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Effects of Voids on Delamination Growth in Composite Laminates under CompressionZhuang, Linqi 14 March 2013 (has links)
Polymer matrix composites are widely used as structural components in the aerospace industry and wind turbine industry etc. to take advantage of their unique mechanical properties and weight saving ability. Although there have been considerable developments in analyzing delamination growth and effects of voids on certain mechanical properties of composites, none of the present literatures investigates the effects of voids on delamination growth under compression.
In this research, a parametric study is performed to investigate the effects of voids on delamination growth in composite laminates under compression. In composite structures, delamination would be created by eccentricities in structural load path, structural discontinuities, and during manufacturing and maintenance processes. Also, the service damage such as the impact of foreign objects may also result in delamination. In the Finite Element model developed, a through-width surface delamination is assumed, and void is placed in critical locations ahead of crack tip. Strain Energy Release Rate (SERR) is calculated by the Virtual Crack Closure Technique (VCCT) in order to study the delamination growth. It is found that the delamination front experiences a mixed-mode delamination behavior when local out-of-plane buckling occurs. During the loading, Mode II SERR increases monotonically while Mode I SERR increases first and then decreases as the delamination front starts to close. Meanwhile, Mode II SERR is found to be much larger than the Mode I component. The presence of void does not significantly alter the transverse displacement of the delaminated part. However, the presence of void increases the Mode II SERR, as well as the total SERR, and this increase depends on the size and location of void. For Mode I SERR, the effect of void is not that prominent.
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Characterising failure of structural materials using digital imagesConradie, Johannes Hendrik 03 1900 (has links)
Thesis (MEng)--Stellenbosch University, 2015. / ENGLISH ABSTRACT: The fracture of ductile materials is currently regarded as a complex and challenging
phenomenon to characterise and predict. Recently, a bond-based, non-local theory was
formulated called the peridynamic theory, which is able to directly solve solid mechanics
problems that include fracture. The failure criterion is governed by a critical stretch
relation between bonds. It was found in literature that the critical stretch relates to the
popular fracture mechanics parameter called the critical energy release rate for predicting
brittle linear-elastic failure. It was also proposed that the non-linear critical energy
release rate or J-integral can be used to model ductile failure using peridynamics.
The aim of this thesis was to investigate the validity of using the J-integral to determine
the critical stretch for predicting ductile failure. Standard ASTM fracture mechanics
tests on Compact Tension specimens of Polymethyl methacrylate, stainless steel 304L
and aluminium 1200H4 were performed to determine the critical energy release rates
and non-linear Resistance-curves. Furthermore, a novel peridynamic-based algorithm
was developed that implements a critical energy release rate based failure criterion and
Digital Image Correlation (DIC) measured full surface displacement fields of cracked
materials. The algorithm is capable of estimating and mapping both the peridynamic
damage caused by brittle cracking and damage caused by plastic deformation. This
approach was used to validate the use of an energy release rate based failure criterion
for predicting linear-elastic brittle failure using peridynamics. Also, it showed a good
correlation among the test results for detecting plastic damage in the alloys when incorporating
the respective J-integral derived critical stretch values. Additionally, Modified
Arcan tests were performed to obtain Mode I, Mode II and mixed Mode fracture load
results of brittle materials. Mode I peridynamic models compared closely to test results
when using the Mode I critical energy release rate, derived critical stretch and served
as validation for the approach. Moreover, it was argued that Mode I failure criteria
cannot in principle be used to model shear failure. Therefore, it was proposed to rather
use the appropriate Mode II and mixed Mode critical energy release rates to predict the
respective failures in peridynamics. Also, for predicting ductile failure loads it was found
that using a threshold energy release rate derived from the R-curve yielded considerably
more accurate failure load results compared to the usage of the critical energy release
rate, i.e. J-integral.
In this thesis it was shown that there exists great potential for detecting and characterising
cracking and failure by using a peridynamic-based approach through coupling DIC
full displacement field measurements and the critical energy release rate of a particular
structural material. / AFRIKAANSE OPSOMMING: Duktiele breeking van materiale word tans beskou as 'n kompleks- en uitdagende fenomeen
om te voorspel en te karakteriseer. 'n Binding-gebaseerde, nie-lokale teorie is onlangs
geformuleer, genaamd die peridinamika teorie. Die laasgenoemde stel ons in staat om
soliede meganiese probleme met krake direk op te los. Die falings kriterium word bemagtig
deur die kritiese strekfaktor tussen verbindings. Daar was bewys dat die kritiese
strekfaktor in verband staan met die popul^ere breek meganika parameter, genaamd die
kritiese vrylatings-energie-koers vir die voorspelling van bros line^ere-elastiese faling. 'n
Onlangse verklaring meen dat die kritiese strekfaktor vir duktiele falingsgedrag, bereken
kan word met die nie-line^ere kritiese vrylatings-energie-koers, beter bekend as die J-
integraal.
Die doel van hierdie tesis was om te meet hoe geldig die gebruik van die J-integraal
is om die kritiese strekfaktor te bereken, om sodoende duktiele breking te ondersoek.
Standaard ASTM breukmeganika toetse op Polimetilmetakrilat, vlekvrye staal 304L en
aluminium 1200H4 is uitgevoer om die kritiese vrylatings-energie-koers en Weerstandskurwes
te bepaal. Verder was 'n nuwe peridinamies-gebaseerde algoritme ontwikkel.
Die laasgenoemde implementeer die berekening van 'n kritiese strekfaktor, gebaseer
op die kritiese vrylatings-energie-koers, sowel as Digitale Beeld Korrelasie (BDK) vol
oppervlaks-verplasings veld metings van gebreekte materiale. Dit is in staat om die
peridinamiese skade te bereken, tesame met die beeld wat veroorsaak was van bros
krake en plastiese vervorming in duktiele materiale. Hierdie benadering is aangewend
om die gebruik van 'n vrylatings-energie-koers gebaseerde falings kriterium vir bros
line^ere-elastiese falings in peridinamika te bekragtig. 'n Goeie korrelasie tussen toets
resultate is ook gevind vir die opsporing van skade wat veroorsaak is deur plastiese
deformasie in die legerings waar die onderskeilike J-integrale gebruik was as falings kriteria.
Daarbenewens, was Verandere Arcan toetse uitgevoer om die Modes I, Modes II
en gemenge Modes falingsresultate te verkry. Die Modes I peridinamiese model het goed
vergelyk met die toetsresultate en het gedien as bekragtiging vir die falingsbenaderings.
Verder was dit aangevoer dat Modes I falings kriterium in beginsel nie gebruik kan
word om skuiffaling te modelleer nie. Dus was dit voorgestel om eerder die toepaslike
Modes II en gemengde Modes kritieke vrylatings-energie-koerse te gebruik om onderskeie
falings te voorspel in peridinamiese modelle. Dit was ook gevind dat vir die voorspelling
van duktiele falingslaste die drumpel vrylatings-energie-koers, wat verkrygbaar is vanaf
die Weerstands-kurwe, aansienlik meer akkurate resultate gee, in vergelyking met die
gebruik van die kritiese vrylatings-energie-koers, m.a.w. die J-integraal.
In hierdie tesis was dit gewys dat daar groot potensiaal bestaan vir die opsporing en
karakterisering van krake en falings met 'n peridinamies-gebaseerde benadering, deur dit
te skakel met BDK vol verplasings veld metings en die kritiese vrylatings-energie-koers
van 'n bepaalde strukturele materiaal.
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Effect of Pore Size and Thickness on Critical Pressure of Elastic SystemsCarter, Barton P. 19 July 2005 (has links)
Significant energy savings can be achieved by improving efficiency of water removal in the press section of a paper machine, rather than energy-intensive evaporative dryer cans. Impulse drying is a novel technology to remove water from the sheet in the press section by using a heated press roll.
Delamination is a major challenge to be overcome before impulse drying can be implemented successfully. Delamination is caused by a region of high temperature liquid water under high pressure in the press. Upon exiting the nip, the pressure drops and the high temperature water flashes to steam. If the expansion of the steam is too strong, the bonds between the fibers will fail and a blister will form. The formation of this blister is characteristic of delamination.
The goal of this project was to understand the internal mechanics of a wet web as it exits the nip of an impulse dryer. In this way, the components of the sheet can be tailored to open the operating window of impulse drying. A mathematical model, developed to describe the deflection and delamination of an elastic membrane, was utilized in this work. Three failure criteria were employed to represent delamination of this pliable membrane from the more rigid sub layers in the sheet.
The experimental portion of this effort was devoted to showing the validity of these models and which was the best fit. A series of experiments were employed to validate the model. A peel test was used to determine the amount of work needed to pull a membrane from a rigid substrate. Pressurized blister experiments were conducted to find the relationship between critical pressure and initial defect size. The predictions from the mathematical model were then compared to these experimental values. Finally, work was done to understand the physics of the delamination of a porous membrane.
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A Study of The Mixed-Mode Fracture of Molding Compound-Substrate Interface of IC PackageHuang, Ming-Yeong 22 August 2003 (has links)
Abstract
The interface crack of an IC package is easily existed under vibration, high temperature or collision. Its reliability will be reduced significantly for the existence of the crack. This study, therefore, is to investigate the fracture mechanism of the underfill/substrate interface with different crack length.
In this study, mixed mode fracture of the underfill/substrate interface, was investigated by single lap tension test. Based on the load-displacement curve, J integral, energy release rate and stress intensity factor were calculated. Moreover, the relationships among the stress intensity facto KI, KII and phase angle were also derived.
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Initiation and propagation of transverse cracking in composite laminatesYe, J., Lam, Dennis, Zhang, D. January 2010 (has links)
The matrix cracking transverse to loading direction is usually one of the most common observations of damages in composite laminates. The initiation and propagation of transverse cracks have been a longstanding issue in the last few decades. In this paper, a three-dimensional stress analysis method based on the state space approach is used to compute the stresses, including the inter-laminar stresses near transverse cracks in laminated composites. The stress field is then used to estimate the energy release rate, from which the initiation and propagation of transverse cracking are predicted. The proposed method is illustrated by numerical solutions and is validated by available experimental results. To the best knowledge of the authors, the predictions of crack behaviour for non-symmetrical laminates and laminates subject to in-plane shearing are presented for the first time in the literature.
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Fracture Mechanics of High Performance Nylon FibersAverett, Rodney Dewayne 12 April 2004 (has links)
A fracture mechanics protocol appropriate for small fibers (35 micron diameter) is presented, which allows for the determination of the strength limitations of high performance nylon 6,6 fibers. Specifically, linear elastic fracture mechanics (LEFM) techniques are employed in addition to elastic-plastic fracture mechanics (EPFM) theories to achieve this.
We assume that a minute semi-elliptical flaw of an unknown size exists in the specimen, as a result of the detrimental effects of the manufacturing process (melt spinning). Next, we seek to propagate this flaw in a stable manner through an ancillary process such as high cycle or low cycle fatigue (load-unload). After propagation, uniaxial tensile experiments are performed on the fatigued samples, by which the crack growth eventually becomes catastrophic during the process. After performing scanning electron microscopy (SEM) techniques and reviewing fractography, we are able to determine the critical flaw size and ligament length that leads to unstable crack propagation. These results are substituted into the appropriate LEFM equations and are in close agreement with material properties for nylon 6,6. A discussion is provided that draws parallel to the topics discussed in the literature investigation and the experimental results of this study.
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高強度GFRPのモードⅢ層間はく離疲労き裂進展におよぼす応力比の影響松原, 剛, MATSUBARA, Go, 田中, 啓介, TANAKA, Keisuke 05 1900 (has links)
No description available.
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高強度GFRP積層板の層間はく離疲労き裂進展におよぼす混合モード比の影響松原, 剛, MATSUBARA, Go, 西川, 弘泰, NISHIKAWA, Hiroyasu, 仁瓶, 寛太, NIHEI, Kanta, 田中, 啓介, TANAKA, Keisuke 12 1900 (has links)
No description available.
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高強度GFRPのモードⅠ層間はく離疲労き裂進展におよぼす繊維架橋の影響松原, 剛, MATSUBARA, Go, 尾野, 英夫, ONO, Hideo, 田中, 啓介, TANAKA, Keisuke 07 1900 (has links)
No description available.
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高強度GFRPのモードⅡ層間はく離疲労き裂進展におよぼす応力比の影響松原, 剛, MATSUBARA, Go, 尾野, 英夫, ONO, Hideo, 田中, 啓介, TANAKA, Keisuke 04 1900 (has links)
No description available.
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