Effect of defect size on P-S-N curves in Very-High-Cycle Fatigue

It is well-known that internal defects play a key role in the Very-High-Cycle Fatigue (VHCF) response of metallic materials. VHCF failures generally nucleate from internal defects, whose size strongly affects the material strength and life. Therefore, S-N curves in the VHCF regime are defect size dependent and the scatter of fatigue data is significantly influenced by the statistical distribution of the defect size within the material. The present paper proposes an innovative approach for the statistical modeling of Probabilistic-S-N (P-S-N) curves in the VHCF regime. The proposed model considers conditional P-S-N curves that depend on a specific value of the initial defect size. From the statistical distribution of the initial defect size, marginal P-S-N curves are estimated and the effect of the risk-volume on the VHCF response is also modeled. Finally, the paper reports a numerical example that quantitatively illustrates the concepts of conditional and marginal P-S-N curves and that shows the effect of the risk-volume on the VHCF response

Microstructure and preliminary fatigue analysis on AlSi10Mg samples manufactured by SLM

Nowadays, selective laser melting (SLM) is considered as the most challenging technology for manufacturing complex components in different industrial fields, such as biomedical, aerospace and racing. It is well-known that SLM may yield to microstructures significantly different from those obtained by conventional casting, thus affecting the mechanical properties of the component. In the present paper, microstructural and mechanical tests were carried out on AlSi10Mg samples manufactured by SLM technique in the XY building configuration. Homogeneous composition and typical microstructures were achieved for all the investigated samples. The mechanical properties were assessed through a tensile test and through the Impulse Excitation Technique (IET). The feasibility of ultrasonic Very High Cycle Fatigue (VHCF) tests with Gaussian specimens characterized by large loaded volumes (risk-volumes) was also experimentally verified in the paper. A Gaussian specimen was designed and manufactured. A preliminary ultrasonic test was then carried out on the manufactured specimen and the fracture surface was finally investigated

CARATTERIZZAZIONE A FATICA AD ALTISSIMO NUMERO DI CICLI DI UN ACCIAIO AISI H13 AD ELEVATO GRADO DI PUREZZA

Experimental results recently obtained by testing high-strength steels at a very high number of cycles showed that failures could occur at stress amplitudes below the conventional fatigue limit with nucleation of cracks from defects or inclusions inside the material. Therefore, the size and density of inclusions or defects significantly affect the VHCF behavior of materials. The article presents the experimental results of VHCF tests carried out on a high-strength steel (Örvar Supreme) characterized by a high level of purity. Fully reversed tension-compression fatigue tests were performed by using the ultrasonic testing machine developed at Politecnico di Torino. The experimental results showed that, even if characterized by a high level of purity, the tested steel could fail at a very high number of cycles with nucleation of the fatigue cracks from inclusions found inside the material

Working length transfer in the endodontic clinical practice: A comparative study

8The present paper evaluated the accuracy of two different methods for transferring working length (WL) between manual endodontic instruments and nickel–titanium (NiTi) shaping files. Thirty root canals of extracted permanent teeth were used. Root canals were divided according to canal length (CL) and canal curvature (CC). The reference cusp and the root end were flattened to provide reproducible and accurate measurements. During shaping, the WL measurements were obtained with manual k-files (KF) and transferred to WaveOne (W1) NiTi reciprocating files using the traditional method with the endodontic ruler (method I) and an alternative clinical procedure based on the comparison of the instruments side by side from tip to shank (method II). For each file and each tested method, two measures were taken by two examiners using Rhino (ver. 4.0, McNeel, Seattle, WA, USA) software for a total of 360 (30 × 3 × 2 × 2) measures. Analysis of variance was performed by taking the difference in length (Delta WL, DWL) between files used for the same canal. The difference between methods I and II for WL transfer was found to be statistically significant (df = 1; F = 71.52; p < 0.001). The DWL absolute values obtained with method II were found to be closer to 0 mm (i.e., same length as corresponding KF) than those obtained with method I. Both CL (df = 2; F = 1.27; p = 0.300) and CC (df = 1; F = 2.22; p = 0.149) did not significantly influence WL measurements. With respect to WL transfer, method II seemed to better preserve the correct WL transfer between instruments during the clinical endodontic procedures.openopenMario Alovisi; Mario Dioguardi; Massimo Carossa; Giuseppe Troiano; Maria Chiara Domini; Davide Salvatore Paolino; Giorgio Chiandussi; Elio BeruttiAlovisi, Mario; Dioguardi, Mario; Carossa, Massimo; Troiano, Giuseppe; Chiara Domini, Maria; Paolino, DAVIDE SALVATORE; Chiandussi, Giorgio; Berutti, Eli

Comparison of multi-objective optimization methodologies for engineering applications

Computational models describing the behavior of complex physical systems are often used in the engineering design field to identify better or optimal solutions with respect to previously defined performance criteria. Multi-objective optimization problems arise and the set of optimal compromise solutions (Pareto front) has to be identified by an effective and complete search procedure in order to let the decision maker, the designer, to carry out the best choice. Four multi-objective optimization techniques are analyzed by describing their formulation, advantages and disadvantages. The effectiveness of the selected techniques for engineering design purposes is verified by comparing the results obtained by solving a few benchmarks and a real structural engineering problem concerning an engine bracket of a ca

Topology optimizationwith optimality criteria and transmissible loads.

The paper describes how to take into consideration the presence of transmissible loads in a topology optimization method based on optimality criteria. The optimization problem has been defined as a total potential energy maximization problem with stress, displacement or stiffness constraints. The final volume of the optimal structural configuration has not to be specified a priori and is a consequence of the imposed structural constraints. The implementation of the proposed method is quite simple and leads to the identification of well defined optimal structures. The results obtained by solving several benchmark problems are shown