A mixed-mode fracture specimen: analysis and testing

A mixed-mode fracture specimen which is employed to measure K _I and K _II failure values for 0K _I /K _II 0.28 is analyzed. In order to perform experiments, specimen calibration formulas relating K _I and K _II to the applied load and specimen geometric parameters must be obtained.To this end, a mixed-mode weight function method is applied to the specimen, requiring the stress intensity factors and displacement fields induced by two different loading cases. These quantities are determined by means of a finite element analysis which makes use of a singular crack tip element. For this range of K ratio, the stress field in the central region of the specimen before crack introduction is nearly uniform; hence, expressions for the desired mixed-mode stress intensity factors may be written as the product of two factors; one depending upon crack length and one depending upon loading angle.Once the K calibration formulas are obtained as a function of applied load and specimen geometry, testing may be carried out. Here, perspex specimens are tested; results for K _I , K _II and crack propagation angle at fracture compare reasonably well with failure curves determined from an extended maximum tangential stress criterion.

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Résumé On analyse le cas d'une éprouvette présentant une rupture de mode mixte en vue de mesurer les valeurs à la rupture de K _I et K _II , le rapport K ₁ /K ₂ étant compris entre 0 et 0,28. Pour réaliser l'expérience, il y a lieu d'établir les formules d'étalonnage mettant en relation K _I et K _II avec la charge appliquée et les paramètres géométriques de l'éprouvette.A cette fin, on applique à l'éprouvette une méthode de fonction pondérée de mode mixte, requérant les valeurs des facteurs d'intensité de contraintes et les champs de déplacement induits par deux cas de mise en charge différents.Ces quantités sont déterminées grâce à une analyse par éléments finis utilisant un élément singulier à l'extrémité de la fissure.Pour les rapports de K ci-dessus, le champ de contraintes dans la région centrale de l'éprouvette avant introduction de la fissure est sensiblement uniforme. On peut, dès lors, écrire les expressions des facteurs d'intensité de contrainte correspondant au mode mixte désiré sous forme d'une produit de deux facteurs: l'un dépend de la longueur de fissure et l'autre de l'angle de mise en charge.L'essai peut être exécuté une fois obtenues les formules d'étalonnage de K en fonction de la charge appliquée et de la géométrie de l'éprouvette. On utilise dans le cas présent des éprouvettes en perspex, et les résultats pour K _I , K _II et l'angle de propagation de la fissure lors de la rupture concordent assez bien avec les courbes de rupture déterminée à partir d'une critère élargi de la tension tangentielle maximale.

     

Ubiquitin Ligases in Longevity and Aging Skeletal Muscle

The development and prevalence of diseases associated with aging presents a global health burden on society. One hallmark of aging is the loss of proteostasis which is caused in part by alterations to the ubiquitin–proteasome system (UPS) and lysosome–autophagy system leading to impaired function and maintenance of mass in tissues such as skeletal muscle. In the instance of skeletal muscle, the impairment of function occurs early in the aging process and is dependent on proteostatic mechanisms. The UPS plays a pivotal role in degradation of misfolded and aggregated proteins. For the purpose of this review, we will discuss the role of the UPS system in the context of age-related loss of muscle mass and function. We highlight the significant role that E3 ubiquitin ligases play in the turnover of key components (e.g., mitochondria and neuromuscular junction) essential to skeletal muscle function and the influence of aging. In addition, we will briefly discuss the contribution of the UPS system to lifespan. By understanding the UPS system as part of the proteostasis network in age-related diseases and disorders such as sarcopenia, new discoveries can be made and new interventions can be developed which will preserve muscle function and maintain quality of life with advancing age.     

Coming to Terms with End-User Systems Integration

Despite the phenomenal growth of end-user computing, managers and planners have lit-tie to guide them when developing integrated systems for the future of their organizations. This article tackles the problem of systems integration at its roots in organizational theory and formulates a practical framework for end-user planning.     

Mars Helicopter Exceeds Expectations

On 19 April 2021,its twin rotors stirring the wispy Martian atmosphere,Ingenuity,the National Aeronautics and Space Administration(NASA)miniature helicopter,lif...     

Distribution of Quasimidranges and Associated Mixtures

In this paper are presented and discussed tabulations of the cumulative distribution functions of quasimidranges and mixtures of quasimidranges of samples from a normal distribution. The tabulations extend up to samples of size 21. For quasimidranges not involving the extreme values of the sample, the departure from normality is very small. The physical problem giving rise to the mixtures is discussed.     

Analysis of in situ monitored thermal cycling benefits for wireless packaging early reliability evaluation

With the increasing complexity of the power amplifier (PA) module architecture, the probability of a thermally induced stress related failure mechanism increases. To help evaluate the increase in module complexity, a more sophisticated in situ monitored thermal cycle reliability test is available. The module is monitored in real time using a resistance daisy chain methodology designed to provide coverage using resistance feedback throughout the entire hierarchy of the module and carrier board interface. Monitored temperature cycling allows for real time failure feedback and enhanced failure signature information. Further, the testing technique has proven to be a valuable method for capturing the early stages of a module mechanical failure at the temperature extremes. Moreover, statistical evaluation of the failure data (Weibull analysis) is improved and better accuracy of the failures in time (FIT) rate can be determined.     

Evaluation of a Brix refractometer to estimate serum immunoglobulin G concentration in neonatal dairy calves

The objective of this study was to evaluate the utility of a digital Brix refractometer for the assessment of success of passive transfer of maternal immunoglobulin compared with the measurement of serum total protein (STP) by refractometry. Blood samples (n = 400) were collected from calves at 3 to 6d of age. Serum IgG concentration was determined by radial immunodiffusion (RID), and STP and percentage Brix (%Brix) were determined using a digital refractometer. The mean IgG concentration was 24.1 g/L [standard deviation (SD) ± 10.0] with a range from 2.1 to 59.1 g/L. The mean STP concentration was 6.0 g/dL (SD ± 0.8) with a range from 4.4 to 8.8 g/dL. The mean %Brix concentration was 9.2% (SD ± 0.9) with a range of 7.3 to 12.4%. Brix percentage was highly correlated with IgG (r = 0.93). Test characteristics were calculated to assess failure of passive transfer (FPT; serum IgG <10 g/L). The sensitivity and specificity of STP at 5.5 g/dL were 76.3 and 94.4%, respectively. A receiver operating characteristic curve was created to plot the true positive rate against the false positive rate for consecutive %Brix values. The optimal combination of sensitivity (88.9%) and specificity (88.9%) was at 8.4% Brix. Serum total protein was also positively correlated with %Brix (r = 1.00) and IgG (r = 0.93). Dairy producers can successfully monitor their colostrum management and the overall success of passive transfer using a digital Brix refractometer to estimate IgG concentration of colostrum and calf serum.