1,721,020 research outputs found
Damaging mechanisms and constitutive modeling of metal-matrix composites
No full textThe overall mechanical behavior of metal-matrix composites beyond the elastic threshold is often hypothesized to be dominated by metal ductility. However, the progressive loss of elastic stiffness for repeated loading-unloading cycles, which has been evidenced by the output of some mechanical testing, rather suggests quasi-brittle response typical of ceramics. The consequences of these alternative assumptions are discussed in this contribution on the basis of the results of simulated indentation tests, which induce significant triaxial stress states. The possibility of identifying the actual failure mode of these materials by combined experimental and computational work is assesses with specific reference to the predictive capacity of constitutive models implemented in widely available computer codes
Characterization methodology in nondestructive structural monitoring of concrete bridges
Full text linkMonitoring of concrete bridges has been a common practice in recent years. Nondestructive measurement methods are one of the techniques for controlling the technical condition of bridges, especially when the structures are 50 years old or more. Within such context, one of the most commonly used techniques is the analysis of the dynamic response of the structure during its operative conditions. The measurement
of displacements and accelerations resulting from excitation by natural road traffic or as a result of excitation with special exciters is the basis for modal analysis and classic material identification method. In this work, the dynamic analysis of bridges, whose structure has undergone significant deterioration and requires to be checked for technical conditions, is analyzed. The most frequently sought parameters are material density, necessary to determine the self-weight of the structure, and material stiffness, which is most often deteriorated as a result of harmful chemical compounds and long-term cyclic loads. If one would like to take into account the different degree of deterioration in different parts of the bridge, then the task becomes not only poorly formulated, but also the optimization problem is often non-convex, which makes the identification of material parameters based on the measured dynamic responses difficult or even impossible. Determining the parameters of the model in such an inverse problem becomes possible when the static measurements are added to the set of dynamic data.
This paper presents a complete procedure for the mechanical characterization of a technically deteriorated bridge with the assumed geometry. The optimal selection of the location of acce lerometers on the structure, as well as the accuracy ranges of individual configurations of measuring sensors, are presented. Moreover, easy to perform additional static measurements are proposed, in order to provide regularization of the inverse
problem. Using the sensitivity analysis and advanced global optimization techniques based on Gaussian processes, the proposed methodology allows for the unambiguous and simultaneous determination of material densities and degraded stiffnesses in different, pre-selected parts of the bridge model. For all analyses, the finite element method, modal analysis and inverse methods using Gaussian processes are used. The full procedure is prepared by the authors in the Matlab environment and can be extended to any bridge geometry with any number of separated zones in which the concrete is deteriorated to varying degrees. The effectiveness of the procedure is checked on synthetic data and verified on the examples from literature data
Fracture of corrosion protecting layers: Investigation by indentation test
No full textThe mechanical properties of protective coatings produced by corrosion on the internal surfaces of pipelines transporting hydrocarbons have been investigated by indentation tests, which have revealed the spall or cracking attitude of the film. The role of material properties controlling the coating integrity and the main damaging mechanisms have been identified with the aid of the numerical simulation of the experiment
Mixed-mode delamination with large displacement modeling of fiber-bridging
No full textCrack bridging mechanisms, such as fiber-bridging and fibrillation, take place in many different types of interfaces upon the development of large relative displacements between the separating faces. Cohesive models that do not account for these mechanisms inevitably underestimate the interface strength. On the other hand, consideration of large interface openings implies tackling a number of mechanical and geometrical difficulties, conflicting with the basic assumptions behind the cohesive model. A simple strategy to deal with large openings and fiber-bridging in cohesive models is discussed in the present contribution. A recently proposed cohesive model for mixed-mode delamination is used to model the interface behavior until the normal opening remains small, while the remaining cohesive energy is transferred to a co-linear fibril element when a critical opening threshold is reached. The initial use of a mixed-mode cohesive model allows to correctly define the complex evolution of the fracture energy with the mode-ratio in the initial, short range phase of the cohesive resistance, while the fibril correctly models the interface behavior in the final, long range phase, where crack bridging mechanisms are dominant. Some preliminary numerical examples confirm the accuracy and robustness of the proposed procedure
Nondestructive structural monitoring of bridges based on artificial intelligence
Full text linkNon-destructive measurement techniques have been used for decades to assess the deterioration of various critical infrastructure such as bridges. The cause of deterioration does not have to be overload, resulting from increasingly frequent extreme weather conditions, but rather more and more intensive road traffic with an ever-increasing number of heavy transport vehicles. In addition, reinforced concrete often undergoes destructive chemical processes (e.g., alkali silica reactions), which significantly affect the progressive degradation of its mechanical properties.
The lack of the need to take physical samples, which by cutting, leads to local damage to the structure,
is one of the biggest advantages of nondestructive solution, here considered. In addition, the possibility
of assessing the quality of the structure on site saves time necessary for laborious analysis of results or laboratory strength tests of many material samples. However, in order to be able to assess the technical condition of any structure, one must first prepare a full measurement procedure, choose the best location for mounting the measuring sensors, correctly collect all measurement data and consistently interpret the results, and also have an a priori calculation model to be used in the identification procedure.
In this paper, it is assumed that the identification procedure is already known. The structure of the investigated bridge is also known and the computational model of a specific bridge is already built and precisely reflects the behavior of the structure. Here, the focus is on finding the best method to build a substitute model, whose task is to quickly determine in situ the technical condition of the structure. For this purpose, various techniques of creating surrogates based on artificial neural networks are used. From the simplest construction of shallow networks to more advanced Bayesian networks and networks with radial basis functions. The effectiveness of the substitute models is checked on synthetic data and verified on the example of literature data
Su diagnosi strutturale e caratterizzazione di materiali effettuate mediante prove di indentazione non-distruttive e analisi inverse
No full textQuasi-non-destructive small punch and hole drilling tests extended to the assessment of both material properties and residual stresses
No full textLarge diameter monopile buckling due to localized force. A numerical study.
No full textIn the last decade, the industry of fixed offshore wind farms has developed significantly, leading
to important reductions of the global cost of the plants. Generally speaking, about 30% of the
total cost of a wind offshore plant, including the installation activities, is related to foundations.
In the view of optimising the management of the plant, strong efforts have been done to reduce
the costs of the foundation, preserving the planned design while assuring a safe and reliable
performance. From the practical point of view, the most diffused foundation, i.e., the monopile,
is of special interest. Cost optimisation of the foundation suggests to increase the diameter and
to reduce the wall thickness of the monopile, increasing the risk of pile tip damage, particularly
frequent in soils where localized inclusions like flints or boulders are present. A higher potential
tip damage is the undesired counterpart of the geometry optimisation and it may induce
unacceptable economic consequences. This study, based on numerical analyses, is focalized
on the buckling of the pile tip subjected to a variously inclined localized force, acting on the
edge of the pile base. Results are collected in diagrams, which can be used in design
procedures
Influence of humidity and temperature on mechanical properties of corrugated board - Numerical investigation
No full textPaper is a material whose mechanical properties are highly dependent on humidity and temperature, naturally building the relationship between the stiffness and strength of corrugated board and changing weather conditions. In this paper, attention is focused on the dependence of the physical properties of the cardboard on changes in humidity and temperature, which undergo dynamic fluctuations both during the production of corrugated board and during its storage. Two techniques were used to test this effect, namely numerical homogenization and global sensitivity analysis. Both methods were implemented to determine the theoretical relationships between the change in humidity and/or temperature in each layer of corrugated board and its global bending, compression, and shear stiffness. The procedure was used to analyze different types of 5-ply and 3-ply cardboard. The obtained results allowed the authors to build a complete map of the relationship between the change in humidity of selected layers and the strength characteristics of the full assembly
Impact of Temperature and Humidity on Key Mechanical Properties of Corrugated Board
Full text linkThis research explores how temperature and relative humidity impact the mechanical properties of corrugated cardboard. Samples were treated under a range of controlled climate conditions in a climate chamber to simulate varying environmental exposures. Following this conditioning, we performed a series of mechanical tests: the Edge Crush Test (ECT) to assess compressive strength, four-point Bending Tests (BNTs) in both the Machine (MD) and Cross Directions (CD) to evaluate bending stiffness, Sample Torsion Tests (SSTs) for shear stiffness, and Transverse Shear Tests (TSTs) to measure torsional rigidity. By comparing results across these tests, we aim to determine which mechanical property shows the highest sensitivity to changes in humidity levels. Findings from this study are expected to offer valuable insights into the environmental adaptability of corrugated board, particularly for applications in packaging and storage, where climate variability can affect material performance and durability. Such insights will support the development of more robust and adaptable packaging solutions optimised for specific climate conditions
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