Dissertations / Theses on the topic 'Paper Elastic properties Testing'

Thesis (MA)--Stellenbosch University, 2003.
ENGLISH ABSTRACT: The aim of this study was to investigate the psychometric properties of a screening test of cognitive ability, the Paper and Pencil Games Level 2 (PPG Level 2), for Tigrignaspeaking schoolchildren in Eritrea. This study represents one of the first attempts to measure cognitive ability in Eritrea. The PPG was developed in South Africa (Claassen, 1996) as a group test of general cognitive ability for children in Grade 2 and 3 (PPG Level 2), and Grade 4 and 5 (PPG Level 3). The PPG provides Total, Verbal and Nonverbal ability scores. The Verbal Scale consists of two subtests, namely (a) Verbal and Quantitative Reasoning and (b) Comprehension. The Non-verbal Scale consists of three subtests, namely (a) Figure Classification, (b) Figure Series, and (c) Pattern Completion. Although the PPG has the appearance of a standardized intelligence test, Claassen emphasized that it is best used as a screen for academic difficulties or failures. Participants were 577 Tigrigria-speaking Grade 3 children. The children were selected from schools in the capital, Asmara, from small towns, and villages. Eleven schools participated. The participants can be considered representative of the Grade 3 Tigrignaspeaking population in Eritrea. The PPG Level 2 was completed under supervision of the researcher. Classical and Rasch item analyses were conducted on the Verbal and Non-verbal Scales, respectively. The internal consistency of the Non-verbal scale can be considered satisfactory for a screening instrument (Cronbach's a = .85). Furthermore, the non-verbal items showed satisfactory fit to the Rasch model (INFIT values and OUTFIT values < 1.3 for all items), suggesting that they measure a unidimensional construct. In addition, the item difficulty estimates corresponded well with the serial order of the items, with easy items being presented earlier than more difficult items. The internal consistency of the Verbal scale was lower (Cronbach's a = .72), which can probably be attributed to the relative easiness of the items for the particular group of participants. The verbal items also showed satisfactory fit to the Rasch model. The Rasch analysis, which expresses person ability and item difficulty on the same scale, clearly showed that the Verbal items were too easy for the majority of the children. However, it should be kept in mind that the PPG is intended to discriminate among children with low ability. Hence, the observed mismatch between the abilities and item difficulties was not unexpected. It should also be noted that the serial order of the items did not correspond well with item difficulty, with some difficult items being presented early and some easy items presented late in the scale. The five subtests of the PPG were subjected to a confirmatory factor analysis. Two models were specified and compared. Model 1 specified a single general factor; this provided a more parsimonious description of the data and showed a satisfactory fit with the data, though a bit weaker than that of Model 2. Model 2 specified two correlated factors, namely a Verbal and a Non-verbal factor. Model 2 also fitted the data well, but a high correlation between the factors was observed (r = .77; r2 = .59), suggesting the presence of a general factor. The results provide support for two levels of interpretation, namely on the Total score level and the Verbal and Non-verbal level. The validity of the PPG Level 2 was further investigated by examining the correlations between the PPG scores and teacher ratings of academic achievement. Because different schools had different raters, the correlations within each of the schools were pooled to obtain an estimate of the correlations between the PPG scales and academic achievement for the total group. The pooled correlation for the PPG Total score with academic achievement was .56, for the Non-Verbal score .53, and for the Verbal score .41. The correlations for the Total and Non-verbal scores are similar to those typically reported in the educational psychology literature and provide support for the validity of these scales as a screen for academic difficulties. The results show that the PPG, which was developed in South Africa, may be fruitfully exported to Eritrea. It is recommended, however, that before the PPG Level 2 is routinely used for screening purposes with Tigrigna-speaking children, the functioning of the Verbal Scale should be re-examined and possibly some of the Verbal items should be rewritten.
AFRIKAANSE OPSOMMING: Die doel van die onderhawige studie was om die psigometriese eienskappe van 'n siftingstoets van kognitiewe vermoë, naamlik die Paper and Pencil Games Level 2 (PPG Level 2), vir Tigrigna-sprekende kinders in Ertirea te bestudeer. Hierdie studie verteenwoordig een van die eerste pogings om kognitiewe vermoë in Eritrea te meet. Die PPG is in Suid-Afrika ontwikkel (Claassen, 1996) as 'n groeptoets van kognitiewe vermoë vir kinders in Grade 2 en 3 (PPG Level 2), en Grade 4 en 5 (PPG Level 3). Die PPG lewer tellings van kognitiewe vermoë op drie vlakke, naamlik Totaal, Verbaal en Nie-Verbaal. Die Verbale skaal bestaan uit twee subskale: (a) Verbale en Kwantitatiewe redenering en (b) Begrip. Die Nie-Verbale skaal bestaan uit drie subskale, naamlik (a) Figuur Klassifisering, (b) Figuurreekse en (c) Patroonvoltooiing. Alhoewel die PPG op die oog af soos 'n konvensionele intelligensietoets lyk, beklemtoon Claassen dat dit te beste geskik is as 'n siftingsinstrument vir akademiese probleme of mislukkings. Die deelnemers was 577 Tigrigna-sprekende kinders in Graad 3. Die kinders is uit skole van die hoofstad, Asmara, klein dorpe en geselekteer. Elf skole het aan die studie deelgeneem. Daar kan aanvaar word dat die deelnemers verteenwoordigend is van die Graad 3 Tigrigna-sprekende populasie in Eritrea. Die PPG Level 2 is onder supervisie van die navorser voltooi. Klassieke en Rasch item-ontledings is op die Verbale en Nie- Verbale skale, onderskeidelik, uitgevoer. Die interne konsekwentheid van die Nie- Verbale skaal kan as bevredigend vir 'n siftingsinstrument beskou word (Cronbach se a = .85). Hierbenewens het die Nie-Verbale items 'n bevredigende passing met die Rasch model getoon (INFIT gemiddelde kwadrate en OUTFIT gemiddelde kwadrate < 1.3 vir alle items), wat daarop dui dat die items 'n essensiëel eendimensionele konstruk meet. Die moeilikheidswaardes van die Nie- Verbale items het ook sterk ooreengestem met die volgorde waarin die items in die skaal aangebied word - die maklike items is eerste aangebied en daarna die moeilike items. Die interne konsekwentheid van die Verbale skaal was laer (Cronbach se a = .72). Die laer koëffisiënt kan waarskynlik aan die relatiewe lae moeilikheidsgraad van die Verbale items toegeskryf word. Die Verbale items het egter ook 'n bevredigende passing met die Rasch model getoon. Die Rasch ontleding, wat vermoë en item moeilikheid op dieselfde skaal uitdruk, het duidelik getoon dat die Verbale items te maklik vir die meeste kinders was. Daar dien egter op gelet te word dat die PPG ontwerp is om te diskrimineer tussen kinders met relatiewe lae vermoëns. In hierdie lig gesien is die swak passing tussen vermoë en item moeilikhede nie te onverwags nie. Die volgorde waarin die items in die skaal aangebied word het ook nie goed ooreengestem met die item moeilikheidswaardes nie - sommige moeilike items is vroeg in die skaal aangebied en sommige maklike items laat in die skaal. Die vyf subtoetse van die PPG is aan 'n bevestigende faktorontleding onderwerp. Twee modelle is gespesifiseer en vergelyk. Model 1 het 'n enkele algemene faktor gespesifisieer.

The measurement and monitoring of the elastic properties of cement-based materials is very important for assessing their quality, integrity and performance. Due to the nonhomogeneous and time-dependent characteristics of these materials, it is difficult to observe the developments in elastic properties with traditional destructive methods. The aim of this thesis is to determine and monitor elastic properties of mortar specimens made with different cements by using resonant frequency and ultrasonic pulse velocity test methods, and to obtain relationships between these elastic properties. For this purpose, eight different cement mortar mixtures were prepared with different constituent CEM I cements. Dynamic elastic moduli, static elastic moduli, dynamic Poisson&rsquo
s ratio and strength of these mixtures were observed for different ages. The relationships between these elastic properties are determined and the results obtained from two different nondestructive test methods are compared. Although nondestructive tests made it possible to obtain elastic properties of mortar mixtures, the results revealed that it is very difficult to develop a single relationship between different elastic properties of mortars with varying mixture proportions. This situation is mainly due to the anisotropy and nonlinear behavior of the mortar and the difficulty of describing the actual behavior of mortar by formulations defined for perfectly elastic materials.

Le comportement mécanique de films minces métalliques déposés sur des substrats souples joue un rôle déterminant dans les performances de l'électronique flexible et des micro- systèmes électromécaniques (MEMS).Dans un premier temps, une nouvelle méthode est présentée pour caractériser le module d'élasticité de films minces submicroniques. Avec deux couches déposées de chaque côté et sur la moitié du substrat polymère, la corrélation d'image numérique (CIN) a été utilisée pour mesurer simultanément la déformation du film et du substrat in situ au cours d'un essai de traction. La différence entre les déformations mesurées sur la partie vierge et le composite permet d'extraire les propriétés élastiques de films minces de manière simple et avec grande précision. Comme attendu, la distribution des déformations est uniforme au travers de l'épaisseur du film ce qui indique une adhésion parfaite entre le film et le substrat. Dans le cas de films minces de tungstène, de chrome, de nickel et de cuivre, les valeurs de module obtenues sont proches de celles des mêmes matériaux à l'état massif.Dans un deuxième temps, une nouvelle méthode expérimentale utilisant une machine de déformation uniaxiale est présentée pour étudier l'effet Bauschinger dans des films minces métalliques déposés sur des substrats étirables. Grâce à un dispositif original, les films minces sont déposés sur des substrats prétendus et peuvent donc être déformés alternativement en tension et en compression dans un large domaine de déformations. La déformation élastique intra granulaire des films minces polycristallins et la déformation macroscopique du substrat sont mesurées in situ par diffraction des rayons X et CIN respectivement. A partir des courbes « déformation élastique – déformation macroscopique », la réponse mécanique de l'ensemble film / substrat est analysée au vu de l'histoire complète du chargement et de la microstructure (contraintes résiduelles, texture) des films minces
The mechanical behavior of metallic thin films deposited on soft substrates plays a crucial role in the performance of flexible electronics and MicroElectroMechanical Systems (MEMS).At first, a novel method is presented to characterize the in-plane elastic modulus of sub micrometer thin films. With two coating layers bonded symmetrically to half polyimide substrates, Digital Image Correlation (DIC) has been employed to measure time-resolved full-field strain maps of film and substrate during in situ tensile testing. The strain differences between virgin and composite parts allowed to extract the elastic properties of the thin films in a simple way with high precision. As expected, the strain distribution is uniform through the film thickness which indicates a perfect adhesion between the film and the substrate. In the case of tungsten, chromium, nickel and copper films, the values obtained are close to the bulk one.In a second step, a new experimental method using uniaxial tensile testing is presented to study Bauschinger effect in thin metallic films deposited on stretchable substrates. Thanks to our new pre-tensile setup (specific grips), the thin films were deposited on pre-stretched substrates and thus could be deformed alternately in tension and compression within a large strain domain. The elastic intra-granular strain of polycrystalline thin films and true strain of substrates are measured in situ by X-Ray Diffraction (XRD) and DIC. From lattice strain-true strain curves, the mechanical response of copper and nickel /substrate sets is analyzed in view of the complete loading history and the presence of residual stresses and crystallographic texture in thin films

The work is divided into two parts. The practical part deals with the testing properties of soils which are using in new road in Nové Město na Moravě and the testing of recycled materials which could replace this soils from road. The aim this part is to obtain values of elastic modulus which are then inserted into the computational model. In the second part of work the track road is modeled in the software which uses the Finite Element Method to calculate and respect physical properties of different materials and a load. The result of work will be studies with comparison of displacement and stress generated to using existing soils and recycled materials.

L’objectif de ce travail est d’étudier les couplages entre les propriétés hygroélastiques des papierset leur microstructure. L’exploitation d’images de papiers modèles acquises par microtomographieà rayons X a permis de caractériser de manière inédite l’évolution des propriétésmicrostructurales de ces matériaux en fonction de leurs conditions d’élaboration ainsique lors d’essais où ils ont été placés sous atmosphère à humidité relative contrôlée.Ces résultats constituent un apport nouveau pour la connaissance de la nature statistique desdescripteurs des propriétés des fibres (dimensions et orientation) et de leurs contacts (surface,degré de liaison), de l’architecture des réseaux fibreux que forment les papiers (nombrede contacts entre fibre) et pour la taille des volumes élémentaires représentatifs des propriétésmicrostructurales et élastiques de ces milieux. Sur la base de ces informations, différentsmodèles, plus oumoins raffinés, ont été élaborés dans le cadre de la théorie de l’homogénéisationdes structures périodiques discrètes, pour décrire les propriétésmécaniques des papiers.Cette approche apporte un éclairage nouveau sur le rôle des liaisons entre fibres sur leur comportement mécanique
The objective of this work is to study the coupling between the hygroelastic properties ofpapers and their microstructure. The use of images of models acquired by X-ray microtomographypapers allowed the characterization in an unprecedentedmanner of the evolutionofmicrostructural properties of thesematerials according to their production conditions andduring tests where they were placed in atmosphere at controlled relative humidity. These resultsprovide a new contribution to the knowledge of the statistical nature of the descriptorsof fibre properties (size and orientation) and their contacts (surface, bonding degree ratio), ofthe architecture of fibrous networks that papers constitute (number of fibre-to-fibre bonds)as well as of the size of the representative elementary volumes of microstructural and elasticproperties. Based on this information, various models, more or less sophisticated, were developedin the framework of the theory of homogenisation of discrete periodic structures todescribe the mechanical properties of paper. This approach sheds new light on the role offibre-to-fibre bonds on themechanical behaviour of thesematerials

For evaluation and quality control of concrete structures, the impact resonant frequency method is widely accepted for monitoring structure in-service properties and detecting structural damage. Common defects in concrete include consolidation problems during casting and development of micro-cracks during stages of hydration. Monitoring the dynamic characteristics of concrete plays an essential role in detecting real-time and early stages of deterioration. Ample research is focused on detecting large defects, however not much information is available on detection of minor defects of composites like fiber reinforced concrete. Change of elastic behavior when Polypropylene fibers are added as reinforcement is investigated. Destructive tests on structures in-service are not always feasible thus leaving non-destructive condition assessment as the only option. Amongst the various non-destructive tests available, vibrational tests provide a practical method to predict the dynamic moduli of structures (dynamic modulus of elasticity, dynamic modulus of rigidity and dynamic Poisson’s ratio). The objective of this research is to assess the dynamic elastic properties of Polypropylene Fiber Reinforced Concrete (PFRC) in correlation with induced cracks and common consolidation defects using a lab developed non-destructive testing method that relies on impulse excitation and stress wave propagation to measure changes in the resonant frequency when polypropylene fibers are added to concrete. In the experimental program, two fiber sizes, macro and micro, with various volume contents have been used for casting PFRC cylinders and prisms. Fundamental resonant frequencies were measured for all cylinders and prisms in the transverse and longitudinal directions. All measured frequencies are directly related to the low-strain dynamic modulus of elasticity. In addition, PFRC prisms were used to investigate the relationship between the dynamic modulus of elasticity and modulus of rigidity. Several batches of similar mixtures are used to investigate different parameters that affect the resonant frequency of concrete such as the water to cement ratio, curing condition and age. Results indicated a decrease in the resonant frequency and elastic properties with an increase of the fiber content or length. Micro fibers showed higher dynamic elastic moduli when compared to macro fibers of the same mixture under saturated curing conditions. Post-cracked PFRC cylinders and flexural fractured prisms retained some of the resonant frequency with macro fibers exhibiting better elastic recovery when cracked.
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