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1
Morsi, Khaled M. B. E. "Mechanical properties of particle reinforced alumina." Thesis, University of Oxford, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.320644.
Full text
2
Ma, Wei. "Fracture toughness characterization of thin Ti/SiC composites." Thesis, Cranfield University, 2011. http://dspace.lib.cranfield.ac.uk/handle/1826/9324.
Full textAbstract:
Titanium based alloys reinforced uniaxially with silicon carbide fibres (Ti/SiC)
are advanced and innovative materials for aerospace vehicles. To avoid
potential problems, these new materials should be extensively tested and
analyzed before application.
This research focuses on experimental fracture toughness study on 0.5 mm
thick Ti/SiC composite materials for aerospace applications. The fracture
toughness tests are mainly based on BS 7448 with some modifications for
transversely isotropic behaviour of the composite materials.
By loading on specimens in the direction perpendicular to the fibre axis, three
critical values of fracture toughness parameters characterizing fracture
resistance of material, plane strain fracture toughness [Plane strain fracture toughness
}, critical crack tip
opening displacement [Critical crack tip opening displacement
] and critical J-integral [Critical at the onset of brittle crack extension or pop-in when
Δa is less than 0.2 mm.
]are measured for two
kinds of titanium alloy specimens and three kinds of Ti/SiC composites
specimens.
The values of [Provisional value of Plane strain fracture toughness
] obtained from the fracture toughness tests are not valid [Plane strain fracture toughness
]
for these materials, since the thickness of specimens is insufficient to satisfy the
minimum thickness criterion; however, the results could be used as particular
critical fracture toughness parameter for 0.5 mm thick structures of the materials.
The valid values of [Critical J at the onset of brittle crack extension or pop-in when
Δa is less than 0.2 mm.
] and [Critical crack tip opening displacement
] could be used as fracture toughness
parameters for all thickness of structures of the materials. The results also show
that: fracture toughness of the titanium alloys decreases dramatically after being
unidirectional reinforced with SiC fibre, which is mainly triggered by poor
fibre/matrix bonding condition. Moreover, Ti-Al3-V2.5 reinforced with 25%
volume fraction SiC fibre performs better than the other two composites in
fracture resistance.
3
Tsikopoulos, Nicholas. "Toughness and factors in graphs." Thesis, McGill University, 1987. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=59616.
Full textAbstract:
The author proved independently, every 2-tough graph is hamiltonian (3), that if G is a K-tough graph with n vertices and if kn is even then G has a k-factor (4) is best possible by showing that for every positive integer k and for every positive $ varepsilon$ there is a (k-$ varepsilon$)-tough graph G with no k-factor; furthermore, if k is odd then G can be made to have an even number of vertices; this result makes chapter 1 of the present thesis.Enomoto elaborated further on the subject and gave two results, in (4) and (5) respectively, which are improvements over (4):
(5) provided that k$ vert$G$ vert$ is even and $ vert$G$ vert sbsp{=}{>}$ k + 1, G has a k-factor if, for each set S of vertices, G-S has at most $ vert$S$ vert$/k + 7/8 components; and (6) provided that k$ vert$G$ vert$ is even and $ vert$G$ vert sbsp{=}{>}$ k$ sp{2}$ + 1, G has a k-factor if, for each set S of vertices, G-S has at most $ vert$S$ vert$/k + 1 components. The proofs of (4), (5) and (6) make chapters 2, 3 and 4 respectively.
4
Stamp, Elizabeth. "Mental toughness and health-related lifestyle factors." Thesis, University of Lincoln, 2017. http://eprints.lincoln.ac.uk/28659/.
Full textAbstract:
Mental toughness (MT) originated within elite sport and was identified as an attribute of success. MT has emerged as being important for enhancing health-related lifestyle factors (HRLF; e.g., physical activity). Investigating the healthiness of one’s lifestyle appears a timely area to research given the current health status of the population. Therefore, the aim of this thesis was to investigate MT in relation to HRLF and weight loss. Study One investigated MT and HRLF in university students (n = 167). Self-reported MT, physical activity, exercise barriers, dietary behaviour, and psychological wellbeing were recorded. MT was significantly different between regular exercisers (M = 3.43 ± .42) and non-regular exercisers (M = 3.24 ± .54, p < .05). Components of eating identity, exercise barriers, and psychological wellbeing, were significantly correlated with MT. Study Two longitudinally investigated weight loss progress, and adherence to a weight loss support group, in slimming club members who were pursuing a weight loss goal (n = 132). MT and eating identity were assessed at baseline, three-months, and six-months, and weight was recorded at weekly meetings. Overall MT was not significantly related to weight loss (r = -.15, p > 0.05) or adherence to the service (r = .03, p > 0.05). Study Three sampled individuals who held a weight loss goal, but were not attending a weight loss support club (n = 78). Overall MT was not significantly related to weight loss (r = -.21, p > 0.05). MT was not significantly different between weight loss goal achievers (M = 3.62 ± .49) and non-goal achievers (M =3.42 ± .38, p > 0.05). Thus, irrespective of whether structured support is received, overall MT was not related to weight loss progress. II Study Four investigated the experiences of high (n = 9) and low (n = 7) mentally tough individuals pursing a weight loss goal. High and low MT individuals, identified using the MTQ48, were interviewed. Thematic analysis revealed that amongst the high mentally tough individuals, those who prioritised leading a healthy lifestyle reported weight loss success compared to those who prioritised other goals. Strategies to overcome low levels of MT (e.g., control), as well as receive additional support, appeared crucial for successful weight loss in low MT individuals. Study Five further investigated the low MT individuals’ (n = 7) perceptions, experiences, and attitudes, towards weight loss. Low MT individuals were sampled based on their MT score assessed via the MTQ48. Vignette based interviews extended the findings in Study Four. Thematic analysis revealed key findings, including the potential to change low MT individuals’ perceptions to enhance behaviour change. Overall, this thesis expanded the understanding of MT; the processes that one experiences when trying to lose weight appears to differentiate between high and low MT individuals, which offers an explanation as to why MT did not appear to play a significant role in weight loss outcomes. These findings challenged the predominant contemporary understanding of MT and demonstrated that MT was not associated with behaviour change to achieve weight loss.
5
Stonkus, Mark. "The development and validation of the Inventory of Mental Toughness Factors in Sport (IMTF-S)." Thesis, Boston University, 2011. https://hdl.handle.net/2144/32837.
Full textAbstract:
Thesis (Ed.D.)--Boston UniversityPLEASE NOTE: Boston University Libraries did not receive an Authorization To Manage form for this thesis or dissertation. It is therefore not openly accessible, though it may be available by request. If you are the author or principal advisor of this work and would like to request open access for it, please contact us at open-help@bu.edu. Thank you.
The purpose of this study was to develop and validate a new measure of mental toughness in sport. The role of mental toughness in sport has been characterized as key in assisting athletes to obtain success by optimizing practice, overcome failures, and develop the mental skills necessary to win (Norris, 1999). A literature review concluded with six concepts (hardiness, coping, self-efficacy, mindset, resilience, and optimism) being used to develop an 80-item instrument measuring mental toughness on a 5-point Likert scale (always-never). Athletes (N=359, 195 males, 164 females, mean age = 17.57, SD = 3.4) drawn from a variety of sports were administered the Inventory of Mental Toughness Factors in Sport (IMTF-S) during the spring of 2011. Item analysis and principal component analysis yielded a four-factor 48-item model with an overall reliability (Cronbach's alpha) score of .925. The mental toughness factors and corresponding reliability scores were labeled as follows: Identification (.933), Negation (.812), Determination (.765), and Motivation (.890). Test-retest reliability measures were also obtained on a sample of 25 athletes (r= .892). Concurrent validity was demonstrated (r= .798, p ≤ .001) by comparing a set of scores (N= 75) on the IMTF-S and the Psychological Performance Inventory (PPI; Loehr, 1986). Predictive validity was assessed by comparing means of three sample's scores with ratings of their respective coaches. One independent samples t-test on a high school boys lacrosse team (N=18) indicated that the IMTF-S may have predictive properties (p= .021), however two other samples (women's elite field hockey, N=19) and junior A ice hockey (N=24) revealed non-significant findings when coaches ratings were compared to athlete self-assessment. Finally, correlation analysis found no significant relationships between mental toughness and age or experience. The results of this study provide empirical evidence for the valid use of the IMTF-S in measuring mental toughness in athletes. Perhaps of greater importance is that this study bolsters the existing research on mental toughness and further promotes its identification and development in assisting athletes in overcoming high-pressured and adverse conditions in their sporting environments.
2031-01-01
6
Gwin, Mary Elizabeth. "Factors affecting the impact toughness of ultra low carbon steel weld metal." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 1996. http://handle.dtic.mil/100.2/ADA320665.
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7
Alpay, Ceyda. "Investigation Of Geometrical Factors For Determining Fracture Toughness With The Modified Ring Test." Master's thesis, METU, 2008. http://etd.lib.metu.edu.tr/upload/12609883/index.pdf.
Full textAbstract:
Modified Ring specimens are of the shape of discs having a hole inside and
flattened ends. These specimens are used for determination of Mode I fracture
toughness. Finite element program, named ABAQUS, is used for numerical
modeling for finding stress intensity factors. Varying disc geometries were used
for the experiments and numerical modeling in which size of the flat ends,
radius of the hole inside, and external radius of the specimen were varied.
Experiments were done by using pink Ankara andesite. Effects of internal hole
radius, external disc radius and size of the flat ends on both stress intensity
factor and fracture toughness were studied. In order to compare the results,
fracture tests with semi-circular specimens under three point bending (SCB)
were also performed. From a similar previous study, fracture toughness values
of gray andesite were recalculated and compared to the fracture toughness
values of pink andesite for varying geometrical factors. Size effect studies were
performed as well for varying diameter of core specimens.Fracture toughness values of andesite were found to increase with increasing
specimen size. Fracture toughness of 100 mm specimens was determined as
1.11±0.07 MPa&
#8730
m, whereas fracture toughness of 75 mm specimens was 0.96±
0.08 MPa&
#8730
m. 100 mm or larger diameter specimens were suggested for the fracture toughness determination with the modified ring tests.
8
Het, Kivanc. "Effects Of Geometrical Factors On Fracture Toughness Using Semi-circular Bending Type Specimens." Master's thesis, METU, 2008. http://etd.lib.metu.edu.tr/upload/12609320/index.pdf.
Full textAbstract:
Semi-circular specimens (SCB) under three point-bending which are commonly used for fracture testing of rocks were used here for fracture mechanics tests. A total of 65 specimens were tested by using Ankara andesite rock.
Investigations including the effects of initial notch thickness, different loading span ratios (S/R), flattened loading end, and little dimensional variations when preparing the specimens were carried out.
Stress intensity factors for specimens with different geometries were computed individually by using a 3D finite element program ABAQUS.
Specimens with a preliminary notch thickness varying from 0.84 to 3.66 mm were tested under three point bending.
For a second group of specimens loading span was changed and fracture toughness variation was studied. Another change in the specimen geometry was made by machining a flat loading end at the upper load application point. Fracture toughness values were computed using the stress intensity values computed from numerical modeling and failure loads from the experiments.
It was found that up to 2 mm fracture toughness was not affected by variations in the thickness of preliminary notches. Fracture toughness was not affected by changing the loading span. For specimens with flat loading ends, fracture toughness was about 16% lower than the value found from regular SCB type specimens loaded at a point at the top by a steel roller.
As a result of about 46 experiments average fracture toughness of Ankara Gölbasi andesite was found as 1.36 MPa .
9
Van, Slyke Jonathon J. "Factors affecting the strength and toughness of ultra-low carbon steel weld metal." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 1999. http://handle.dtic.mil/100.2/ADA374133.
Full textAbstract:
Thesis (Degree of Mechanical Engineer) Naval Postgraduate School, December 1999."December 1999". Thesis advisor(S): A.G. Fox. Includes bibliographical references (p. 63-64). Also available online.
10
Baker, Frank W. Jr. "Mental Toughness: Effect on Factors Associated with Injury and Illness in Adolescent Athletes." Ohio University / OhioLINK, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1407271208.
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11
Alkilicgil, Cigdem. "Development Of Specimen Geometries For Mode I Fracture Toughness Testing With Disc Type Rock Specimens." Phd thesis, METU, 2010. http://etd.lib.metu.edu.tr/upload/12611985/index.pdf.
Full textAbstract:
Flattened Brazilian disc and modified ring test methods are attractive methods being simpler compared to the other mode I fracture toughness testing methods on rock cores. The aim of this study is to improve these simple methods to yield fracture toughness values that are close to the ones determined by the suggested methods. ABAQUS finite element program was used to determine stress intensity factors of models with various dimensions. Comparing fracture toughness to the results obtained by semicircular bending method tests (0.94 MPa√
m for andesite and 0.56 MPa&
#8730
m for marble) and the cracked chevron notched Brazilian disc method tests (1.45 MPa&
#8730
m for andesite and 1.08 MPa&
#8730
m for marble), proper geometrical parameters were investigated by changing diameter, central-hole diameter, and loading angle of Ankara andesite and Afyon marble specimens. Semicircular bending method results were lower than the cracked chevron notched Brazilian disc method results. With flattened Brazilian disc method, the closest results (1.45 MPa&
#8730
m for andesite and 1.12 MPa&
#8730
m for marble) to the suggested method was obtained by 54 mm diameter discs with loading angles between 32.5°
and 38.0°
and with thicknesses between 19 mm and 34 mm. With modified ring test on andesite, the closest results to the suggested method was obtained by 75 mm diameter discs with 8 mm central-hole diameter and 25°
loading angle (1.47 MPa&
#8730
m for andesite and 1.07 MPa&
#8730
m for marble), and with 14 mm central-hole diameter and 16°
loading angle (1.50 MPa&
#8730
m for andesite and 1.05 MPa&
#8730
m for marble).
12
Sener, Karakas Sinem. "Shear Mode Rock Fracture Toughness Determination With A Circular Plate Type Specimen Under Three-point Bending." Phd thesis, METU, 2011. http://etd.lib.metu.edu.tr/upload/12613036/index.pdf.
Full textAbstract:
Fracture toughness is an important rock property for rock fracturing and fragmentation applications. Theory and practice of opening mode (mode I) and shearing mode (mode II) fracture toughness tests are still in a developing stage for the cylindrical rock cores. A new circular plate type test specimen is used for mode II fracture toughness testing on rock cores. This involves a straight edge notched circular plate type core disc geometry under three-point bending loadnew method and its associated specimen geometry is referred as straight edge notched disc bend (SNDB) specimen under three-point bending. Mode II fracture toughness results of the tests with this new geometry were compared to the results of the tests commonly employed for mode II fracture toughness testing. Specimen geometries were modeled and mode II stress intensity factors were computed by finite element modeling using ABAQUS program. For comparison purposes, mode II or shearing mode fracture toughness KIIc of two different rock types were determined by different testing methods commonly employed in recent practice. Core specimens of Ankara andesite and Afyon marble rock types were tested with cracked chevron notched Brazilian disc and cracked straight through Brazilian disc specimens under Brazilian type loading, semi-circular bend specimen and straight edge notched disc bending specimen geometries under three-point bending.For all testing groups, cylindrical cores with diameters varying from 7.5 cm to 12.5 cm were prepared with notch lengths changing from 1.5 cm to 2.6 cm. Effect of specimen thickness on mode II fracture toughness was investigated for three different testing methods. Fracture toughness values remained constant when thickness of the specimens was increased for cracked straight through Brazilian disc, semi-circular bend and straight notched disc bend methods. For cracked straight through Brazilian disc method KIIc values of Ankara andesite and Afyon marble were 0.99 MPa&radic
m and 0.86 MPa&radic
m, respectively. Mode II fracture toughness with semi-circular bend specimen was 0.43 MPa&radic
m for andesite and 0.46 MPa&radic
m for marble. When the results of the two three-point bending type tests were compared straight notched disc under three-point bending resulted in higher KIIc values (0.61 MPa&radic
m for andesite and 0.62 MPa&radic
m for marble) than the results found by semi-circular bend tests.
13
Abendroth, Martin, and Eberhard Altstadt. "COVERS WP4 Benchmark 1 Fracture mechanical analysis of a thermal shock scenario for a VVER-440 RPV." Forschungszentrum Dresden, 2010. http://nbn-resolving.de/urn:nbn:de:bsz:d120-qucosa-28238.
Full textAbstract:
This paper describes the analytical work done by modelling and evaluating a thermal shock in a WWER-440 reactor pressure vessel due to an emergency case. An axial oriented semielliptical underclad/surface crack is assumed to be located in the core weld line. Threedimensional finite element models are used to compute the global transient temperature and stress-strain fields. By using a three-dimensional submodel, which includes the crack, the local crack stress-strain field is obtained. With a subsequent postprocessing using the j-integral technique the stress intensity factors KI along the crack front are obtained. The results for the underclad and surface crack are provided and compared, together with a critical discussion of the VERLIFE code.
14
Abendroth, Martin, and Eberhard Altstadt. "COVERS WP4 Benchmark 1 Fracture mechanical analysis of a thermal shock scenario for a VVER-440 RPV." Forschungszentrum Dresden-Rossendorf, 2007. https://hzdr.qucosa.de/id/qucosa%3A21650.
Full textAbstract:
This paper describes the analytical work done by modelling and evaluating a thermal shock in a WWER-440 reactor pressure vessel due to an emergency case. An axial oriented semielliptical underclad/surface crack is assumed to be located in the core weld line. Threedimensional finite element models are used to compute the global transient temperature and stress-strain fields. By using a three-dimensional submodel, which includes the crack, the local crack stress-strain field is obtained. With a subsequent postprocessing using the j-integral technique the stress intensity factors KI along the crack front are obtained. The results for the underclad and surface crack are provided and compared, together with a critical discussion of the VERLIFE code.
15
Pallaspuro, S. (Sakari). "On the factors affecting the ductile-brittle transition in as-quenched fully and partially martensitic low-carbon steels." Doctoral thesis, Oulun yliopisto, 2018. http://urn.fi/urn:isbn:9789526218977.
Full textAbstract:
Abstract From the largest discontinuities to the smallest of the elements, various factors can threaten structural integrity. Susceptibility to these factors elevates with higher yield strengths. As-quenched low-carbon steels with a martensitic or martensitic-bainitic microstructure are modern ultra-high-strength structural steels. They can possess sufficient toughness, formability, and weldability, and are typically used in weight-critical and high-performance structures. Common problems with as-quenched steels with a yield strength of 900 MPa or more are that they do not obey the conventional correlation between the fracture toughness reference temperature T₀ and the impact toughness transition temperature T₂₈ᴊ used in many standards and structural integrity assessment procedures, and a lack of design rules in general. This thesis studies the relationship between the T₀ and T₂₈ᴊ to provide additional knowledge for future standardisation, the microstructural features governing the toughness at these temperatures on both global and local scale, and whether hydrogen embrittlement is present at subzero temperatures. It uses steels produced via laboratory rolling and quenching as well as from pilot-scale and full-scale industrial production, studying them with standardised toughness tests, microstructural characterisation, fractography, and cohesive zone modelling. As-quenched steels have a distinct correlation between T₀ and T₂₈ᴊ. An improved general T₀ – T₂₈ᴊ correlation applies to a wide range of steels. T₂₈ᴊ correlates closely with a dynamic reference toughness, which can be used together with the fraction of detrimental {100} cleavage planes near the main fracture plain to effectively estimate the transition temperatures. On a local scale, centreline segregation decreases the effective coarse grain size, which more than compensates for the harmful effects associated with the higher hardness and inclusion content of the centreline, resulting in increased fracture toughness. Hydrogen embrittlement causes a decrease in fracture toughness and local deformability, thereby increasing T₀ while leaving T₂₈ᴊ unaffected. Overall, the results show that high toughness demands good control of effective coarse grain size and hydrogen contentTiivistelmä Tekijät suurimmista epäjatkuvuuskohdista aina pienimpään alkuaineeseen voivat uhata rakenteellista eheyttä, minkä lisäksi alttius näille kasvaa materiaalin myötölujuuden kasvaessa. Modernit karkaistun tilan ultralujat matalahiiliset rakenneteräkset voivat silti omata riittävän sitkeyden, muovattavuuden ja hitsattavuuden. Tyypillisiä käyttökohteita näille ovat painon suhteen kriittiset ja korkean suorituskyvyn rakenteet. Yleinen ongelma myötölujuudeltaan noin ja yli 900 MPa karkaistun tilan teräksillä on se, että ne eivät noudata perinteistä murtumissitkeyden referenssilämpötilan T₀ ja iskusitkeyden transitiolämpötilan T₂₈ᴊ välistä korrelaatiota, jota käytetään useissa standardeissa ja suunnitteluohjeissa, jotka eivät myöskään vielä salli näin lujien terästen käyttöä. Tämä väitöstyö tutkii transitiolämpötilojen T₀ ja T₂₈ᴊ välistä suhdetta edistääkseen näiden terästen sisällyttämistä standardeihin, haurasmurtuma-sitkeyteen vaikuttavia mikrorakenteellisia tekijöitä sekä yleisellä että paikallisella tasolla, ja vetyhaurautta matalissa lämpötiloissa. Koeteräkset ovat laboratoriovalmisteisia, tuotantokokeita ja tuotantolaatuja. Niitä tutkitaan standardisoiduilla sitkeyskokeilla, mikrorakenteen karakterisoinnilla, fraktografialla ja koheesiovyöhykettä hyödyntävällä mallinnuksella. Tulokset osoittavat karkaistun tilan terästen omaavan erityisen korrelaation T₀ ja T₂₈ᴊ välillä. Muokattu, ultralujat teräkset huomioiva yleinen T₀ – T₂₈ᴊ -korrelaatio soveltuu laajalti eri terästyypeille. T₂₈ᴊ korreloi läheisesti dynaamisen referenssisitkeyden kanssa, jonka avulla yhdessä haitallisten {100} lohkomurtumatasojen osuuden kanssa voidaan estimoida joukko transitiolämpötiloja. Paikallisella tasolla keskilinjasuotauma pienentää efektiivistä karkeiden rakeiden kokoa, mikä suotauman suurista sulkeumista ja kovuudesta huolimatta parantaa murtumissitkeyttä. Vetyhauraus taas huonontaa sitkeyttä ja paikallista muodonmuutoskykyä myös matalissa lämpötiloissa nostaen T₀ lämpötiloja. Kokonaisuutena erinomainen transitiolämpötilasitkeys vaatii efektiivisen karkearaekoon ja vetypitoisuuden minimointia
16
Alkilicgil, Cigdem. "Development Of A New Method For Mode I Fracture Toughness Test On Disc Type Rock Specimens." Master's thesis, METU, 2006. http://etd.lib.metu.edu.tr/upload/12607513/index.pdf.
Full textAbstract:
A new testing method was introduced and developed to determine Mode I fracture toughness of disc type rock specimens. The new method was named as Straight Notched Disc Bending and it uses disc specimens under three-point bending. 3D Numerical modeling was carried out with a finite element program ABAQUS to find stress intensity factors for both well-known Semi-circular Bending specimen models and Straight Notched Disc Bending specimen models for varying disc geometries. Both specimen types included notches where a crack front is introduced at the tip of the notch to compute the stress intensity factors. For stress intensity analysis, crack front-upper loading point distance and span length between the two roller supports at the bottom boundary of the specimens were changed.
Fracture toughness testing was carried on Ankara GölbaSi pink colored andesite for both specimen types
crack front-upper loading point distance and span length between the two roller supports at the bottom boundary of the specimens were changed during the tests. For both specimen geometries, notch lengths changing from 5 mm to 20 mm were used. For each notch length, two different roller supports with span lengths 60 mm and 70 mm were used. For both methods, fracture toughness values determined by using numerically computed stress intensity factors and failure loads obtained from the experiments were very close
the new method was verified by comparing the results. The new method had advantages of lower confining pressure at the crack front and lower stress intensities with a possible smaller crack tip plasticity region.
17
Tez, Burkay Yasar. "Effects Of Specimen Height And Loading Span On The Fracture Toughness Of Disc Type Rock Specimens Under Three Point Bending." Master's thesis, METU, 2008. http://etd.lib.metu.edu.tr/upload/12609496/index.pdf.
Full textAbstract:
A relatively new fracture toughness testing method called Straight Notched Disc Bending (SNDB) was used before for fracture testing of Ankara Andesite and Afyon Marble cores. In this work to investigate the applicability of the new method to other rock types. With a preliminary notch of 10 mm, straight notched disc type specimens with a diameter of 75 mm were loaded by three-point bending loads.
Investigation of effect of specimen height on the stress intensity factor and fracture toughness was carried out. Specimen heights (B) between 18 &ndash67 mm were tried for andesite and marble cylindrical specimens. Loading span, that is span/radius (S/R) ratio was changed between 0.6 - 0.9 for andesite specimens. Stress intensity factor for specimens was computed with ABAQUS program. Stress intensity factor was found to increase with increasing specimen diameter for a fixed span/radius ratio. Stress intensity factor decreased with increasing specimen height. Changing span was found to have no significant effect on fracture toughness of andesite. Fracture toughness was significantly lower for specimens with smaller height. The suggested testing height interval for this type of specimens was between height/diameter ratios of 0.49 &ndash
0.64. Results were compared to the results obtained by a well-known specimen geometry named semi-circular bend specimens (SCB) under three-point bending. SCB tests produced lower values for fracture toughness for both rock types. Fracture toughness was 0.99 MPa&
#8730
m for Ankara Andesite and 0.70 MPa&
#8730
m for Afyon Marble.
18
Alkoles, Omar M. S. "Mechanical behaviour and fracture toughness of unfilled and short fibre filled polypropylene both drawn and undrawn. Experimental investigation the effect of fibre content and draw ratio on the mechanical properties of unfilled and short glass fibre filled polypropylene." Thesis, University of Bradford, 2011. http://hdl.handle.net/10454/5510.
Full textAbstract:
The goal of this research is to investigate the combined effects of glass fibre reinforcement and molecular orientation in polypropylene-short glass fibre composites. Specimens have been fabricated using the injection moulding process and drawn using a small die drawing rig. The effects of die drawing on the fibre composites are complex, with the drawing process orienting both the polymer molecules and the glass fibres. This may be accompanied by the creation of voids in the polymer matrix and their destruction in the compressive stress field thus restoring the interfacial contact area between fibre and matrix. Unfilled and short glass fibre filled polypropylene specimens, with fibre content 7% wt, 13%wt, 27%wt, and 55%wt, were injection moulded prior to the die drawing process. An experimental program of die drawing within an oven at elevated temperature was conducted for polypropylene filled to various levels and at different strain rates. The specimens drew to draw ratios in the range ¿=1.41 to ¿=5.6. Mechanical characterization of the test materials has been conducted by examining the tensile stress strain and fracture behaviour under uniaxial conditions. The influence of glass fibre content and drawing conditions (draw ratio) on the fracture toughness and crack propagation was investigated using the double edge notched fracture test. The notch lengths ranged from 1.5 to 2.5 mm for 10 mm wide specimens. The critical stress intensity factor increased as the fibre content increased up to a limiting filler level. The fracture toughness of both unfilled and fibre filled polypropylene were found to be highly dependent on draw ratio. The results were analysed to find out the optimal draw ratio and fibre content that yielded the maximum modulus, strength and fracture toughness. Data showed that, at a given draw ratio, modulus, strength and fracture toughness increased with increasing fibre content to a maximum and then decreased. The optimum material was obtained at a draw ratio of 2.5 and filler loading 13wt%.
19
Alkoles, Omar M. "Mechanical behaviour and fracture toughness of unfilled and short fibre filled polypropylene both drawn and undrawn : experimental investigation of the effect of fibre content and draw ratio on the mechanical properties of unfilled and short glass fibre filled polypropylene." Thesis, University of Bradford, 2011. http://hdl.handle.net/10454/5510.
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The goal of this research is to investigate the combined effects of glass fibre reinforcement and molecular orientation in polypropylene-short glass fibre composites. Specimens have been fabricated using the injection moulding process and drawn using a small die drawing rig. The effects of die drawing on the fibre composites are complex, with the drawing process orienting both the polymer molecules and the glass fibres. This may be accompanied by the creation of voids in the polymer matrix and their destruction in the compressive stress field thus restoring the interfacial contact area between fibre and matrix. Unfilled and short glass fibre filled polypropylene specimens, with fibre content 7% wt, 13%wt, 27%wt, and 55%wt, were injection moulded prior to the die drawing process. An experimental program of die drawing within an oven at elevated temperature was conducted for polypropylene filled to various levels and at different strain rates. The specimens drew to draw ratios in the range γ=1.41 to γ=5.6. Mechanical characterization of the test materials has been conducted by examining the tensile stress strain and fracture behaviour under uniaxial conditions. The influence of glass fibre content and drawing conditions (draw ratio) on the fracture toughness and crack propagation was investigated using the double edge notched fracture test. The notch lengths ranged from 1.5 to 2.5 mm for 10 mm wide specimens. The critical stress intensity factor increased as the fibre content increased up to a limiting filler level. The fracture toughness of both unfilled and fibre filled polypropylene were found to be highly dependent on draw ratio. The results were analysed to find out the optimal draw ratio and fibre content that yielded the maximum modulus, strength and fracture toughness. Data showed that, at a given draw ratio, modulus, strength and fracture toughness increased with increasing fibre content to a maximum and then decreased. The optimum material was obtained at a draw ratio of 2.5 and filler loading 13wt%.
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Xu, Shuangyan. "Evaluating Thermal and Mechanical Properties of Electrically Conductive Adhesives for Electronic Applications." Diss., Virginia Tech, 2002. http://hdl.handle.net/10919/27112.
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The objective of this study was to evaluate and gain a better understanding of the short-term impact performance and the long-term durability of electrically conductive adhesives for electronic interconnection applications. Three model conductive adhesives, designated as ECA1, ECA2 and ECA3, supplied by Emerson & Cuming, were investigated, in conjunction with printed circuit board (PCB) substrates with metallizations of Au/Ni/Cu and Cu, manufactured by Triad Circuit Inc.
Effects of environmental aging on the durability of conductive adhesives and their joints were evaluated. All the samples for both mechanical tests and thermal tests were aged at 85%, 100%RH for periods of up to 50 days. Studies of bulk conductive adhesives suggested that both plasticization, which is reversible and further crosslinking and thermal degradation, which are irreversible, might have occurred upon exposure of ECAs to the hot/wet environment. The durability of electrically conductive adhesive joints was then investigated utilizing the double cantilever beam (DCB) test. It was observed that the conductive adhesive joint was significantly weakened following hydrothermal aging, and there was a transition from cohesive failure to interfacial failure as aging continued. A comparative study of the durability of different conductive adhesive and substrate metallization combinations suggested that the resistance of the adhesive joints to moisture attack is related to the adhesive properties, as well as the substrate metallizations. It was noted that the gold/adhesive interface had better resistance to moisture attack than the copper/adhesive interface. A reasonable explanation of this phenomenon was given based upon the concept of surface free energy and interfacial free energy. XPS analysis was performed on the fractured surfaces of DCB samples. For adhesive joints with copper metallization, copper oxide was detected on the failed surfaces upon exposure of the conductive adhesive joints following aging. XPS analysis on the fractured surfaces of adhesive joints with Au metallization suggested that diffusion of Cu to the Au surface might have happened on the Au/Ni/Cu plated PCB substrates during aging.
The impact performance of conductive adhesives was quantitatively determined using a falling wedge test. This unique impact resistance testing method could serve as a useful tool to screen conductive adhesives at the materials level for bonding purpose. Moreover, this test could also provide some useful information for conductive adhesive development. This study revealed that the viscoelastic energy, which is a result of the internal friction created by chain motions within the adhesive material, played an important role in the impact fracture behavior of the conductive adhesives. This study also demonstrated that the loss factor, evaluated at the impact environment conditions, is a good indicator of a conductive adhesive's ability to withstand impact loading.Ph. D.
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Aguirre, Torrico Ivan Felix. "Tenacidade a fratura em condições elasto-plasticas com corpos de prova não normalisados para aços API 5L : analise numerica e experimental." [s.n.], 2006. http://repositorio.unicamp.br/jspui/handle/REPOSIP/264922.
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Orientador: Itamar FerreiraTese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecanica
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Resumo: O gasoduto Bolívia-Brasil foi fabricado com dutos de aços API 5L X65 e X70. Existem relatos na literatura especializada de que o campo de tensões nas vizinhanças da ponta da trinca e a tenacidade à fratura são similares entre os corpos de prova não normalizados do tipo tração com entalhe lateral [SE(T)] e dutos. Neste trabalho realizou-se um estudo numérico e experimental da tenacidade à fratura em condições elasto-plásticas, com corpos de prova do tipo SE(T), dos aços API 5L X65 e API 5L X70. A determinação dos parâmetros da mecânica da fratura elástica linear foi feita pelos Métodos dos Elementos Finitos (MEF) e dos Elementos de Contorno (MEC) e a determinação do parâmetro elasto-plástico integral J por MEF. O fator eta plástico obtido numericamente, pelo MEF e com dados fornecidos pelo método EPRI, foi de 1,0, para medições do deslocamento de abertura da boca da trinca (CMOD). Com este fator eta plástico, foram realizados ensaios experimentais de tenacidade à fratura com corpos de prova do tipo SE(T), com espessura de 5 mm, e esses valores foram comparados com os resultados de ensaios em corpos de prova de flexão em três pontos [SE(B)], também com espessura de 5 mm. Houve um boa concordância entre os resultados numéricos e experimentais da integral J. Verificou-se que as curvas J-R obtidas com ensaios SE(T) são próximas das obtidas com ensaios SE(B), tendo em vista que a espessura dos corpos de prova utilizada, de 5 mm, não pôde ser modelada no estado plano de tensão ou de deformação
Abstract: The gas pipeline Bolivia-Brazil was manufactured with pipes of API 5L X65 and X70 steels. Specialized literature report that the stress field in the neighborhood of the crack tip and the fracture toughness are similar between not standard single edge notch tensile specimens - SE(T) - and pipes. In this work numerical and experimental study were made of the elastic-plastic fracture toughness using SE(T) specimens for API 5L X65 and X70 steels. The determination of the parameters of the linear elastic fracture mechanics was performed by the methods of the Finite Elements (FEM) and Boundary Elements (BEM). The J-integral parameter was determined by FEM. The plastic eta factor was obtained by FEM and with data supplied by the EPRI method. In both cases for measurements of the crack mouth opening displacement (CMOD) the determined plastic eta factor is 1.0. With this plastic eta factor, experimental tests of fracture toughness were accomplished using SE(T) specimens with thickness of 5 mm, and those values were compared with the test results obtained with standard single edge bend -SE (B)- specimens also with thickness of 5 mm. There was a good agreement between the numeric and experimental results of J-integral. Was verified that the J-R curves obtained with SE(T) specimens are close to the obtained with SE(B) specimens
Doutorado
Materiais e Processos de Fabricação
Doutor em Engenharia Mecânica
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Taillebot, Virginie. "Contribition à l'étude de la rupture des alliages à mémoire de forme." Thesis, Besançon, 2012. http://www.theses.fr/2012BESA2026/document.
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Matériaux incontournables des matériaux fonctionnels, les alliages à mémoire de forme(AMF) peuvent présenter de très larges déformations réversibles. La Transformation de Phase Martensitique (TPM), ayant lieu lorsqu’il est soumis à une action mécanique ou thermique, lui confère des caractéristiques particulières. Le comportement thermomécanique des AMF est à présent bien maîtrisé. Cependant la connaissance de leur comportement `a la rupture reste un enjeu majeur pour leur dimensionnement dans le cadre de leur industrialisation pérenne. Ces travaux de recherche se sont attachés `a la connaissance, la description et la quantification du phénomène de localisation en pointe de fissure liée à la TPM induite sous contrainte, au travers du développement d’un modèle prédictif et de sa corrélation expérimentale par mesures de champs simultanées lors d’essais de rupture sur des éprouvettes fissurées de NiTi. Deux modèles analytiques basés sur la mécanique linéaire de la rupture, intégrant le caractère dissymétrique du comportement des AMF en traction/compression, ont été développés pour la prédiction des zones de transformation au voisinage de la pointe de fissure en tenant compte des différents modes de rupture ( élémentaires et mixtes I+II) et du rayon de courbure en pointe de fissure. Un banc de caractérisation par mesures simultanées de champs cinématiques par corrélation d’images (DIC) et thermique par thermographie infrarouge a été développé pour cartographier les champs expérimentaux d’essais de rupture en mode I sur des éprouvettes pré-fissurées. Cette bonne corrélation des modèles analytiques ouvre de nombreuses perspectives concernant l’analyse du couplage thermo mécanique associé à la TPM en pointe de fissure, l’enrichissement des modèles analytiques initiaux, et la confrontation avec les résultats expérimentaux pour des modes de rupture plus complexes (II et mixte I+II)Major player among functional materials, Shape Memory Alloys (SMA) may undergo verylarge reversible strain. SMA exhibit a Martensitic Phase Transformation (MPT) when they aresubmitted to mechanical or thermal actions, and that gives them some specific characteristics.The thermomechanical behavior of SMA is now well controlled. However, the knowledge of theSMA fracture behavior is a major challenge for their design and sizing for their sustainableindustrialization. This research project has focused on the understanding, describing and quantifyingof the phenomenon of localization at the crack tip due to stress-induced MPT. The study includestwo main aspects: the development of an analytical model and its experimental correlation bysimultaneous field’s measurements during tests on cracked NiTi specimens. Two analytical modelsbased on the linear fracture mechanics and those introduce the asymmetrical nature of the SMAbehavior in tension/compression, were developed for the prediction of transformation zones in thevicinity of the crack tip, taking into account the fracture mode (elementary and mixed ones)and the radii of curvature of the crack tip. A testbench with the measurement of simultaneouskinematic field with Digital Image Correlation (DIC) and thermal field with infrared thermographywas designed for mapping the experimental fields during fracture tests in mode I on pre-crackedspecimen. This good correlation of analytical models opens up many perspectives on the analysisof thermomechanical coupling associated with the MPT at the crack tip, the enrichment of the initialanalytical models, and comparison with experimental results for more complex failure modes (II andmixed I+II)
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Shipsha, Andrey. "Failure of Sandwich Structures with Sub-Interface Damage." Doctoral thesis, Stockholm, 2001. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-3184.
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Havlíková, Ivana. "Vyhodnocení lomových testů těles z vybraných stavebních materiálů pomocí modelu Dvojí-K." Doctoral thesis, Vysoké učení technické v Brně. Fakulta stavební, 2016. http://www.nusl.cz/ntk/nusl-355611.
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The purpose of dissertation is the analysis of the calculation of fracture parameters using Double-K fracture model for quasi-brittle specimens with the stress concentrator loaded by three-point bending or wedge splitting. To calculation of these parameters was used the developed DKFM_BUT software in Microsoft Excel application with using of Visual Basic programming language. Furthermore, the adequate shape functions and compliance functions were introduced for the selected wedge splitting test configurations. Main part of this dissertation is the series of comprehensively implemented and evaluated fracture experiments on specimens from advanced building materials, while the attention was paid to the analysis of experimental data. Finally, the selected results obtained using mentioned software support were presented and discussed.
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Lados, Diana Aida. "Fatigue crack growth mechanisms in Al-Si-Mg alloys." Link to electronic thesis, 2004. http://www.wpi.edu/Pubs/ETD/Available/etd-0204104-125758.
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Thesis (Ph. D.)--Worcester Polytechnic Institute.Keywords: Microstructure; Elastic-Plastic Fracture Mechanics; Crack closure; A356; J-integral; Conventionally cast and SSM Al-Si-Mg alloys; Residual stress; Heat treatment; Fatigue crack growth mechanisms; Threshold stress intensity factor; Plastic zone; Paris law; Fracture toughness; Roughness. Includes bibliographical references.