1,721,131 research outputs found
LCF-HCF strain–life model: Statistical distribution and design curves based on the maximum likelihood principle
Full text linkIn the paper, the statistical distribution of the total strain and the fatigue life in the low cycle fatigue (LCF)–high cycle fatigue (HCF) life range is analytically derived starting from the Coffin–Manson and Morrow model. The maximum likelihood principle is exploited for parameter estimation, thus allowing to consider both failures and runout specimens. A straightforward procedure for the estimation of the design curves based on the likelihood ratio confidence lower bound has been also developed. The proposed model has been validated with literature datasets obtained by testing steel and aluminum alloys, proving its effectiveness and representing a reliable alternative to the currently adopted literature models
A new statistical software for the estimation of P-S-N curves in presence of defects: statistical models and experimental validation
Full text linkIt is well-known in the literature that fatigue failures originate from the weakest element within the component loaded volume. In particular, for metallic materials the fatigue crack typically nucleates from the most critical surface defect in the High-Cycle-Fatigue (HCF) region; whereas, it generally nucleates from the most critical internal defect in the Very-High-Cycle-Fatigue (VHCF) region, at stress amplitudes below the so-called 'transition stress amplitude'. Therefore, regardless of the fatigue region, the P-S-N curves must necessarily take into account the random distribution of the critical defect size. However, in the literature, there are few statistical models that can model the dependency between the fatigue life and the defect size or that can take into account the presence of different failure mechanisms (e.g., surface crack nucleation in HCF and internal crack nucleation in VHCF). In the present paper, a new software for the estimation of the P-S-N curves is proposed. The statistical P-S-N models recently proposed by the authors and implemented in the software are described in the paper. The procedure for the parameter estimation is also explained in detail and the software is finally validated with experimental datasets collected by the authors or available in the literature
Combined NMR-crystallographic investigation of the inclusion of molsidomine into a-, b- and g-cyclodextrins
No full textA NMR spectroscopic and crystallographic investigation supported by molecular modelling methods has been employed to describe the inclusion properties of molsidomine into the three underivatized a-, b- and c-cyclodextrins, aimed to point out the factors affecting the complexation selectivity and stabilization. The NMR results were compared and validated by the analysis of
crystallographic data as retrieved from the Cambridge Structural Database and molecular modelling studies
Very high cycle fatigue life and critical defect size: Modeling of statistical size effects
Full text linkA novel statistical approach to model size effects in very high cycle fatigue (VHCF) is proposed in the paper. The statistical distributions of the VHCF life and of the size of the defect leading to VHCF failure (critical defect) are identified in the paper through the weakest-link principle. The statistical distributions are able to account for the stress gradients that are present in a loaded material volume. An efficient procedure for estimating the parameters involved in the statistical distributions is also shown. The proposed statistical models are finally validated through experimental data taken from the literature. The experimental validation proves the fitting capability of the proposed models that outperform the traditional models based on the 90% risk-volume
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Static strength of brittle materials under multiaxial nonuniform stress states: A novel statistical model for assessing size effects
No full textIn this paper, a model for the assessment of size effects on quasi-static strength of brittle materials subjected to applied load inducing a nonuniform stress distribution within the material volume is proposed. An equivalent stress computed through finite element analysis is introduced in the model to account for the effect of the stress gradient within the loaded volume. The defect size distribution is modelled, differently from the literature, with the largest extreme value distribution. The proposed model has been validated with datasets available in the literature and obtained through bending tests on concrete specimens. For each type of test, the model permits to properly assess size effects. Due to its general formulation, a model for the strength variation with respect to the loaded volume, regardless of the testing type, was also obtained, further proving its effectiveness
Residual properties in damaged laminated composites through nondestructive testing: A review
Full text linkThe development of damage tolerance strategies in the design of composite structures constitutes a major challenge for the widespread application of composite materials. Damage tolerance approaches require a proper combination of material behavior description and nondestructive techniques. In contrast to metals, strength degradation approaches, i.e., the residual strength in pres-ence of cracks, are not straightforwardly enforceable in composites. The nonhomogeneous nature of such materials gives rise to several failure mechanisms and, therefore, the definition of an ulti-mate load carrying capacity is ambiguous. Nondestructive techniques are thus increasingly re-quired, where the damage severity is quantified not only in terms of damage extension, but also in terms of material response of the damaged region. Based on different approaches, many nonde-structive techniques have been proposed in the literature, which are able to provide a quantitative description of the material state. In the present paper, a review of such nondestructive techniques for laminated composites is presented. The main objective is to analyze the damage indexes related to each method and to point out their significance with respect to the residual mechanical perfor-mances, as a result of the working principle of each retained technique. A possible guide for future research on this subject is thus outlined
Size-Effects on the VHCF Response of Flat Metallic Specimens for Automotive Applications: Analysis of Fatigue Data with a Method Based on the Stress Gradient
Full text linkThe design against fatigue failures at very high number of cycles (VHCF) is fundamental to guarantee the integrity of components used in structural applications (aerospace, energy production, automotive). Experimental tests to assess the VHCF response of materials are generally carried out on small specimens with sizes that are significantly different from those of the components to be designed. Size-effect, which is widely known to affect the VHCF response, must therefore be properly modeled and accounted when components are designed to ensure their structural integrity. Size-effects in VHCF have been generally investigated by testing specimens with circular cross-sections and modeled by considering the probabilistic increment of the defect size with the loaded volume. In the present paper, ultrasonic fatigue tests have been carried out on hourglass flat specimens and larger dog-bone flat specimens to investigate size-effects. One aluminum alloy and four steels used for automotive applications have been tested. The experimental results have been analyzed with an innovative statistical model based on the weakest-link principle and on the stress gradient within the specimens, which does not require the size of the defect at the origin of the fatigue failure, generally not available if the specimen fails from the surface. Size-effects were found to significantly influence the VHCF response of the investigated materials, further confirming that it is strongly material dependent, even for flat specimens. A general rule for size-effect in VHCF of flat specimens was not found, proving that it must be properly experimentally verified and safely accounted when designing large components against VHCF failure
- …
