Applied Mechanics doi: 10.3390/applmech1040013

Authors: Ayodeji Olamide Abdeldjalil Bennecer Stefan Kaczmarczyk

Fatigue lifetime of offshore pipelines with semi-elliptical circumferential surface cracks is often underestimated. An accurate prediction of the pipeline structural integrity is nevertheless important in order to prevent unnecessary and expensive downtime, failures leading to leakage or spillage of pipeline contents to the surrounding environment, and ultimately improve the reliability of the pipeline. The estimation of crack growth in pipelines under varying loads is highly dependent on the calculation of crack driving parameters, such as the stress intensity factor and the crack tip opening displacement (CTOD) using the 3D J-integral or its equivalent. This paper presents a numerical study to predict the fatigue lifetime of cracks in pipes, determining the J-integral that includes first and second derivatives of the displacement field for pipes containing a range of circumferential surface cracks. A pipe segment is structurally loaded and stress intensity factors (SIF) evaluated using the finite element method (FEM). Based on the results, a number-of-cycles to failure curve shows a longer lifetime than previously predicted by about 5% for a pipe with semi-elliptical external surface cracks. In addition, they indicate that the external short cracks are more dangerous than the internal long surface crack hereby requiring earlier assessment.

]]>Applied Mechanics doi: 10.3390/applmech1040012

Authors: Nedaa Amraish Andreas Reisinger Dieter H. Pahr

Digital image correlation (DIC) systems have been used in many engineering fields to obtain surface full-field strain distribution. However, noise affects the accuracy and precision of the measurements due to many factors. The aim of this study was to find out how different filtering options; namely, simple mean filtering, Gaussian mean filtering and Gaussian low-pass filtering (LPF), reduce noise while maintaining the full-field information based on constant, linear and quadratic strain fields. Investigations are done in two steps. First, linear and quadratic strain fields with and without noise are simulated and projected to discrete measurement points which build up strain window sizes consisting of 6&times;5, 12&times;11, and 26&times;17 points. Optimal filter sizes are computed for each filter strategy, strain field type, and strain windows size, with minimal impairment of the signal information. Second, these filter sizes are used to filter full-field strain distributions of steel samples under tensile tests by using an ARAMIS DIC system to show their practical applicability. Results for the first part show that for a typical 12&times;11 strain window, simple mean filtering achieves an error reduction of 66&ndash;69%, Gaussian mean filtering of 72&ndash;75%, and Gaussian LPF of 66&ndash;69%. If optimized filters are used for DIC measurements on steel samples, the total strain error can be reduced from initial 240&minus;300 &mu;strain to 100&ndash;150 &mu;strain. In conclusion, the noise-floor of DIC signals is considerable and the preferable filters were a simple mean with s*&macr; = 2, a Gaussian mean with &sigma;*&macr; = 1.7, and a Gaussian LPF with D0*&macr; = 2.5 in the examined cases.

]]>Applied Mechanics doi: 10.3390/applmech1030011

Authors: Jeongeun Son Dongping Du Yuncheng Du

Uncertainty quantification (UQ) is an important part of mathematical modeling and simulations, which quantifies the impact of parametric uncertainty on model predictions. This paper presents an efficient approach for polynomial chaos expansion (PCE) based UQ method in biological systems. For PCE, the key step is the stochastic Galerkin (SG) projection, which yields a family of deterministic models of PCE coefficients to describe the original stochastic system. When dealing with systems that involve nonpolynomial terms and many uncertainties, the SG-based PCE is computationally prohibitive because it often involves high-dimensional integrals. To address this, a generalized dimension reduction method (gDRM) is coupled with quadrature rules to convert a high-dimensional integral in the SG into a few lower dimensional ones that can be rapidly solved. The performance of the algorithm is validated with two examples describing the dynamic behavior of cells. Compared to other UQ techniques (e.g., nonintrusive PCE), the results show the potential of the algorithm to tackle UQ in more complicated biological systems.

]]>Applied Mechanics doi: 10.3390/applmech1020010

Authors: Duong Huong Nguyen Long Viet Ho Thanh Bui-Tien Guido De Roeck Magd Abdel Wahab

Damage can be detected by vibration responses of a structure. Damage changes the modal properties such as natural frequencies, mode shapes, and damping ratios. Natural frequency is one of the most frequently used damage indicators. In this paper, the natural frequency is used to monitor damage in a free-free beam. The modal properties of the intact free-free beam are identified based on a setup of 15 accelerometers. A finite element model is used to model the free-free beam. Three models are considered: beam (1D), shell (2D), and solid (3D). The numerical models are updated based on the first five bending natural frequencies. The free-free beam is damaged by a rectangle cut. The experiment is re-setup and the model properties of the damaged beam are re-identified. The cuttings are modeled in the numerical simulations. The first five numerical bending natural frequencies of the damaged beam are compared with the experimental ones. The results showed that the 1D beam element model has the highest errors, while the 2D and 3D models have approximately the same results. Therefore, the 2D representation can be used to model the damaged beam for fast computation.

]]>Applied Mechanics doi: 10.3390/applmech1020009

Authors: José Manuel Pérez-Canosa Santiago Iglesias-Baniela Alsira Salgado-Don

Heavy cargo units with a relatively reduced footprint area require a support surface large enough to transfer the forces onto the largest possible surface and/or the main stiffening (longitudinal and transverse) in order to not collapse or overstress the ship&rsquo;s structure and, consequently, put the ship, the cargo, and the crew at risk. For that reason, it is necessary to project stowage and securing systems (including bedding design) to ensure that, by applying the principles of good seamanship and securing practices, the shipment is maintained in a safe condition throughout the trip until destination port arrival. Despite the increase in project cargo shipments in recent years, in many cases, International Maritime Organization (IMO) regulations are followed by default. The main purpose of this paper, thus, is to highlight certain shipments for which IMO guidelines should be taken into account in future revisions. This is done through what was considered innovative project cargo on a particular ship due to its special characteristics. To this end, because of limitations found in the IMO CSS Code regarding acceleration and force calculations, it was necessary to resort to the internationally accepted guidelines of one of the strictest classification societies.

]]>Applied Mechanics doi: 10.3390/applmech1020008

Authors: Aaron S. Blumenthal Michael Nosonovsky

The tower clocks designed and built in Europe starting from the end of the 13th century employed the &ldquo;verge and foliot escapement&rdquo; mechanism. This mechanism provided a relatively low accuracy of time measurement. The introduction of the pendulum into the clock mechanism by Christiaan Huygens in 1658&ndash;1673 improved the accuracy by about 30 times. The improvement is attributed to the isochronicity of small linear vibrations of a mathematical pendulum. We develop a mathematical model of both mechanisms. Using scaling arguments, we show that the introduction of the pendulum resulted in accuracy improvement by approximately &pi;/&mu; &asymp; 30 times, where &mu; &asymp; 0.1 is the coefficient of friction. Several historic clocks are discussed, as well as the implications of both mechanisms to the history of science and technology.

]]>Applied Mechanics doi: 10.3390/applmech1020007

Authors: Stefanos C. Spathopoulos Georgios E. Stavroulakis

Sheet metal forming is one of the most important manufacturing processes applied in many industrial sectors, with the most prevalent being the automotive and aerospace industries. The main purpose of that operation is to produce a desired formed shape blank, without any material failures, which should lie well within the acceptable tolerance limits. Springback is affected by factors such as material properties, sheet thickness, forming tools geometry, contact and friction, etc. The present paper proposes a novel neural network system for the prediction of springback in sheet metal forming processes. It is based on Bayesian regularized backpropagation networks, which have not been tested in the literature, according to the authors&rsquo; best knowledge. For the creation of training examples a carefully prepared Finite Element model has been created and validated for a test case used in similar industrial studies.

]]>Applied Mechanics doi: 10.3390/applmech1010006

Authors: Luís Bernardo Cátia Taborda

The Generalized Softened Variable Angle Truss Model (GSVATM) allows one to compute the global behavior of reinforced concrete (RC) beams under torsion, including the pre- and post-cracking stage. In a previous study, such a model was successfully extended to cover prestressed concrete beams under torsion with longitudinal and uniform prestress. In order to continue to extend the theoretical model for other loading cases, in this article, the GSVATM is extended to cover RC beams under torsion combined with external and centered axial forces. The changes in GSVATM are presented, as well as the modified calculation solution procedure. Some theoretical predictions from the extended GSVATM are compared with numerical results from the non-linear finite element method (FEM), where good agreement is observed for the studied trends.

]]>Applied Mechanics doi: 10.3390/applmech1010005

Authors: Aleksandr Cherniaev Svetlana Pavlova Aleksandr Pavlov Valeriy Komarov

Assessments of residual load-carrying capacity are often conducted for composite structural components that have received impact damage. The availability of a verified simulation methodology can provide significant cost savings when such assessments are required. To support the development of a reliable and accurate simulation methodology, this study investigated the predictive capabilities of a stacked solid-shell finite element model of a cylindrical composite component with a damage mechanics-based description of the intra-ply material response and a cohesive contact model used for simulation of the inter-ply behavior. Identification of material properties for the model was conducted through mechanical characterization. Special attention was paid to understanding the influence of non-physical parameters of the intra- and inter-ply material models on predicting compressive failure load of damaged composite cylinders. Calibration of the model conducted using the response surface methodology allowed for identifying rational values of the non-physical parameters. The results of simulations with the identified and calibrated finite element model showed reasonable correlation with experimental data in terms of the predicted failure loads and post-impact and post-failure damage modes. The investigated modeling technique can be recommended for evaluating the residual load-bearing capacity of flat and curved composite parts with impact damage working under the action of compressive loads.

]]>Applied Mechanics doi: 10.3390/applmech1010004

Authors: Laddu Bhagya Jayasinghe Daniele Waldmann Junlong Shang

Pile punching (or driving) affects the surrounding area where piles and adjacent piles can be displaced out of their original positions, due to horizontal loads, thereby leading to hazardous outcomes. This paper presents a three-dimensional (3D) coupled Smoothed Particle Hydrodynamics and Finite Element Method (SPH-FEM) model, which was established to investigate pile punching and its impact on adjacent piles subjected to lateral loads. This approach handles the large distortions by avoiding mesh tangling and remeshing, contributing greatly high computational efficiency. The SPH-FEM model was validated against field measurements. The results of this study indicated that the soil type in which piles were embedded affected the interaction between piles during the pile punching. A comprehensive parametric study was carried out to evaluate the impact of soil properties on the displacement of piles due to the punching of an adjacent pile. It was found that the interaction between piles was comparatively weak when the piles were driven in stiff clays; while the pile-soil interactions were much more significant in sandy soils and soft clays.

]]>Applied Mechanics doi: 10.3390/applmech1010003

Authors: Mario Buchely Alejandro Marañon

In recent years, Spherical Cavity Expansion (SCE) theory has been extensively utilized to model dynamic deformation processes related to indentation and penetration problems in many fields. In this review, the SCE theory is introduced by explaining the different mathematical features of this theory, its solution, and a potential application to model the penetration of a rigid penetrator into a deformable target. First, a chronologically literature review of the most common models used to study this kind of penetration problems is introduced, focusing on the SCE theory. Then, the engineering model of penetration is presented using the SCE approach. The model is then compared and validated with some FE numerical simulations and with previous penetration results. It is concluded that this engineering model based on the SCE theory can be utilized to predict the projectile deceleration and penetration depth into the semi-infinite and finite targets impacted by rigid penetrators.

]]>Applied Mechanics doi: 10.3390/applmech1010002

Authors: Abbas Tamadon Dirk J. Pons Don Clucas

Material flow transportation around the rotating tool and the mass deposition at the backside of the tool are critical characteristics of friction stir welding. To achieve an optimized weld structure, the history of the plastic deformation needs to be identified with a flow-based elucidation. In this study, an analogue model was applied to evaluate the formation of a banded structure using the bobbin tool, with a focus on the interaction between the tool-workpiece. The flow visualization in plasticine analogue was validated in comparison with the aluminium welds. The plastic flow mechanism was visualized both, at the surface and the cross-section of the weld-seam. The cross-section of the weld shows the details of the formation of tunnel voids, caused by the failure of the flow regimes. A physical model of the material flow was proposed to explain the formation mechanism of the tunnel void as a discontinuity during the mass refilling at the rear of the tool.

]]>Applied Mechanics doi: 10.3390/applmech1010001

Authors: Magd Abdel Wahab

Mechanics is a branch of physics that describes the theoretical aspects related to the response of objects to external forces and displacements [...]

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