Treatment of singularities in cracked bodies

Three-dimensional finite-element analyses of middle-crack tension (M-T) and bend specimens subjected to mode I loadings were performed to study the stress singularity along the crack front. The specimen was modeled using 20-node isoparametric elements. The displacements and stresses from the analysis were used to estimate the power of singularities using a log-log regression analysis along the crack front. The analyses showed that finite-sized cracked bodies have two singular stress fields of the form rho = C sub o (theta, z) r to the -1/2 power + D sub o (theta, phi) R to the lambda rho power. The first term is the cylindrical singularity with the power -1/2 and is dominant over the middle 96 pct (for Poisson's ratio = 0.3) of the crack front and becomes nearly zero at the free surface. The second singularity is a vertex singularity with the vertex point located at the intersection of the crack front and the free surface. The second term is dominant at the free surface and becomes nearly zero away from the the boundary layer. The thickness of the boundary layer depends on Poisson's ratio of the material and is independent of the specimen type. The thickness of the boundary layer varied from 0 pct to about 5 pct of the total specimen thickness as Poisson's ratio varied from 0.0 to 0.45. Because there are two singular stress fields near the free surface, the strain energy release rate (G) is an appropriate parameter to measure the severity of the crack

Implementation of equivalent domain integral method in the two-dimensional analysis of mixed mode problems

An equivalent domain integral (EDI) method for calculating J-intergrals for two-dimensional cracked elastic bodies is presented. The details of the method and its implementation are presented for isoparametric elements. The total and product integrals consist of the sum of an area of domain integral and line integrals on the crack faces. The line integrals vanish only when the crack faces are traction free and the loading is either pure mode 1 or pure mode 2 or a combination of both with only the square-root singular term in the stress field. The EDI method gave accurate values of the J-integrals for two mode I and two mixed mode problems. Numerical studies showed that domains consisting of one layer of elements are sufficient to obtain accurate J-integral values. Two procedures for separating the individual modes from the domain integrals are presented. The procedure that uses the symmetric and antisymmetric components of the stress and displacement fields to calculate the individual modes gave accurate values of the integrals for all problems analyzed. The EDI method when applied to a problem of an interface crack in two different materials showed that the mode 1 and mode 2 components are domain dependent while the total integral is not. This behavior is caused by the presence of the oscillatory part of the singularity in bimaterial crack problems. The EDI method, thus, shows behavior similar to the virtual crack closure method for bimaterial problems

Secure and Efficient DiDrip Protocol for Improving Performance of WSNs

Wireless Sensor Networks consists of a set of resource constrained devices called nodes that communicate wirelessly with each other. Wireless Sensor Networks have become a key application in number of technologies. It also measures the unit of vulnerability to security threats. Several Protocols are projected to make them secure. Some of the protocols within the sensor network specialize in securing data. These protocols are named as data discovery and dissemination protocols. The data discovery and dissemination protocol for wireless sensor networks are utilized for distributing management commands and altering configuration parameters to the sensor nodes. All existing data discovery and dissemination protocols primarily suffer from two drawbacks. Basically, they are support centralized approach (only single station can distribute data item).This approach is not suitable for multiple owner-multiple users. Second, the protocols are not designed with security in mind. This Paper proposes the first distributed knowledge discovery and dissemination protocol called DiDrip which is safer than the existing one. The protocol permits multiple owners to authorize many network users with altogether totally different priorities to at an equivalent time and directly flow into data items to sensor nodes

DiDrip: A Secure and Distributed Protocol for Updation and Dissemination of Data in WSN

A data discovery and dissemination protocol for wireless sensor networks (WSNs) is responsible for updation of configuration parameters and distribution of management commands to the sensor nodes. The existing data discovery and dissemination protocols faces several drawbacks. The idea behind the project is to use the first secure and distributed data discovery and dissemination protocol named DiDrip for WSN. DiDrip allows the network owners to authorize multiple network users with different privileges to directly and simultaneously disseminate data items to the nodes. Extensive security analysis shows that DiDrip is probably secure

Distinguishing Motor Weakness From Impaired Spatial Awareness: A Helping Hand!

Our patient, aged 73 years, had background peripheral neuropathy of unknown cause, stable for several years, which caused some difficulty in walking on uneven ground. He attended for a teaching session but now staggered in, a new development. He had apparent weakness of his right arm, but there was difficulty in distinguishing motor weakness from impaired spatial awareness suggestive of parietal lobe dysfunction. With the patient seated, eyes closed, and left arm outstretched, S.A.R. lifted the patient’s right arm and asked him to indicate when both were level. This confirmed motor weakness. Urgent computed tomographic scan confirmed left subdural haematoma and its urgent evacuation rapidly resolved the patient’s symptoms. Intrigued by our patient’s case, we explored further and learnt that in rehabilitation medicine, the awareness of limb position is commonly viewed in terms of joint position sense. We present recent literature evidence indicating that the underlying mechanisms are more subtle