Simulation of delamination initiation and subsequent propagation using cohesive zones

2017 ◽  
Author(s):  
Maofen Zhang ◽  
Daoguo Yang ◽  
Leo Ernst ◽  
Bingbing Zhang
Keyword(s):  
Subsequent Propagation ◽  
Cohesive Zones

Delamination resistance of composite laminated structures reinforced with angled, threaded, and anchored Z-pins

2018 ◽  
Vol 53 (11) ◽  
pp. 1507-1519 ◽  
Author(s):  
Ananth Virakthi ◽  
Soonwook Kwon ◽  
Sung W Lee ◽  
Mark E Robeson
Keyword(s):  
Fracture Toughness ◽  
Double Cantilever Beam ◽  
Nonlinear Finite Element ◽  
Mode I ◽  
Finite Element Models ◽  
Mechanical Interlocking ◽  
Delamination Resistance ◽  
Novel Approaches ◽  
Laminated Structures ◽  
Cohesive Zones

The delamination resistance of Z-pinned laminates is directly dependent on the strength of the pin–laminate bonding at the interface. In this paper, we investigate novel approaches to the Z-pinning technology in order to increase delamination strength via enhancing mechanical interlocking of the pins. Toward this end, we study the effect of pin insertion at an angle to the vertical in contrast to the conventional vertical pin insertion. Subsequently, a novel variety of pin, namely the threaded pin, is studied as a candidate for reinforcement which increases mechanical interlocking between the pin and the laminate as well as the epoxy-pin contact area, thus delaying delamination. In addition, the effect of anchoring reveals the length of smooth metal pins on to the surface of the laminate before curing on delamination strength is investigated. Experiments performed show increase in tensile pullout strengths when angled, threaded, or anchored pins are used. These experimental results for tensile pullout strengths validate nonlinear finite element models incorporating cohesive zones at the pin–laminate interface. In addition, fracture toughness and delamination resistance under mode-I loading are investigated by performing experiments on double cantilever beam specimens. Results demonstrate the superior delamination resistance properties for angled, threaded, and anchored pin inserts.

scholarly journals Micromechanical Analyses of Debonding and Matrix Cracking in Dual-Phase Materials

2016 ◽  
Vol 83 (5) ◽  
Author(s):  
Brian Nyvang Legarth ◽  
Qingda Yang
Keyword(s):  
Biaxial Loading ◽  
Matrix Cracking ◽  
Dual Phase ◽  
Load Carrying Capacity ◽  
Matrix Cracks ◽  
Loading Direction ◽  
Load Carrying ◽  
The Matrix ◽  
Cohesive Zones ◽  
Good Agreement

Failure in elastic dual-phase materials under transverse tension is studied numerically. Cohesive zones represent failure along the interface and the augmented finite element method (A-FEM) is used for matrix cracking. Matrix cracks are formed at an angle of 55 deg−60 deg relative to the loading direction, which is in good agreement with experiments. Matrix cracks initiate at the tip of the debond, and for equi-biaxial loading cracks are formed at both tips. For elliptical reinforcement the matrix cracks initiate at the narrow end of the ellipse. The load carrying capacity is highest for ligaments in the loading direction greater than that of the transverse direction.

scholarly journals Propagation of Threatened Nepenthes khasiana: Methods and Precautions

2015 ◽  
Vol 7 (3) ◽  
pp. 313-315
Author(s):  
Jibankumar S. KHURAIJAM ◽  
Rup K. ROY
Keyword(s):  
Plant Species ◽  
Threatened Species ◽  
Ex Situ Conservation ◽  
Ex Situ ◽  
In The Wild ◽  
Propagation Technique ◽  
Subsequent Propagation ◽  
Nepenthes Khasiana

Ex-situ conservation is an important key in the management of rare, endangered and threatened (RET) plant species and its effectiveness depends on several factors. Maintenance of viable germplasm and its subsequent propagation plays an important role in long term conservation of many RET species. Nepenthes khasiana is a rare and gravely threatened species in the wild due to over-collection and other threats. The species needs urgent in-situ and ex-situ conservation. Development of easy to propagate techniques would pave faster multiplication for its use of educational, medicinal and horticultural purpose. In the present paper, successful propagation technique of Nepenthes khasiana through seeds is demonstrated along with detailed information on precautions to be taken during the adoption of the techniques.

Fatigue Life Assessment of Fastened Composite (FRP and CRP) Plates: A Comparative Study

2011 ◽  
Vol 110-116 ◽  
pp. 1155-1160
Author(s):  
K.N. Pandey ◽  
Yogesh K. Tembhurne
Keyword(s):  
Fatigue Life ◽  
Composite Materials ◽  
Composite Laminates ◽  
Maximum Load ◽  
Butt Joint ◽  
Fatigue Tests ◽  
Life Assessment ◽  
Reinforced Plastic ◽  
Mechanically Fastened ◽  
Subsequent Propagation

Composite materials are now a day most frequently used materials in aerospace structures. Mechanically fastened joints are usually used there for joining process due to number of advantages over other conventional joints. These joints are easy to assemble and dissemble and are cheaper. However, they create stress concentration near the hole, leading to source of nucleation and subsequent propagation of cracks under cyclic loading. They also increase weight of the system tat may nullify the advantages we get from composite materials. The present work intent to find fatigue life of two composite laminates usually employed in spacecraft structures. The composites studies are fiberglass reinforced Plastic (FRP) and Carbon Reinforced Plastic (CRP). After preparing the composites, moisture, tension and fatigue tests were conducted on both composites. To know the behavior under damped condition, absorption tests were conducted. Fatigue tests were done both under as plate and butt joint conditions. It was found that in bolted joint condition, both CRP and FRP plates fails in net tension at minimum load but for maximum load they fail in shear.

scholarly journals A review of atmospheric gravity waves and travelling ionospheric disturbances: 1982-1995

1996 ◽  
Vol 14 (9) ◽  
pp. 917-940 ◽  
Author(s):  
K. Hocke ◽  
K. Schlegel
Keyword(s):  
Gravity Waves ◽  
Ionospheric Disturbances ◽  
Atmospheric Gravity Wave ◽  
Atmospheric Gravity Waves ◽  
Travelling Ionospheric Disturbances ◽  
The Past ◽  
Low Latitudes ◽  
Subsequent Propagation ◽  
Atmospheric Gravity ◽  
Inversion Techniques

Abstract. Recent investigations of atmospheric gravity waves (AGW) and travelling ionospheric disturbances (TID) in the Earth\\'s thermosphere and ionosphere are reviewed. In the past decade, the generation of gravity waves at high latitudes and their subsequent propagation to low latitudes have been studied by several global model simulations and coordinated observation campaigns such as the Worldwide Atmospheric Gravity-wave Study (WAGS), the results are presented in the first part of the review. The second part describes the progress towards understanding the AGW/TID characteristics. It points to the AGW/TID relationship which has been recently revealed with the aid of model-data comparisons and by the application of new inversion techniques. We describe the morphology and climatology of gravity waves and their ionospheric manifestations, TIDs, from numerous new observations.

Observations of radio frequency noise from Ariel 4

1975 ◽  
Vol 343 (1633) ◽  
pp. 227-240 ◽  
Keyword(s):  
Radio Frequency ◽  
Electromagnetic Waves ◽  
Space Vehicles ◽  
Frequency Noise ◽  
Simple Theories ◽  
Cusp Region ◽  
Moderate Energy ◽  
Subsequent Propagation ◽  
Ambient Electron ◽  
Upper Ionosphere

Radio frequency observations of noise in the upper ionosphere were made with a 12 m electric dipole and a narrow-band receiver which either swept from 0.25 to 4.0 MHz every 16 s or operated at a fixed frequency of 2 MHz. Several distinct types of noise were observed. One is similar to that previously studied by a number of space vehicles close to the electron gyro- and plasma frequencies. Evidence is presented that simple theories based on the generation of electromagnetic waves by Cerenkov radiation in a cold plasma with subsequent propagation are inadequate to account for this noise. Two other kinds of noise observed may be locally generated; one at least, which has an impulsive character, by an interaction between the satellite and the plasma. As the satellite crosses the auroral regions, an interesting series of apparently related phenomena is observed when comparison is made with data from other experiments on the satellite. This is most clearly defined in the ‘daytime cusp’ region. An enhancement of the radio noise is accompanied by intense bursts of electrons in the moderate energy range at and below 1 keV, typical of this region, and by a sharp dip in the ambient electron density. The latter is presumably the daytime extension of the ionospheric ‘trough’.

A Scanning and Transmission Electron Microscopic Study of Rotavirus-Induced Intestinal Lesions in Neonatal Gnotobiotic Dogs

1986 ◽  
Vol 23 (4) ◽  
pp. 443-453 ◽  
Author(s):  
C. A. Johnson ◽  
T. G. Snider ◽  
W. G. Henk ◽  
R. W. Fulton
Keyword(s):  
Epithelial Cells ◽  
Ultrastructural Changes ◽  
Post Inoculation ◽  
Electron Microscopic ◽  
Intestinal Villi ◽  
Villus Atrophy ◽  
Intestinal Lesions ◽  
Transmission Electron ◽  
Transmission Electron Microscopic ◽  
Subsequent Propagation

Neonatal gnotobiotic dogs orally inoculated with canine rotavirus had ultrastructural changes limited to the jejunal and ileal regions of the small intestine. Early scanning electron microscopic findings consisted of swollen villus epithelial cells, denuded foci on intestinal villi, and slight to moderate villus atrophy. Later changes were slight villus atrophy with no denuded intestinal villi. Transmission electron microscopic changes in villus epithelial cells from 12 to 48 hours post-inoculation included: rotavirus particles associated with intracytoplasmic vacuoles near the terminal web and apical tubules; viral particles in dilated cisternae of rough endoplasmic reticulum; and moderate numbers of necrotic cells having no microvilli, swollen mitochondria, membrane-bound lipid-like material in the cytoplasm, clumped chromatin around the periphery of the nucleus, and disruption of the cytoplasmic membrane. In jejunum and ileum at 72 to 154 hours post-inoculation, there were fewer necrotic villus epithelial cells and fewer virus particles. In addition, the ultrastructural morphology of the majority of the villus epithelial cells was similar to crypt epithelium. These studies showed that rotavirus infected the villus epithelial cells with subsequent propagation of the rotavirus and destruction of villus epithelial cells.

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