Fracture properties and mechanisms

Fracture Properties and Mechanisms of Polyamide/Clay Nanocomposites... 

Fracture Properties and Mechanisms of Polyamide/Clay NanocompositesOn the Toughness of Nanomodified Polymers and Their Traditional Polymer Composites... 

Gershon B. and Marom G. (1975). Fracture toughness and mechanical properties of glass fiber-epoxy composites. J. Mater. Sci. 10, 1549-1556. 

Low, I.M. and Mai, Y.W. (1990). Fracture properties and failure mechanisms of pure and toughened epoxy resins. In Handbook of Ceramics (N.P. Cheremisinoff ed.), Marcel Dekker, New York, pp. 105-160. 

Given the existence of interphases and the multiplicity of components and reactions that interact to form it, a predictive model for a priori prediction of composition, size, structure or behavior is not possible at this time except for the simplest of systems. An in-situ probe that can interogate the interphase and provide spatial chemical and morphological information does not exist. Interfacial static mechanical properties, fracture properties and environmental resistance have been shown to be grealy affected by the interphase. Careful analytical interfacial investigations will be required to quantify the interphase structure. With the proper amount of information, progress may be made to advance the ability to design composite materials in which the interphase can be considered as a material variable so that the proper relationship between composite components will be modified to include the interphase as well as the fiber and matrix (Fig. 26). 

Abstract The fracture properties and microdeformation behaviour and their correlation with structure in commercial bulk polyolefins are reviewed. Emphasis is on crack-tip deformation mechanisms and on regimes of direct practical interest, namely slow crack growth in polyethylene and high-speed ductile-brittle transitions in isotactic polypropylene. Recent fracture studies of reaction-bonded interfaces are also briefly considered, these representing promising model systems for the investigation of the relationship between the fundamental mechanisms of crack-tip deformation and fracture and molecular structure. 

Methods of objective measurement of cereal foam structures are reviewed, including image analysis, confocal microscopy and x-ray tomography. The analysis of foam structures and their relationship with mechanical and rheological properties is described, and also the relationships between these structures and sensory descriptors such as crispness, crunchiness and texture. The size, shape and anisotropy of bubbles and their cell walls in foams are seen as critical in determining their fracture properties and sensory perception of crispness. Techniques for measuring crispness using acoustic emission and force-deformation profiles are discussed. 

The task for the DECOVALEX research teams was to predict the THM effects in the buffer material inside the test pit and in the surrounding rock, both during excavation of the test pit and the heater testing. The test case was divided into three main tasks Tasks 2A, 2B. and 2C. Task 2A was to predict the HM effects in the rock cau,sed by the excavation of the test pit. Geometrical, mechanical and hydraulic rock properties, as well as hydraulic conditions before excavation, were given to the research teams, and they were asked to predict water inflow distribution in the test pit. Task 2B was a model calibration of rock and fracture properties and the hydromechanical boundary conditions, based on actual measured results predicted in Task 2A. Task 2C was to predict the THM effects in the rock and buffer during the heating experiment. The rock model was presumed to have properties based on the calibration in Task 2B. with the calibrated permeability distribution in the near-field rock. At... 

An extensive examination of the fracture network and mechanical data has been undertaken to determine models of the fracture characteristics of the three formations, the uncertainties in the parameterisation of the models, and the sensitivity of the upscaled flow properties to the underlying parameter variations. The methodology used to calculate effective hydraulic conductivity values and their sensitivity to the small-scale model is described in Blum el al. (2003). The study undertaken to obtain the effective hydraulic conductivity under different stress conditions and presented in Blum et al. (2003) revealed that the important parameters in modelling HM processes in the fractured rock mass are the fracture density, the mechanical (M) properties and the M property variations through the rock mass. 

The most widely studied polymer blends of PLA are those containing polyc-aprolactone (PCL). PCL is also degradable polyester and due to its low Tg it exhibits rubbery characteristics with an elongation at break of approximately 600 %, which makes it an ideal candidate for toughening PLA. However, immiscibility of PLA and PCL in binary blends, courses phase separation, and tends to lower the fracture properties and in generally lead to insignificant improvements in mechanical properties. Due to this drawback, current researches... 

Hristov V. N. Krumova M. Vasileva St. Michler G.H. Modified polypropylene wood flour composites. Fracture deformation and mechanical properties. Journal of Applied Polymer Science, vol.92, No.2, (2004), pp. 1286-1292... 

OlHar Harismendy, L, del Rio, M., Marieta, C., Gavalda, J., Mondragon, I. Dicyanate ester-po-lyetherimide semi-interpenetrating polymer networks. II. Effects of morphology on the fracture toughness and mechanical properties. J. Appl. Polym. Sci. 80 (2001) 2759-2767. 

Du AH, Peng ZL, Zhang Y, Zhang YX (2004) Fracture morphology and mechanical properties of ethylene/vinyl acetate rubber vulcanizates reinforced by in situ prepared sodium methacrylate. J Polym Sci B 42(9) 1715-1724... 

The fracture behaviour and mechanical properties of the composites are generally influenced by the interfacial structure or the fibre/matrix interactions. The nonlinear behaviour in the L-D curve and the pull-out of the fibre from the matrix without plastic deformation have demonstrated experimentally that the weak bonding between the fibres and by the van der Waals force allows the shear sliding deformation at tiie interface. The weak interaction between the... 

The effect of the PU molecular induced structural order on the physical properties and mechanical performance of PU was analysed. The polyaddition conditions and the modification of the structural order when inducing different specific distributions of the hard segments on the increasing macromolecular chain, were investigated in terms of PU deformation and fracture behaviour. 

It is very important, from one hand, to accept a hypothesis about the material fracture properties before physical model building because general view of TF is going to change depending on mechanical model (brittle, elasto-plastic, visco-elasto-plastic, ete.) of the material. From the other hand, it is necessary to keep in mind that the material response to loads or actions is different depending on the accepted mechanical model because rheological properties of the material determine type of response in time. The most remarkable difference can be observed between brittle materials and materials with explicit plastic properties. 

Information supplied by flaw visualization systems has decisive influence on fracture assessment of the defect. Results of expert ultrasonic examination show that in order to take advantage of AUGUR4.2 potentialities in full measure advanced methods of defect assessment should be applied using computer modelling, in-site data of material mechanical properties and load monitoring [4]. 

The Institute has many-year experience of investigations and developments in the field of NDT. These are, mainly, developments which allowed creation of a series of eddy current flaw detectors for various applications. The Institute has traditionally studied the physico-mechanical properties of materials, their stressed-strained state, fracture mechanics and developed on this basis the procedures and instruments which measure the properties and predict the behaviour of materials. Quite important are also developments of technologies and equipment for control of thickness and adhesion of thin protective coatings on various bases, corrosion control of underground pipelines by indirect method, acoustic emission control of hydrogen and corrosion cracking in structural materials, etc. 

Finally, the nature of the crystalline microstmcture, ie, crystal size and morphology and the textural relationship among the crystals and glass, is the key to many mechanical and optical properties, including transparency/opacity, strength and fracture toughness, and machinabiUty. These microstmctures can be quite complex and often are distinct from conventional ceramic microstmctures (6). 

The tetrahedral network can be considered the idealized stmcture of vitreous siUca. Disorder is present but the basic bonding scheme is still intact. An additional level of disorder occurs because the atomic arrangement can deviate from the hiUy bonded, stoichiometric form through the introduction of intrinsic (stmctural) defects and impurities. These perturbations in the stmcture have significant effects on many of the physical properties. A key concern is whether any of these defects breaks the Si—O bonds that hold the tetrahedral network together. Fracturing these links produces a less viscous stmcture which can respond more readily to thermal and mechanical changes. 

In addition to chemical analysis a number of physical and mechanical properties are employed to determine cemented carbide quaUty. Standard test methods employed by the iadustry for abrasive wear resistance, apparent grain size, apparent porosity, coercive force, compressive strength, density, fracture toughness, hardness, linear thermal expansion, magnetic permeabiUty, microstmcture, Poisson s ratio, transverse mpture strength, and Young s modulus are set forth by ASTM/ANSI and the ISO. 

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