La "madreña" o lo largo de Asturias

En número dedicado a: El Principado de de Asturia

Numerical support of experimental compact tension test on concrete cylindric specimens

Stanovení rychlosti šíření trhliny v kvazikřehkých materiálech je v posledních letech často studovanou problematikou lomové mechaniky. Článek je zaměřen na porovnání lomových parametrů získaných ze dvou tvarově velmi blízkých lomových zkoušek, a to zkoušky štípáním klínem a zkoušky excentrickým tahem, obě aplikované na cementový kompozit kruhového průřezu. Numerické studie obou zkušebních konfigurací jsou provedeny programem ATENA (MKP). Bylo porovnáno množství energie spotřebované při lomovém procesu u jednotlivých konfigurací.The assessment of crack growth speed in quasi-brittle materials is lately very often studied problem of fracture mechanics. This contribution is focused on comparison of fracture parameters obtained from two fracture tests with similar shape of specimen - wedge splitting test and compact tension test. Both tests are applied on cylindrical specimens made from cement based composite. Numerical simulations for both configurations are performed in software ATENA (FEM). The amount of fracture energy consumed during fracture process has been compared for particular configurations

Scaling Factor Estimation Using an Optimized Mass Change Strategy, Part 1: Theory

In natural input modal analysis, only un-scaled mode shapes can be obtained. The mass change method is, in many cases, the simplest way to estimate the scaling factors, which involves repeated modal testing after changing the mass in different points of the structure where the mode shapes are known. The scaling factors are determined using the natural frequencies and mode shapes of both the modified and the unmodified structure. However, the uncertainty on the scaling factor estimation depends on the modal analysis and the mass change strategy (number, magnitude and location of the masses) used to modify the dynamic behavior of the structure. In this paper, a procedure to optimize the mass change strategy is proposed, which uses the modal parameters (natural frequencies and mode shapes) of the original structure as the basic informatio

Some Methods to Determine Scaled Mode Shapes in Natural Input Modal Analysis

IMAC-XXIII: Conference & Exposition on Structural Dynamics - Structural Health MonitoringWhen the modal model is going to be used for structural modification or for structural response simulation, the scaled mode shapes must be known. If natural input modal analysis is performed, only un-scaled mode shapes can be obtained and an extra method is necessary to obtain the scaling factor. In this paper, two new methods based on mass change are proposed. The first method involves small mass changes in two repeated tests allowing to achieve good accuracy. The second method involves only one mass change and enables the scaling factors of both the modified and unmodified mode shapes to be obtained. Finally, the effect of the normalization used in the mode shapes and the accuracy of each method are analyzed by simulatio

An iterative method to obtain the specimen-independent three-parameter Weibull distribution of strength from bending tests

Brittle materials, such as glass and ceramics, usually present a large strength scatter. Among other probability distributions, the Weibull distribution is widely used to characterize their resistance. Often the two-parameter model is employed, omitting the consideration of a threshold stress, leading to a simplified estimation method. For the sake of generality the present work uses fracture data from bending tests to obtain a three-parameter Weibull distribution function valid for a uni-axially and uniformly tensioned material element. The variable stress state prevailing in the flexural specimen and the size effect are simultaneously accounted for by means of an iterative fitting procedure. The method is extended to account for bimodal flaw distributions, discriminating between edge and surface failure results based on experimental observation. Finally, the model is applied to simulated data sets, obtaining satisfactory results

Visco-hyperelastic model with damage for simulating cyclic thermoplastic elastomers behavior applied to an industrial component

In this work a nonlinear phenomenological visco-hyperelastic model including damage consideration is developed to simulate the behavior of Santoprene 101-73 material. This type of elastomeric material is widely used in the automotive and aeronautic sectors, as it has multiple advantages. However, there are still challenges in properly analyzing the mechanical phenomena that these materials exhibit. To simulate this kind of material a lot of theories have been exposed, but none of them have been endorsed unanimously. In this paper, a new model is presented based on the literature, and on experimental data. The test samples were extracted from an air intake duct component of an automotive engine. Inelastic phenomena such as hyperelasticity, viscoelasticity and damage are considered singularly in this model, thus modifying and improving some relevant models found in the literature. Optimization algorithms were used to find out the model parameter values that lead to the best fit of the experimental curves from the tests. An adequate fitting was obtained for the experimental results of a cyclic uniaxial loading of Santoprene 101-73

Porovnání metod pro analýzu dat z termografických měření meze únavy materiálu Al 2024 pro R=0,1

The traditional methods for fatigue characterization of metallic materials are expensive and extremely time consuming. In order to overcome these shortcomings, the Thermographic Method (TM), based on thermographic analysis, is applied to estimate the fatigue limit of Al 2024. The temperature increase due to localized microplasticity is considered as the fatigue damage indicator. An experimental program is carried out to assess the fatigue limit both as resulting from the S–N field and, directly, from thermographic measurement. For the latter, three different methods are applied for the estimation of the AL 2024 fatigue limit and the out-coming results discussed. The values of fatigue limit predicted from the thermographic method according to the three methods are in good agreement to that derived from the traditional S-N procedure.Stanovení meze únavy kovových materiálů tradičními metodami je ekonomicky a časově velmi náročné. Za účelem snížení časové a finanční zátěže je provedeno srovnání termografické metody (TM) při stanovení cyklické meze únavy hliníkové slitiny AL 2024. V důsledku lokalizace mikroplasticity se zvýší teplota, kterou lze považovat za indikátor vzniku trvalého únavového poškození. Experimenty jsou provedeny ve dvou rovinách. Tradiční cestou jsou změřeny S-N křivky a souběžně jsou provedena termografická měření na materiálu AL 2024. Pro zpracování naměřených dat z TM jsou využity tři dostupné vyhodnocovací metody, známé z literatury. Je hodnocena/diskutována přesnost odhadu/určení meze únavy AL 2024 z jednotlivých metod. Odhad/určení meze únavy z tradičních metod a za použití termografické metody vykazují shodné výsledky