Effects Of Overloading Research Articles

Investigating the effects of preliminary overloading and fatigue on the mechanical strength and fractographic characteristics of CuSn7Zn4Pb7 bronze alloy fractures

This study presents the outcomes of experimental research designed to explore the effects of plastic deformation on the tensile strength and torsional fatigue life of the CuSn7Zn4Pb7 bronze alloy. The primary objective was to understand how plastic deformation impacts these critical mechanical properties of the alloy. The study aimed to determine the nature of damages and attempt to systematise them. Various combinations of loads and material microstructure play a decisive role in the propagation of fatigue cracks. Therefore, in the study, the microstructure of the analysed material, the determination of its chemical composition, and its compliance with relevant material standards were presented. Additionally, microscopic images of fracture surfaces, along with fatigue crack analysis and determining the presence of the fatigue and residual zones, were provided.

Bio-orthogonal Click Chemistry Methods to Evaluate the Metabolism of Inflammatory Challenged Cartilage after Traumatic Overloading.

During traumatic joint injuries, impact overloading can cause mechanical damage to the cartilage. In the following inflammation phase, excessive inflammatory cytokines (e.g., interleukin-1β (IL-1β)) can act on chondrocytes, causing over-proliferation, apoptosis, and extracellular matrix (ECM) degradation that can lead to osteoarthritis. This study investigated the combined effects of traumatic overloading and IL-1β challenge on the metabolic activities of chondrocytes. Bovine cartilage explants underwent impact overloading followed by IL-1β exposure at a physiologically relevant dosage (1 ng/mL). New click chemistry-based methods were developed to visualize and quantify the proliferation of in situ chondrocytes in a nondestructive manner without the involvement of histological sectioning or antibodies. Click chemistry-based methods were also employed to measure the ECM synthesis and degradation in cartilage explants. As the click reactions are copper-free and bio-orthogonal, i.e., with negligible cellular toxicity, cartilage ECM was cultured and studied for 6 weeks. Traumatic overloading induced significant cell death, mainly in the superficial zone. The high number of dead cells reduced the overall proliferation of chondrocytes as well as the synthesis of glycosaminoglycan (GAG) and collagen contents, but overloading alone had no effects on ECM degradation. IL-1β challenge had little effect on cell viability, proliferation, or protein synthesis but induced over 40% GAG loss in 10 days and 61% collagen loss in 6 weeks. For the overloaded samples, IL-1β induced greater degrees of degradation, with 68% GAG loss in 10 days and 80% collagen loss in 6 weeks. The results imply a necessary immediate ease of inflammation after joint injuries when trauma damage on cartilage is present. The new click chemistry methods could benefit many cellular and tissue engineering studies, providing convenient and sensitive assays of metabolic activities of cells in native three-dimensional (3D) environments.

A Study on the Effects of Cognitive Overloading and Distractions on Human Movement During Robot-Assisted Dressing.

For robots that can provide physical assistance, maintaining synchronicity of the robot and human movement is a precursor for interaction safety. Existing research on collaborative HRI does not consider how synchronicity can be affected if humans are subjected to cognitive overloading and distractions during close physical interaction. Cognitive neuroscience has shown that unexpected events during interactions not only affect action cognition but also human motor control Gentsch et al. (Cognition, 2016, 146, 81–89). If the robot is to safely adapt its trajectory to distracted human motion, quantitative changes in the human movement should be evaluated. The main contribution of this study is the analysis and quantification of disrupted human movement during a physical collaborative task that involves robot-assisted dressing. Quantifying disrupted movement is the first step in maintaining the synchronicity of the human-robot interaction. The human movement data collected from a series of experiments where participants are subjected to cognitive loading and distractions during the human-robot interaction, are projected in a 2-D latent space that efficiently represents the high-dimensionality and non-linearity of the data. The quantitative data analysis is supported by a qualitative study of user experience, using the NASA Task Load Index to measure perceived workload, and the PeRDITA questionnaire to represent the human psychological state during these interactions. In addition, we present an experimental methodology to collect interaction data in this type of human-robot collaboration that provides realism, experimental rigour and high fidelity of the human-robot interaction in the scenarios.

Effects of Over-Loading on Pressure Vessel Integrity

The effect of proof over-pressure on pressure vessels structural integrity is analysed. Risk based approach is applied using Failure Analysis Diagramme to assess likelihood of failure. Special attention is paid to crack-like defects detected by NDT regular testing which are unacceptable by standards, but difficult to be repaired. It was show, using two examples, that such defects can remain if some strict conditions are fulfilled. In any case, with or without crack-like defects, it was shown that testing of pressure vessels with significant over-pressure can cause much more problems than it has benefits, because it acts more like the first step in eventual failure, than being proof to anything.

Effects of pre-existing damage and cyclic overloading on the flexural behaviour of RC beams strengthened with prestressed CFRP plates

Using prestressed carbon fibre-reinforced polymer (CFRP) plates to strengthen reinforced concrete (RC) members is of particular interest to maintain the safe operation of existing bridge structures. This work aims to assess the effects of existing damage in RC beams before strengthening and overloading after strengthening on the reliability of this strengthening technique. A series of tests were conducted to simulate load- and corrosion-induced damage in RC beams and to investigate the flexural behaviour and post-fatigue behaviour of damaged RC beams strengthened with prestressed CFRP plates in anchor systems. The experimental results revealed that the coupling action of corrosion- and cyclic overload-induced damage remarkably reduced the flexural stiffness of the strengthened RC beams but did not greatly impact the ultimate load of the strengthened RC beams, indicating the effectiveness of the prestressed strengthening system. After exposure to cyclic overloading, the strengthened RC beams containing load- and steel corrosion-induced damage had an ultimate load retention of more than 80% and had a similar failure mode of concrete crushing. The proposed model agrees well with the experimental results, implying that it could conservatively predict the ultimate load of strengthened RC beams after exposure to a low-cycle overload.

Robustness of Asymmetric Cyber-Physical Power Systems Against Cyber Attacks

In this paper, we propose a realistic model to investigate the cascading failure process in a cyber-physical power system (CPPS) which can be topologically modeled as an interdependent system consisting of a power network and a cyber-network. To evaluate the robustness of CPPS against cyber-attacks, we take into consideration the effects of computer malware spreading, power redistribution and overloading, and the interdependency between the coupled networks, and then adopt the stochastic failure model to calculate the time interval between the initial cyber-attack and a given level of power loss. We conduct a critical node analysis on the power network to identify the important buses whose removals are likely to trigger a serious blackout. Based on the results of the critical node analysis, we propose both deterministic and stochastic coupling strategies for an asymmetric CPPS with two subnetworks with unequal sizes, to improve its robustness against both random and intentional cyber-attacks. The simulation results on CPPSs built on IEEE 118 Bus and 300 Bus power systems indicate that the proposed coupling methods can effectively improve the system robustness against cyber-attacks.

Experimental study of notched steel beams strengthened with a CFRP plate subjected to overloading fatigue and wetting/drying cycles

Previous studies have verified that carbon fiber reinforced polymer (CFRP) external bonding is a promising strengthening technique for steel structures. However, the adhesive bonding can be affected by both overloading fatigue and hygrothermal exposure, and the tendency has not been clearly understood yet. In this study, eight notched steel beams strengthened with a CFRP plate were tested under four-point bending after suffering from overloading fatigue and/or 400 wetting/drying cycles (WDCs) with 3.5 wt% NaCl solution. The effects of overloading and WDCs on the strength, stiffness, strain distribution and failure modes are discussed. The experimental results show that overloading fatigue and/or WDCs significantly affect the mechanical properties of retrofitted steel beams. The strength and stiffness of the overloaded damaged beams were continuously degraded by WDCs, whereas the beams without overloading damage only suffered from the first 90 WDCs. As observed from the strain distribution and debonding failure modes, the WDCs initiated debonding along the steel beam/adhesive interface and degraded the adhesive bonding over all the bonding surfaces. Meanwhile, overloading damage mainly occurred near the notch and resulted in bond degradation of the CFRP plate/adhesive interface, which induced salt solution penetration and thus further degraded the adhesive bonding.

Effects of Increased Pharyngeal Tissue Mass Due to Fluid Accumulation in the Neck on the Acoustic Features of Snoring Sounds in Men.

Snoring sounds are generated by the vibration of pharyngeal tissue due to the upper airway narrowing. While recorded by a microphone placed over the neck, snoring can pass through the pharyngeal tissue surrounding the upper airway. Thus, changes in the pharyngeal tissue content may change the acoustic properties of the snoring sounds. Rostral fluid shift and the consequent increases in neck fluid volume (NFV) and neck circumference (NC) can increase pharyngeal tissue mass. Therefore, the goal of this study was to investigate the relationship between increases in pharyngeal tissue mass, as assessed by increased NFV and NC, and snoring sounds features. We obtained data from a previous study where 20 males who were not obese participated in a daytime polysomnography and their NC and NFV were measured before and after sleep. During sleep, snoring sounds were recorded with a microphone placed over the neck. Spectral centroid of the snoring sounds was estimated. Then, the first five snoring segments were selected from the first and last 30 minutes of stage N2 sleep. We found a significant decrease in the snoring spectral centroid from the beginning to end of sleep. We also found that spectral centroid from the end of sleep in frequency ranges below 200 Hz was inversely correlated with the increases in NFV and NC from before to after sleep. These results suggest that snoring spectral centroid can be used as a noninvasive and convenient method to assess variations in the pharyngeal tissue mass.

The time response of anaerobic digestion microbiome during an organic loading rate shock.

Knowledge of connections between operational conditions, process stability, and microbial community dynamics is essential to enhance anaerobic digestion (AD) process efficiency and management. In this study, the detailed temporal effects of a sudden glycerol-based organic overloading on the AD microbial community and process imbalance were investigated in two replicate anaerobic digesters by a time-intensive sampling scheme. The microbial community time response to the overloading event was shorter than the shifts of reactor performance parameters. An increase in bacterial community dynamics and in the abundances of several microbial taxa, mainly within the Firmicutes, Tenericutes, and Chloroflexi phyla and Methanoculleus genera, could be detected prior to any shift on the reactor operational parameters. Reactor acidification already started within the first 24h of the shock and headed the AD process to total inhibition in 72h alongside with the largest shifts on microbiome, mostly the increase of Anaerosinus sp. and hydrogenotrophic methanogenic Archaea. In sum, this work proved that AD microbial community reacts very quickly to an organic overloading and some shifts occur prior to alterations on the performance parameters. The latter is very interesting as it can be used to improve AD process management protocols.

Evaporative membrane modulation for comprehensive two-dimensional liquid chromatography

An evaporative membrane modulator was developed, built and evaluated to avoid loss of performance in the second dimension when coupling two-dimensional liquid chromatography systems. The automated interface reduces the volume after 1D elution on-line by a pre-determined factor, regardless of the separation gradient. This volume reduction ensures that the injection volume in the 2D is appropriate for the second column, avoiding the detrimental effects of overloading. In addition, the fraction solvent composition is constant over the length of the separation increasing reproducibility of 2D separations. The evaporative membrane modulator was demonstrated with a 10-fold reduction, reducing the injection volume from 50 to 5 μL. A consequence of the EMM device is a reduction in the capacity of the first dimension, which is decreased by a factor of 2.4, but the peak width at half maximum was reduced by up to 22% in the second dimension. When band broadening is considered, the corrected peak capacity with the modulator was only 10% lower than that without the modulator, but with a gain in peak height of 2–3, and a decrease in retention time between subsequent peak-slices reduced from 4s to be negligible. This improves peak shape and shows potential to facilitate peak identification and quantification in more complex applications.

Effects of Cyber Coupling on Cascading Failures in Power Systems

In this paper, we propose a model to investigate the cascading failures in the coupled system (smart grid) that comprises a power grid and a coupling cyber network. In this model, we take into consideration the effects of power overloading, contagion, and interdependence between power grids and cyber networks on failure propagations in the coupled system, and then use a stochastic method to generate the time intervals between failures, thus producing the dynamic profile of the cascading failures caused by the attack of cyber malwares. We study several coupled systems generated by coupling the UIUC 150 Bus System with cyber networks of different structures and coupling patterns. Simulation results show that the dynamic profile of the cascading failures in a coupled system displays a “staircaselike” pattern which can be interpreted as a combined feature of the typical step propagation profile triggered repeatedly by cyber attacks due to network coupling. Results also show that cyber coupling can intensify both the extent and rapidity of power blackouts. Moreover, the cyber network structure and the coupling patterns affect the propagation of the cascading failures in smart grids. Scale-free cyber networks promote failure spreading, and the higher average cyber node degree also intensifies the spreading. Coupling power nodes with high-degree cyber nodes accelerates the failure propagation compared with random or low-degree couplings.

Measuring Crack Movement in Reinforced Concrete Using Digital Image Correlation: Overview and Application to Shear Slip Measurements

Reinforced concrete infrastructure assets built during the last century are required to stay in-service beyond their intended design lives, which requires techniques that allow the effects of deterioration and overloading to be monitored to ensure these assets are still fit for purpose. One such indicator of distress in a reinforced concrete structure is crack movement; models have been proposed that allow the internal stresses within a structure to be estimated if crack width and slip can be measured. This paper introduces a technique that uses digital image correlation (DIC) to measure not only crack width but also crack slip. The effect of curvature on this measurement technique is discussed and a method for minimizing the errors due to curvature is presented. The technique is used to measure crack width and slip in reinforced concrete beams with both small crack slip and significant crack slip. The results suggest that the technique can be used to measure crack movement in beams once the effects of curvature are accounted for. Future research in this area will focus on development of this technique for use in the field.

NF-κB Signaling Pathway in Controlling Intervertebral Disk Cell Response to Inflammatory and Mechanical Stressors.

Intervertebral disk degeneration (IDD) has a greater than 90% lifetime incidence and is one of the leading causes of chronic back pain in the United States. Despite the high societal cost of IDD, there is limited understanding of the biological effects of mechanical overloading on further degeneration. The transcription factor NF-κB (nuclear factor κB) has been implicated as a key mediator of disk cell response to inflammatory and mechanical stresses and represents a potential control point. The study objective was to measure the effect of NF-κB signaling pathway inhibition on annulus fibrosus (AF) cell matrix synthesis and gene expression under conditions of combined inflammatory and mechanical stimulation. Annulus fibrosus cells were harvested from rabbit intervertebral disks and grown in vitro on flexible plates. The cells were exposed to inflammatory and mechanical stimulation for 24 hours with and without NF-κB inhibition. Nuclear translocation of NF-κB was measured via immunofluorescent staining. Intervertebral disk cell homeostasis was assessed via inflammatory, anabolic, and catabolic gene expression and via matrix synthetic ability. NF-κB nuclear translocation in response to interleukin-1 beta (IL-1β) was reversed with exposure to NF-κB inhibition. NF-κB inhibition decreased matrix metalloproteinase-3, inducible nitric oxide synthase, and cyclooxygenase-2 gene expression and prostaglandin E2 production response to combined inflammatory and mechanical stimulation. Proteoglycan and collagen synthesis were decreased by combined stimulation, but this effect was not reversed by NF-κB inhibition. In vitro modeling of conditions within the disk may not fully reflect the response that AF cells have in native matrix. NF-κB signaling mediates catabolic and inflammatory responses to inflammatory and mechanical stimulation but does not mediate the decrease in matrix synthesis under combined harmful stimulation. Identification of key control points in the cellular responses to inflammatory and mechanical stimuli will facilitate rational design of exercise-based therapies and facilitate synergistic treatments of novel biochemical treatments with rehabilitation regimens.

Peri-implant bone adaptations to overloading in rat tibiae: experimental investigations and numerical predictions.

(i) To assess the effects of mechanical overloading on implant integration in rat tibiae, and (ii) to numerically predict peri-implant bone adaptation. Transcutaneous titanium implants were simultaneously placed into both tibiae of rats (n=40). After 2weeks of integration, the implants of the right tibiae were stimulated daily for 4weeks with loads up to 5N (corresponding to peak equivalent strains of 3300±500με). The effects of stimulation were assessed by exvivo mechanical tests and quantification of bone mineral density (BMD) in selected regions of interests (ROIs). Specimen-specific finite element models were generated and processed through an iterative algorithm to mimic bone adaptation. Bilateral implantation provoked an unstable integration that worsened when mild (2-4N) external loads were applied. In contrast, a stimulation at 5N tended to "counterbalance" the harmful effects of daily activity and, if applied to well-integrated specimens, significantly augmented the implants' resistance to failure (force: +73% P<0.01, displacement: +50% P<0.01 and energy: +153% P<0.01). Specimen-specific numerical predictions were in close agreement with the experimental findings. Both local and overall BMD variations, as well as the implants' lateral stability, were predicted with small errors (0.14gHA/cm3 and 0.64%, respectively). The rats' daily activity detrimentally affects implant integration. Conversely, external stimulations of large magnitudes counterbalance this effect and definitively improve integration. These changes can be predicted using the proposed numerical approach.

Effects of Functional Limb Overloading on Symmetrical Weight Bearing, Walking Speed, Perceived Mobility, and Community Participation among Patients with Chronic Stroke.

Background. Stroke is a leading cause for long-term disability that often compromises the sensorimotor and gait function accompanied by spasticity. Gait abnormalities persist through the chronic stages of the condition and only a small percentage of these persons are able to walk functionally in the community. Material and Method. Patients with chronic stroke were recruited from outpatient rehabilitation unit at Department of Neurology & Neurosurgery, All India Institute of Medical Sciences, having a history of first stroke at least six months before recruitment, with unilateral motor deficits affecting gait. The patients were randomly assigned to either the functional limb overloading (FLO) or Limb Overloading Resistance Training (LORT) group and provided four weeks of training. Result. We found that there was an improvement in gait performance, weight bearing on affected limb, and perceived mobility and community participation. Conclusion. To the best of our knowledge, this is the first study that has evaluated the effects of functional limb overloading training on symmetric weight bearing, walking ability, and perceived mobility and participation in chronic hemiplegic population. The study demonstrated a beneficial effect of training on all the outcomes, suggesting that the functional limb overloading training can be a useful tool in the management of gait problems in chronic stroke patients.

Dietary Phosphorus Overload Aggravates the Phenotype of the Dystrophin-Deficient mdx Mouse

Duchenne muscular dystrophy is a lethal X-linked disease with no effective treatment. Progressive muscle degeneration, increased macrophage infiltration, and ectopic calcification are characteristic features of the mdx mouse, a murine model of Duchenne muscular dystrophy. Because dietary phosphorus/phosphate consumption is increasing and adverse effects of phosphate overloading have been reported in several disease conditions, we examined the effects of dietary phosphorus intake in mdx mice phenotypes. On weaning, control and mdx mice were fed diets containing 0.7, 1.0, or 2.0 g phosphorus per 100 g until they were 90 days old. Dystrophic phenotypes were evaluated in cryosections of quadriceps and tibialis anterior muscles, and maximal forces and voluntary activity were measured. Ectopic calcification was analyzed by electron microscopy to determine the cells initially responsible for calcium deposition in skeletal muscle. Dietary phosphorus overload dramatically exacerbated the dystrophic phenotypes of mdx mice by increasing inflammation associated with infiltration of M1 macrophages. In contrast, minimal muscle necrosis and inflammation were observed in exercised mdx mice fed a low-phosphorus diet, suggesting potential beneficial therapeutic effects of lowering dietary phosphorus intake on disease progression. To our knowledge, this is the first report showing that dietary phosphorus intake directly affects muscle pathological characteristics of mdx mice. Dietary phosphorus overloading promoted dystrophic disease progression in mdx mice, whereas restricting dietary phosphorus intake improved muscle pathological characteristics and function.

Suppressive effects of iron overloading on vascular calcification in uremic rats

BackgroundMedial vascular calcification is a specific complication in chronic kidney disease (CKD) patients although its pathogenesis is poorly understood. The administration of iron (Fe), generally used for the treatment of anemia in CKD patients, induces oxidative stress. Fe loading possibly affects the progress of vascular calcification in uremia. We investigated the effect of Fe on vascular calcification and its mechanism in uremic rats.MethodThirty-two rats were divided into four groups: untreated rats (controls), rats fed a standard diet with Fe administration (Fe group), rats fed an adenine-enriched diet (uremic group), and rats fed an adenine-enriched diet with Fe administration (uremic + Fe group). Iron dextran was administered once a week for 5 weeks intraperitoneally. Morphological alterations and vascular calcification-associated factors in the aortic wall were evaluated.ResultsNo aortic calcification was observed in the control group although uremic rats developed severe vascular calcification. Fe loading suppressed vascular calcification in the uremic groups. Expressions of runt-related transcription factor 2 (Runx2), single-strand (ss)DNA and phosphate transporter (Pit)-1 were increased in the uremic rats compared to the control rats. In the uremic group, Fe administration did not show any effect on ssDNA expression, but reduced Runx2 and Pit-1 expressions.ConclusionFe suppressed the development of vascular calcification through the prevention of Pit-1 and vascular smooth muscle cell osteoblastic transdifferentiation.

Effects of mixed-mode overloading on the mixed-mode I+II fatigue crack growth

In this study, the finite element modeling of the compact tension shear specimens has been used to evaluate the effects of overloading on fatigue crack growth with mixed-mode loading I+II. Element creation and modeling is done by CASCA software. FRANC2D was used for stress analysis and the determination of crack parameters. Life estimation of samples was done by using the software ETBX. To create the mixed-mode I+II, different loading angles of 0, 15, 45 and 75 degrees (with respect to normal direction to the crack surface) were used with various overloading ratios. The effects of residual stresses due to overloading with saving and restoring capabilities were considered as a separate loading. To confirm the modeling results, models were built with ABAQUS and also compared with the results of numerical and experimental data in the literature. There are good agreements in determining the path of the crack growth and life estimation. The effects of the loading direction, overloading ratio and its load ratio, combination of overloadings and their locations on the fatigue crack growth and life are investigated.

Effects of overloading in mastication on the mechanical behaviour of dental implants

Dental implants have become a significant aspect of tooth replacement in prosthodontic treatment. Despite of high success rates, complications and failures still occur. The long-term success of an implant depends on the stability of bone support for the implant. The relationship between occlusal overload and peri-implant bone loss remains a controversial topic in implant dentistry. A causal relationship between the incidence of marginal bone loss next to an implant and occlusal overload implies a treatment plan and occlusal scheme would benefit from a force management approach. The aim of this article is to compare the mechanical behaviour of a dental prosthesis under two loading types (dynamic and dynamic within overload), employing a three dimensional finite element analysis, in order to attempt to clarify causality of overload as related to implant failure and bone loss.

Effects of Mechanical Over-Loading on the Properties of Soleus Muscle Fibers, with or without Damage, in Wild Type and Mdx Mice

Effects of mechanical over-loading on the characteristics of regenerating or normal soleus muscle fibers were studied in dystrophin-deficient (mdx) and wild type (WT) mice. Damage was also induced in WT mice by injection of cardiotoxin (CTX) into soleus muscle. Over-loading was applied for 14 days to the left soleus muscle in mdx and intact and CTX-injected WT mouse muscles by ablation of the distal tendons of plantaris and gastrocnemius muscles. All of the myonuclei in normal muscle of WT mice were distributed at the peripheral region. But, central myonuclei were noted in all fibers of WT mice regenerating from CTX-injection-related injury. Further, many fibers of mdx mice possessed central myonuclei and the distribution of such fibers was increased in response to over-loading, suggesting a shift of myonuclei from peripheral to central region. Approximately 1.4% branched fibers were seen in the intact muscle of mdx mice, although these fibers were not detected in WT mice. The percentage of these fibers in mdx, not in WT, mice was increased by over-loading (∼51.2%). The fiber CSA in normal WT mice was increased by over-loading (p<0.05), but not in mdx and CTX-injected WT mice. It was suggested that compensatory hypertrophy is induced in normal muscle fibers of WT mice following functional over-loading. But, it was also indicated that muscle fibers in mdx mice are susceptible to mechanical over-loading and fiber splitting and shift of myonuclei from peripheral to central region are induced.