Papers by Keyword: Local Damage

Abstract: The method of structural vulnerability assessment presented in this paper is closely in accordance with the definition based on two aspects, strain energy of structure and damage demand of members. The search process of damage scenarios was carried out by an example of truss structure, and the results of analyses included importance factor of members, damage scenarios with the minimum number of killed members, and local damage occurred in advance. The influence of loading on member importance factor and vulnerability index was discussed and it showed that though with the agreement of general trend, the rank of importance factor or VI index under a specified scenario varied greatly. The analysis could be utilized as the proof of measures to enhance structural capacity to meet the extreme event.

Abstract: This study presents the local damage of ultra high strength fiber reinforced concrete plates. Impact test of the reinforced concrete plates using two different short fibers are conducted to examine the failure behavior and impact resistant performance. Material models are discussed and proposed by simulating the high speed tri-compressive and uni-tensile tests. Numerical simulations of the impact tests are carried out. Numerical results show good agreements with the test results.

Abstract: Free cutting steels belong to a family associated with hot workability problems. This study has focused on the analysis of microstructural features located near the surface of the billet before and after reheating and how they can affect the nucleation/propagation of damage during initial hot working operations. The work has been done with free cutting steels containing sulfur contents ranging from 0.32 to 0.42%. The relevance of clustering of inclusions, their location at grain boundaries or triple points and the influence of softening mechanisms (as recrystallization) have been considered with the help of several parameters determined by image analysis techniques.

Abstract: This paper describes the projectile impact resistance of cement based composite slabs. The resistance is evaluated on the basis of the presented experimental program. In the experiment, local damage was inflicted by impact of defined projectiles on specimens made from normal strength concrete (NSC), steel fiber-reinforced concrete (FRC), ultra-high performance concrete (UHPC) and ultra-high performance fiber-reinforced concrete (UHPFRC) with different fiber content. Deformable ogive-nose projectiles with diameter of 7.92 mm and mass of 8.04 g with impact velocity about 700 m/s were in the experiment hitting center of the specimens. Data from the measured and visual evaluation of specimen damage were used for comparison of specimen projectile impact resistance in relation to the used material.

Abstract: Raw vibration signals measured on the machine housing in industrial conditions are complex and can be modeled as an additive mixture of several processes (with different statistical properties) related to normal operation of machine, damage related to one (or more) of its part, some noise, etc. In the case of local damage in rotating machines, contribution of informative process related to damage is hidden in the raw signal so its detection is difficult. In this paper we propose to use the statistical modeling of vibration time series to identify these components. Building the model of raw signal may be ineffective. It is proposed to decompose signal into set of narrowband sub-signals using time-frequency representation. Next, it is proposed to model each sub-signal in the given frequency range and classify all signals using their statistical properties. We have used several parameters (called selectors because they will be used for selection of sub-signals from time-frequency map for further processing) for analysis of sub-signals. They have base in statistics theory and can be useful for example in testing of normality of data set (vibration time series from machine in good condition is close to Gaussian, damaged not). Results of such modeling will be used in the sub-signals classification procedure but also in defects detection. We illustrate effectiveness of novel technique using real data from heavy machinery system.

Abstract: The crack is easily generated in the metal structure because of fatigue. It has a strong impact on structural safety. To reduce accident and losses, it is important to detect the local damage such as active crack. The general method to detect the local damage is acoustic-emission technique. But it has the disadvantages of short distance transmission, interfered easily and so on. In this paper, the fiber optic acoustic emission sensor system is designed and developed. A lot of experiments have been done in laboratory. It is shown that the new system has long distance transmission, and has high anti-interference etc. It can meet the demand of local damage detection about the metal structure.

Abstract: The stability of steel columns that have suffered localized damage is investigated through analytical and computational means. An analytical model based on the Rayleigh-Ritz technique is used in conjunction with detailed finite element models to study the effect of damage extent and location on column load carrying capacity. Analytical and simulation results show a severe reduction in column axial resistance in the presence of localized flange loss.

Abstract: In order to find out the limit depth that locally damaged submarine can dive, the model of ring-stiffened cylindrical shell with local indentation was proposed. The limit load of model were calculated and compared with ideal ring-stiffened cylindrical shell. In order to assess the residual limit load of the ring-stiffened cylindrical shell, a residual limit load coefficient is proposed and a series of curves of the coefficient are drawn.

Abstract: The double-shell structure under high temperature will lead to structural changes in material properties. Thermal expansion causes the production of thermal stress of the additional constraints bar, whose security research is the aim of this paper. The paper chooses Laoshan Velodrome Olympic venues as the research object, dividing the temperature zones of shell structure, and conducting the FDS simulation temperature field. The internal temperature of structural elements of computational shell in various zones will be in accordance with the first constant load and dead load after warming loading method to give a finite element analysis and give an evaluation of the safety of shell structure. The results show that: the temperature of the fire scenarioⅠis significantly higher than that of the fire scenario Ⅱ.We selecte the temperature of the fire scenario Ⅱ as the temperature load, and find that the local damage of six bars in the high-temperature zone occurs, which won’t cause structural damage to the whole structure. Therefore, these 6 bars need to be sprayed with fire retardant coating.

Abstract: The paper shows application of an adaptive filter as a pre-processor for impulsive cyclic weak signal recovery from raw vibration signals captured from complex mechanical systems used in the industry (namely bearings used in pulleys – parts of driving units for belt conveyors). Periodic/cyclic impulses are related to local faults which cause impulse/concentric forces/stresses in kinematic pairs. Typical examples of such local faults which cause mechanical system condition change are spall/pitting on bearings elements: outer/inner races and/or rolling elements. For analyzed objects, impulses associated with local faults are masked by other signal sources. In the first part of the paper are presented objects for the better understanding of mechanical phenomena that exist in the system, then preliminary signal analysis will be performed (in time, frequency and time-frequency domain) for the identification of signal nature. Next the idea of an adaptive system and the brief description of Normalized Least Mean Square (NLMS) algorithm will be presented. Application of NLMS is better than classical LMS due to stability of the adaptation. In the last section the results of adaptive filtering for signals from bearings is discussed. Authors show application of NLMS (for the first time in literature) for the case when signals are received from machines working in industrial condition. There were made only trails when the machines were investigated in laboratory conditions.