Search results for "Cracking"

Catalytic activity of large-pore high Si/Al zeolites: Cracking of heptane on H-Beta and dealuminated HY zeolites

1987

Abstract The catalytic activity, selectivity, catalyst decay, thermal and hydrothermal stability, and acidity of H-Beta and HY zeolites with Si Al ratios of 7.5 and 10, respectively, have been studied during cracking of n-heptane at 450 °C and atmospheric pressure. It has been found that the H-Beta zeolite is more active and decays more slowly than HY. H-Beta presents a higher steric hindrance for dibranched molecules and therefore its open structure should be smaller than that of HY. A lower hydrogen transfer activity and hydrothermal stability is observed for H-Beta in comparison with the corresponding HY.

Relationship between radial and concentric cracking of tomato fruit

1983

Abstract A study with 62 genotypes was carried out to establish correlations existing between the percentages of fruits showing concentric cracks of more or less than 2 cm and radial cracks of more or less than 2 cm, considering both early and total production. Over a determined productive period, the susceptibility to form large or small cracks was controlled by the same genetic system (rG = 0.89 – 0.95), yet there was a genetic difference between susceptibility to radial and concentric cracking (rG = 0.53 – 0.68). Genetic systems for susceptibility to radial and concentric cracking seemed to show similarly over the first harvesting and over the total productive period ( r G ⋍ 1 ). Environ…

Soil structure and bypass flwo processes in a Vertsol under sprinkler and drip irrigation.

2007

In this paper morphological and physical characteristics, as well as flow behaviour of a Mediterranean Vertisol under the influence of two different irrigation systems currently used for irrigation, i.e. drip and sprinkler systems, were compared. No differences in soil texture, compaction and in potential cracking were found on cores from the two fields. However, field application of methylene blue showed the presence of continuous macropores, penetrating up to depths of 20-25 cm from the soil surface, in the field where the drip system was in use (field 1). This was considered to be the pre-existing soil structure. Instead, macropores terminating at a depth ranging between 5 and 10 cm from…

A novel micro-mechanical model for polycrystalline inter-granular and trans-granular fracture

2017

In this work, a novel grain boundary formulation for inter-and trans-granular cracking of polycrystalline materials is presented. The formulation is based on the use of boundary integral equations for anisotropic solids and has the advantage of expressing the considered problem in terms of grain boundary variables only. Inter-granular cracking occurs at the grain boundaries whereas trans-granular cracking is assumed to take place along specific cleavage planes, whose orientation depends on the crystallographic orientation of the grains. The evolution of inter-and trans-granular cracks is then governed by suitably defined cohesive laws, whose parameters characterize the behavior of the two f…

Theta-1 zeolite catalyst for increasing the yield of propene when cracking olefins and its potential integration with an olefin metathesis unit

2017

[EN] There is a need for on-purpose propene production technologies beyond energy-intensive steam cracking. Hexene is a compound with limited value that can be found in several streams in the refinery and can readily crack on zeolites at lower temperatures and shorter contact times than those used for cracking alkanes. Cracking over ZSM-5 zeolite yields high selectivity to light olefins. These results are improved by Theta-1 zeolite, which can yield a remarkable propene molar selectivity of 180% (90 wt%) at 90% conversion, close to the maximum thermodynamic yield. Moreover, crystal engineering allowed its TOF to increase by more than 50%. Based on these results we also identified some prosp…

Elucidating the Effect of Bimodal Grain Size Distribution on Plasticity and Fracture Behavior of Polycrystalline Materials

2020

The refinement of grains in a polycrystalline material leads to an increase in strength but as a counterpart to a decrease in elongation to fracture. Different routes are proposed in the literature to try to overpass this strength-ductility dilemma, based on the combination of grains with highly contrasted sizes. In the simplest concept, coarse grains are used to provide relaxation locations for the highly stressed fine grains. In this work, a model bimodal polycrystalline system with a single coarse grain embedded in a matrix of fine grains is considered. Numerical full-field micro-mechanical analyses are performed to characterize the impact of this coarse grain on the stress-strain const…

2019

Abstract The fatigue life of thermally sprayed Al2O3- and Cr2O3-based coatings has been studied under low-energy (0.7–5 mJ) impact conditions. A threshold impact energy and amount of repetitions the coatings can endure with said energy before catastrophic failure was obtained. The catastrophic failure was determined to occur when the fracture mode of the coating switched from brittle cone cracking to quasi-plastic radial cracking. The results are examined relative to the microstructural features along with other properties of the coatings - hardness and cavitation resistance. The experiment provided a new approach for a straightforward comparison of the micro-scale impact fatigue life of th…

The effects of laboratory ageing on rheological and fracture characteristics of different rubberised bitumens

2018

Ageing of bituminous materials can result in loss of the durability of a flexible pavement. Using rubberised bitumens can enhance pavement performance while at the same time it solves a serious waste disposal problem. Combining Warm Mix Asphalt (WMA) additives with rubberised bitumens reduces the difficulties associated with the production of asphalt mixtures using this modified binder. This work was conducted to study the effect of ageing using fundamental parameters based on performance, i.e., CTOD and Glover-Rowe parameters have been related to pavement cracking. Different unmodified bitumens and rubberised bitumens were short-term aged using the Thin Film Oven Test (TFOT) and long- term…

A simple model for the calculation of the axial load-carrying capacity of corroded RC columns

2015

In the present paper, a simplified model is used to determine the axial load-carrying capacity of compressed short reinforced concrete columns subjected to corrosion processes. The model considers members with circular and square cross-sections and accounts for—cover spalling, —concrete core confinement induced by transverse steel reinforcement, —buckling of longitudinal reinforcing bars. Strength reduction in concrete cover and core due to cracking induced by rust formation, reduction of steel area in longitudinal bars and transverse stirrups due to general and pitting corrosion and loss of confinement pressure are considered. The load-carrying capacity and load-axial strain curves here ge…

Thermo-rheological analysis of WMA-additive modified binders

2020

AbstractThermo-rheological characteristics of unmodified and modified bitumen have significant impacts on the mechanical response of asphalt. This study investigates the impacts of an organic and a chemical Warm Mix Asphalt additive on bitumen thermo-rheological and mechanical characteristics. Modified binders with different concentrations of each additive were studied and analysed comparatively to a 40/60 penetration grade bitumen. Frequency sweep tests were performed at different ageing levels to characterise the Linear Viscoelastic properties. The multiple stress creep and recovery, linear amplitude sweep (LAS) and low temperature creep stiffness tests, together with the Glover–Rowe (G–R…