Search results for "Crack"
showing 10 items of 209 documents
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…
A nonlinear finite element approach with cohesive-frictional interfaces for mode II Transverse Crak Tension test insight
2016
In many circumstances structural failure modes are driven by the formation and propagation of fractures. For instance in composite laminate structures one of the most worrying condition is delamination, which is an interlaminar progressive fracture. Fracture toughness is the material mechanical parameters which ensure fracture safe condition and it is also an essential parameter for performing nonlinear structural analysis, no matter if based on Fracture Mechanics or by means of Interface Cohesive theories. It is then of paramount relevance to evaluate the critical fracture energy by means of simple and reliable laboratory tests. Several tests are available for the direct determination of m…
Strain localization and fracture in isotropic damaging materials: a novel augmented-finite element strategy
2022
On relation between J-integral and heat energy dissipation at the crack tip in stainless steel specimens
2019
In this paper, an experimental procedure to evaluate the elastic-plastic J-integral at the tip of a fatigue crack is presented. According to this new approach, the elastic component of the J-integral is derived from Thermoelastic Stress Analysis, while the plastic component of the J-integral is derived from the heat energy loss. An analytical link is proposed to apply this new experimental technique. Therefore, the elastic-plastic J-integral range was evaluated starting from infrared temperature maps measured in situ during crack propagation tests of AISI 304L stainless steel specimens. It was found that the range of the infrared thermography-based J-integral correlated well the crack growt…
Fatigue Design of Cruciform Joints including V-notch Effect at the Weld Toe
2014
Abstract The present paper proposes a new and more accurate fatigue life prediction model for fillet welded joints in steel subjected to constant amplitude loading. With the traditional fracture mechanics approach, the greatest difficulty when computing the fatigue life of a welded detail is to determine the initial crack size a0. The classical way to determine the stress intensity factor K (SIF) is by using the following formula Where σ is the applied stress, a is the crack size and g(a/T) the geometrical correction factor which has been determined by Gurney function or similar solutions. This approach is not accurate for short crack because of the singular V-notch behaviour close to the c…
Experimental characterization of micromechanical and microphological properties of nickel base alloys strained by the growth of an ovide payer made i…
2011
The loss of the corrosion resistance of the alloy 600, a nickel base alloy, during the oxidation in pressurized water reactor (PWR) has been demonstrated by many studies. It induces the intergranular stress corrosion cracking (IGSCC). If the chemical composition and the structure of the growing oxide are well-known, the mechanical influence of the oxide on the alloy has not been fully studied, yet. This study aims at bringing new knowledge of the oxidation impact on the mechanical response of the alloy. A new methodology is introduced for determining the local nanodeformation of the alloy 600 induced either by an oxidation or by a tensile loading. This method is based on nanodots disposed a…
Strain field measurements in polycrystalline tantalum
2013
National audience; The unterstanding and the local quantification of surface strain distribution is a key element of crack initiation analysis. Experiments following up the local strain distribution have been carried out, based on the construction of several hundred micrometers wide strain maps ; and using gratings of regularly spaced micrometric markers deposited by lithography. The strain maps are computed using a specific routine, allowing to quantify the local strain distribution at the grain scale for different interrupted tensile loads.