Fatigue and collapse of cyclically bent strip of amorphous solid

Fatigue caused by cyclic bending of a piece of material, resulting in its mechanical failure, is a phenomenon that had been studied for ages by engineers and physicists alike. In this Letter we study such fatigue in a strip of athermal amorphous solid. On the basis of atomistic simulations we conclude that the crucial quantity to focus on is the accumulated damage. Al- though this quantity exhibits large sample-to-sample fluctuations, its dependence on the loading determines the statistics of the number of cycles to failure. Thus we can provide a scaling theory for the Wo ̈hler plots of mean number of cycles for failure as a function of the loading amplitude.

Association between Cognitive Impairment and Olfactory Deficits in Systemic Lupus Erythematosus Without Major Neuropsychiatric Syndromes

Objective Cognitive impairment is a common neuropsychiatric manifestation of systemic lupus erythematosus (SLE). However, it is not routinely assessed despite its high morbidity and mortality. The aim of the study was to investigate the utility of a brief neuropsychological battery, the Repeatable Battery for the Assessment of Neuropsychological Status (RBANS), to evaluate cognitive deficits in patients with SLE and to examine the relationship between cognitive and olfactory function. Methods Fifty-five SLE patients and 50 age- and sex-matched healthy control subjects were administered the Repeatable Battery for the Assessment of Neuropsychological Status (RBANS), a cognitive screening battery that evaluated five index of cognition including immediate memory (IMME), visuospatial/constructional (Vis/Con), language (LANG), attention (ATT), delayed memory (DEME). Olfactory functions were evaluated using olfactory function assessment by computerized testing including the three stages of smell: threshold (THR), identification (ID) and memory (ME) of the different odors. The disease activity and cumulative damage were assessed by the SLE Disease Activity Index 2000 (SLEDAI-2K) and the Systemic Lupus International Collaborating Clinics (SLICC)/American College of Rheumatology(ACR) Damage Index (SDI). Results Patients with SLE exhibited significant lower total RBANS score, IMME, Vis/Con, ATT and DEME index scores than normal controls (P < 0.01 for all and P = 0.027 for attention). Performances on RBANS immediate memory, language, attention and total scores were correlated with education level of SLE patients. Reduced RBANS index and total scores were associated with several organ involvement and autoantibodies. SLE patients with higher SLEDAI-2K scores or with accumulated damage (SDI≥1) showed decreased RBANS scores than patients with lower SLEDAI-2K scores or without accumulated damage. All the olfactory scores (THR, ID and ME) in patients with SLE were significantly decreased than the control group (all P = 0.001). Patients had higher proportion of anosmia (8.57% vs 0%) and hyposmia (28.58% vs 5.72%) than controls (χ2 = 10.533, P = 0.015). Multivariable regression analysis revealed that olfactory threshold, identification and memory had a positive effect on RBANS index score. Olfactory memory and total score were significantly correlated with the RBANS delayed memory (r = 0.393, P = 0.021) and total scores (r = 0.429, P = 0.011).Conclusion The results of this study indicate that significantly correlated cognitive and olfactory functions are impaired in SLE patients. The RBANS is a potentially useful instrument for evaluating neuropsychological status in SLE. Physicians are encouraged to perform routine screening in patients with SLE to detect subtle cognitive dysfunction and strategize early treatment options.

Damage mode identification of Carbon fiber/Epoxy composites under fatigue process using acoustic emission monitoring

In this paper, the static and fatigue behavior of carbon fiber/Epoxy composites laminate are investigated. The degradation and damage evolution in the composite laminate tests process were monitored using the acoustic emission technique. The acoustic signals collected during the tests were analyzed. The results of the acoustic emission signal accumulated during static and fatigue tests are compared in order to identify the accumulated damage mechanism of carbon fiber/Epoxy composites laminate. The accumulated damage is manifested by matrix cracking, fiber/matrix interface debonding, shear failure, delamination, and fiber break.

SENSIBILIDADE DE PARÂMETROS DA ESTRUTURA NA ANÁLISE DE DESEMPENHO DE PAVIMENTOS FLEXÍVEIS

The design of asphalt pavement structures is a process that involves the knowledge of variables that are difficult to predict and model.Sensitivity analysis applied to pavement performance prediction is essential to determine the most influential variables, and enable the optimization of design process. This study aimed to analyze the sensitivity of flexible pavements performance to variations in design parameters related to the thicknesses of asphalt layer, base and sub-base and resilient modulus of asphalt layer, base, sub-base and subgrade. For this purpose, a fractional factorial experiment was conducted, which had as output variables the accumulated damage in pavement structure, related to fatigue cracking and rutting in wheel wander. To obtain the accumulated damage, mechanistic-empirical design method was used, through PerRoad software. It was concluded that asphalt layer thickness isthe most sensitive parameter considering the distresses studied, having a higher sensitivity for fatigue cracking and a slightly lower sensitivity for rutting.

Imbalance Detection of Rotor Rotational Speed Using Doppler Radar

In operating a wind turbine, both predictive and condition-based maintenances are required to minimize the downtime caused by maintenance. The imbalance of rotor rotational speed is an important factor for diagnosing wind turbine failures. The rotational speed imbalance can be caused by accumulated damage or the accumulation of ice, dust, and moisture. In this paper, we proposed a method for detecting the rotational speed imbalance of a wind turbine using a Doppler radar. We calculated the difference in the rotational speed for different times using spectrograms obtained by observing the wind turbine with a Doppler radar and determined the rotational speed imbalance using the fast Fourier transform. The performance of the proposed algorithm was verified using both synthetic and numerical data.

The Consequences of Budding versus Binary Fission on Adaptation and Aging in Primitive Multicellularity

Early multicellular organisms must gain adaptations to outcompete their unicellular ancestors, as well as other multicellular lineages. The tempo and mode of multicellular adaptation is influenced by many factors including the traits of individual cells. We consider how a fundamental aspect of cells, whether they reproduce via binary fission or budding, can affect the rate of adaptation in primitive multicellularity. We use mathematical models to study the spread of beneficial, growth rate mutations in unicellular populations and populations of multicellular filaments reproducing via binary fission or budding. Comparing populations once they reach carrying capacity, we find that the spread of mutations in multicellular budding populations is qualitatively distinct from the other populations and in general slower. Since budding and binary fission distribute age-accumulated damage differently, we consider the effects of cellular senescence. When growth rate decreases with cell age, we find that beneficial mutations can spread significantly faster in a multicellular budding population than its corresponding unicellular population or a population reproducing via binary fission. Our results demonstrate that basic aspects of the cell cycle can give rise to different rates of adaptation in multicellular organisms.

Stiffness Degradation of Digital Polypropylene Under Fatigue Loading: Investigations via 3-Dimensional Polyjet Printed Coupons

The utilization of additively manufactured parts is gaining popularity in functional applications. Polymer-based additive manufacturing (AM) parts are utilized in a variety of engineering applications for automotive, aerospace, and energy. AM printed parts are however newer class of materials, and structural performance of these materials is not fully understood completely, and very limited exists currently on precisely performance of Polyjet printed parts and associated digital materials under fatigue loading. This paper investigates the stiffness degradation under tension-tension fatigue loading of digital polypropylene using homogenous 3-Dimensional test coupons formed using PolyJet printing. Homogeneous 3-Dimensional test configuration employed in the present study eliminates the process-induced limitations of traditional ASTM D638 2D fatigue test coupons for AM processed materials. Fatigue data is analyzed to present an empirical model of effective elastic modulus and an analytical model of the accumulated damage state, as defined on the basis of stiffness degradation during cyclic loading. Further, the actual damage accumulation due to cyclic loading with the predicted model is compared. Modeling of the S-N diagram provides a better estimation of fatigue life and fatigue life modeling of AM printed test coupons and is obtained via linear regression analysis of experimental data with high correlation coefficient R2 (0.9971). The analytical model of the accumulated damage state is based on the stiffness degradation and is derived from the regression analysis of experimental data of stiffness degradation at different loading percentages assuming a polynomial of degree 4. Present study provides insight into the fatigue damage state and cyclic performance of digital polypropylene from Polyjet printing.