.05) in the LCADL scores between NYHA functional classes I and II, as well as classes I and III, hut not between classes II and III. Conclusion: The LCADL was shown to be a valid measurement of dyspnoea during daily activities in patients with heart failure. This scale could be an additional useful tool for the assessment of patients` dyspnoea during activities of daily living.