: An overview of the virtual crack closure technique is presented. The approach used is discussed, the history summarized, and insight into its applications provided. Equations for two-dimensional quadrilateral elements with linear and quadratic shape functions are given. Formula for applying the technique in conjuction with three-dimensional solid elements as well as plate/shell elements are also provided. Necessary modifications for the use of the method with geometrically nonlinear finite element analysis and corrections required for elements at the crack tip with different lengths and widths are discussed. The problems associated with cracks or delaminations propagating between different materials are mentioned briefly, as well as a strategy to minimize these problems. Due to an increased interest in using a fracture mechanics based approach to assess the damage tolerance of composite structures in the design phase and during certification, the engineering problems selected as examples and given as references focus on the application of the technique to components made of composite materials.

/pdf/virtual-crack-closure-technique-history-approach-and-53akn4ewzt.pdf

Virtual crack closure technique: History, approach, and applications

Fracture toughness of the tensile and compressive fibre failure modes in laminated composites

An intralaminar damage model, based on a continuum damage mechanics approach, is presented to model the damage mechanisms occurring in carbon fibre composite structures incorporating fibre tensile and compressive breakage, matrix tensile and compressive fracture, and shear failure. The damage model, together with interface elements for capturing interlaminar failure, is implemented in a finite element package and used in a detailed finite element model to simulate the response of a stiffened composite panel to low-velocity impact. Contact algorithms and friction between delaminated plies were included, to better simulate the impact event. Analyses were executed on a high performance computer (HPC) cluster to reduce the actual time required for this detailed numerical analysis. Numerical results relating to the various observed interlaminar damage mechanisms, delamination initiation and propagation, as well as the model’s ability to capture post-impact permanent indentation in the panel are discussed. Very good agreement was achieved with experimentally obtained data of energy absorbed and impactor force versus time. The extent of damage predicted around the impact site also corresponded well with the damage detected by non destructive evaluation of the tested panel.

Predicting low-velocity impact damage on a stiffened composite panel

https://digitalcommons.unl.edu/cgi/viewcontent.cgi?article=1083&context=mechengfacpub

Peridynamic model for dynamic fracture in unidirectional fiber-reinforced composites

A status report on delamination resistance testing of polymer-matrix composites

Intralaminar fracture toughness of a cross-ply laminate and its constituent sub-laminates

Background: Diabetes is a major public health problem in India. However, awareness on diabetes is still remaining challenges in Indian population. This study aimed to assess the knowledge about risk factors, symptoms and complications of diabetes and its association with socio demographic factors.

Methods: The study was carried out at Neelambur, south India. A total of 500 adults were randomly selected and interviewed using a pretested specifically designed questionnaire. 

Results: Of 500 participants interviewed, 42.4% perceived high consumption of sugar as an important risk factor for developing diabetes. Only 54.4%, 47.8%, 58.4%, 53.6% and 45.4% perceived presence of family history of diabetes, obesity, increasing age, physical inactivity and stress as risk factors for diabetes. Majority of them felt slow healing of wound as a symptom for diabetes, but feeling of thirst, frequent urination and tiredness as a symptom for diabetes were identified by only 58.6%, 73.8%, and 73.8% respectively. Only 59.6% of participants understood that diabetes could produce complications. A higher education and presence of family history of diabetes were found to be positively associated with more diabetes knowledge.

Conclusion: This study highlights that there is lack of awareness of major risk factors for diabetes. Level of education and presence of family history of diabetes are the most significant factors associated with knowledge regarding risk factors, symptoms and complications of diabetes. Massive diabetes health education programs are urgently needed in this population.

/pdf/knowledge-about-risk-factors-symptoms-and-complications-of-4zrghil5dr.pdf

Knowledge about risk factors, symptoms and complications of diabetes among adults in South India -

Intralaminar fracture toughness values of [0°] 3 0 , [45°] 3 0 and [90°] 3 0 carbon/epoxy laminates are theoretically evaluated based on the well-known MCCI method corresponding to the fracture loads obtained by testing C(T) specimens. Comparison of fracture toughness of angle ply laminate, which is associated with both mode I and mode II, show a very good agreement with the theoretical prediction. A new empirical relationship is developed to obtain the intralaminar fracture toughness of an angle ply laminate from the corresponding value of the 0° laminate. The new formula is used to compare fracture toughness of angle ply laminates available in literature for glass epoxy Scotch ply 1002 laminate and a reasonably good agreement is observed between the test data and the predictions. As a percentage of total fracture toughness value, toughness due to mode II is maximum of 15.5% when fibre orientation is 45°.

http://nopr.niscair.res.in/bitstream/123456789/20180/1/IJEMS%209%284%29%20269-274.pdf

Evaluation of intralaminar fracture toughness of angle ply laminate

https://journals.sagepub.com/doi/pdf/10.1177/096369350000900503

Studies on Mixed Mode Interlaminar Fracture Toughness of M55J/M18 Carbon/Epoxy Laminates

Analytical solution for the tangential stress distribution ahead of a hole is needed for the theoretical prediction of notched strength of brittle laminate using the well-known W-N criteria. In the present study, tangential stress distribution in an orthotropic circular cylindrical shell under uniaxial loading with a circular hole is obtained intuitively with the use of a stress function. A good agreement is obtained for the stresses around and ahead of the circular hole in (0 deg 4 ± 30 deg) s and 90 deg laminates with the finite element results.

S. Jose

Papers

Intralaminar fracture toughness of a cross-ply laminate and its constituent sub-laminates

Knowledge about risk factors, symptoms and complications of diabetes among adults in South India -

Evaluation of intralaminar fracture toughness of angle ply laminate

Studies on Mixed Mode Interlaminar Fracture Toughness of M55J/M18 Carbon/Epoxy Laminates

Analytical Solution for W-N Criteria for the Prediction of Notched Strength of an Orthotropic Shell