Improvement of algorithm for numerical crack modelling

For numerical simulation of crack modelling in fracture mechanics the eXtended finite element method (Xfem) has been recently accepted as a new powerful and efficiency methodology. In the paper we present the details of implementation of the Xfem algorithm in our in-house finite elements based software. Also, in this study, we investigated the impact of the node enrichment variations on results of the developed numerical procedure. In this study, objective was to examine the properties of standard Xfem algorithm without using of Near Tip enriching functions in order to create possibilities for future application Xfem in the zone of plasticity. In order to evaluate the computational accuracy, numerical results for the Stress Intensity Factors are compared with both theoretical and conventional finite element data. Obtained numerical results have shown a good agreement with the benchmark solutions. For calculation of the Stress Intensity Factors (SIF), we used the J-Equivalent Domain Integral (J-EDI) Method. Computational geometry issues, associated with the representation of the crack and the enrichment of the finite element approximation, are discussed in detail

The effect of shielding gas on the toughness of ALMg4.5Mn weld metals made by GMAW

The effect of MIG/MAG shielding gas on the toughness of aluminium alloy AlMg4.5Mn weld metal has been analysed using the instrumented Charpy pendulum for standard toughness testing. The MIG/MAG welding was performed in the shielded atmosphere of Ar, as well as the mixtures of gases Ar + 0.0307 % O 2, Ar + 30 % He + 0.0317 %O 2 and Ar + 48 % He + 0.0290 % O 2. Metallographic tests have been performed in order to check the appearance and porosity of the weld metal, as well as its toughness testing at different temperatures (20, - 90, - 196 °C), using the instrumental Charpy pendulum, in order to separate the crack initiation and crack growth energy. In this way, a comprehensive insight of the effect of shielding gas on the weld metal toughness has been obtained

Does the presence of an unerupted lower third molar influence the risk of mandibular angle and condylar fractures?

It has been suggested that unerupted lower third molars (M3) increase the fragility of the mandibular angle and simultaneously decrease the risk of condylar fracture. However, it is unknown whether this applies regardless of the direction and point of impact of the traumatic force. The aim of this study was to investigate the impact of an unerupted M3 on the fragility of the angle and condyle in terms of a force acting from different directions and affecting different regions of the mandible. Computed tomography scans of a human mandible and finite element methodology were used to obtain two three-dimensional models: a model with, and the other without an unerupted M3. A force of 2000 N was applied to three different regions of the models: the symphysis, ipsilateral body, and contralateral body, respectively. When the force was applied to the mandibular body, the results revealed increased angle fragility in cases with unerupted M3. When the force was applied to the symphysis, the condyle region showed higher fragility, irrespective of the presence of an unerupted M3. In summary, fragility of the angle and condyle regions depends on the presence of an unerupted M3 and on the direction and point of impact of the force

Effect of fillers and lubricants on acetylsalicylic acid release kinetics from Eudragit matrix tablets

The effect of fillers and lubricants on the dissolution rate of acetylsalicylic acid (ASA) from matrix tablets has been evaluated. Eudragit S-100 and Eudragit L-100-55 where chosen as matrix substances. The process of drug release in vitro was studied by the modified half-change method. The dissolution data were evaluated on the basis of theoretical dissolution equations and by linear transformation of dissolution curves. Differences in release rate of ASA from matrix tablets, regarding the diluents used, appeared to be more significant when matrices contained Eudragit L-100-55 as compared to Eudragit S-100. The highest dissolution rates of ASA were observed in the presence of Lubritab as lubricant. The other lubricants used showed similar effects on the release rate of ASA. The release of ASA from samples containing Eudragit L-100-55 corresponded best to the zero-order kinetics. The best-fitted model for the ASA release from tablets prepared with Eudragit S-100 was obtained by using the Hixson-Crowell equation

Third-order derivative UV spectrophotometry and densitometry for the simultaneous assay of acetylsalicylic acid and salicylic acid in tablet formulations

Third-order derivative spectrophotometry is proposed for simultaneous determination of acetylsalicylic acid and free salicylic acid in sustained-release tablets, and compared with TLC-densitometry. Both methods were evaluated through selectivity, and accuracy tests. Results for acetylsalicylic acid and salicylic acid in aspirin sustained-release tablets showed good agreement