Search results for "Cracking"
showing 10 items of 102 documents
Optimal die Design for Cold Extrusion Processes
1999
The design of cold extrusion processes requires the optimisation of several process variables in order to obtain a defect free product. The fulfilment of different objectives, such as the minimisation of forming loads or the homogeneity of the deformations, is highly requested. Nevertheless, several other relevant aspects of extrusion processes have to be taken into account and require a suitable optimisation of the process parameters and in particular of the die shape. In this paper, tool life has been assumed as the most relevant goal and an effective die design procedure as been setup. It is well known that fatigue cracking of the dies is the principal cause of dies failure in cold extru…
Influence of the U3O7 domain structure on cracking during the oxidation of UO2
2010
Abstract Cracking is observed when a UO 2 single crystal is oxidised in air. Previous studies led to the hypothesis that cracking occurs once a critical depth of U 3 O 7 oxidised layer is reached. We present some μ-Laue X-ray diffraction results, which evidence that the U 3 O 7 layer, grown by topotaxy on UO 2 , is made of domains with different crystalline orientations. This observation was used to perform a modelling of oxidation coupling chemical and mechanical parameters, which showed that the domain patterning induces stress localisation. This result is discussed in comparison with stress localisation observed in thin layer deposited on a substrate and used to propose an interpretation…
Cracking Activity and Hydrothermal Stability of MCM-41 and Its Comparison with Amorphous Silica-Alumina and a USY Zeolite
1996
It has been found that the cracking activity of MCM-41 for a reaction catalyzed by strong acids site, such asn-heptane cracking, is much lower than that of a USY zeolite, and similar to that of amorphous silica-alumina. The higher activity of USY is due to the presence of stronger Bronsted acid sites in the zeolite. In the case of gas oil cracking, the greater accessibility of the large molecules to acid sites in MCM-41 relative to USY makes the difference in activity between these two catalysts much smaller than for the pure hydrocarbon. In the calcined state MCM-41 is more active and gives more gasoline and less gases and coke than amorphous silica-alumina. However, when the catalysts wer…
Mechanical Behavior of Concrete Columns Confined by Laterally Pre-Tensioned FRP
2011
This paper presents the results of an experimental investigation of concrete columns confined by a wound pre-tensioned carbon filament yarn. Yarn winding equipment was developed in the Institute of Polymer Mechanics with the ability to set the desired pre-tension force and thereby producing confined concrete specimens with different initial lateral pressure. It is shown that initial lateral pressure increases the axial stress at which intense internal cracking of the concrete develops.
Influence of the process variables on the product distribution and catalyst decay during cracking of paraffins
1986
Abstract The influence of the partial pressure of the hydrocarbon, reaction temperature, time on stream and the presence of olefins on the product distribution and the kinetics and decay during the cracking of n-heptane on an REHY zeolite were studied. It was found that the isomerization to cracking ratio depends on the hydrocarbon partial pressure. The active sites for cracking and isomerization are not the same and those for cracking decay faster, the selectivity changing with the degree of decay of the zeolite. The protolytic to β-cracking ratio, and therefore the paraffin to olefin ratio, are a function of the partial pressure of n-heptane. Both reactants and products have a marked infl…
Performance-based characterization of recycled polymer modified asphalt mixture
2021
Due to the introduction of secondary materials, the asphalt mixtures to be designed and tested in our laboratories are constantly becoming much more complex than traditional asphalt mixtures making difficult to use conventional laboratory procedure and/or predict expected results. This study proposes a comprehensive characterization of asphalt mixture modified with recycled polymer compound by using both wet and dry process proposing adjustments to laboratory mixing and sample compaction procedure. Accordingly, three AC20 Hot Asphalt Mixture (HMA) were designed and their conventional and performance related properties were assessed by looking at a) Indirect Tensile test (ITS) a) moisture da…
The influence of branching isomerization on the product distribution obtained during cracking of n-heptane on acidic zeolites
1985
Abstract The initial selectivities for the primary products occurring during the cracking of n-heptane on a rare-earth (RE)-HY ultrastable zeolite up to 470°C have been calculated. The activation energies for the cracking of n-heptane and its branched isomers in the fraction C4 + C3 have been obtained by molecular orbital calculations, and these values and the predicted product distribution have been compared with those obtained experimentally. It is concluded that the cracking of n-heptane on large-pore zeolites may take place by different parallel routes involving protolytic and β-cracking of n-heptane and β-cracking of the readily formed branched carbenium ions. The relative importance o…
Steel Fibres: Effective Way to Prevent Failure of the Concrete Bonded with FRP Sheets
2016
Although the efficiency of steel fibres for improving mechanical properties (cracking resistance and failure toughness) of the concrete has been broadly discussed in the literature, the number of studies dedicated to the fibre effect on structural behaviour of the externally bonded elements is limited. This experimental study investigates the influence of steel fibres on the failure character of concrete elements strengthened with external carbon fibre reinforced polymer sheets. The elements were subjected to different loading conditions. The test data of four ties and eight beams are presented. Different materials were used for the internal bar reinforcement: in addition to the conventiona…
Analysis of thin film cracking and buckling on compliant substrate by fragmentation test
2007
Application of coating fragmentation test for determination of coating properties is considered. A probabilistic model of coating fragmentation under uniaxial tensile loading is applied for coating and interface property identification of thin brittle coating/polymer substrate system. A finite element model is developed to simulate the process of buckle formation in coating strips during fragmentation test. The measured buckle geometry parameters and buckle density evolution as a function of the applied strain is used to estimate the interface toughness.
Error analysis and calibration for a novel pipe profiling tool
2020
Integrity of industrial pipework is ensured through routine inspection. Internal visual inspection tools are capable of characterising degradation in the form of corrosion, pitting, erosion and cracking. The accuracy of such inspection systems has a direct impact on decisions regarding the remaining lifetime of the asset. By minimising error margins, the asset may be operated with confidence for longer, with less uncertainty. This paper considers a probe system consisting of a laser profiler and camera that produces a textured 3D model of the internals of 2 – 6 inch pipework. The accuracy of the system is defined by the ability to extract laser projections from an image as it travels down t…