Detailed Stress Research Articles

Micromechanical finite element analysis of effect of multilayer interphase on crack propagation in SiC/SiC composites

The current study presents a micromechanical methodology to analyze the cracking behavior of a SiC/SiC composite with multilayer interphase using finite element method. To capture the constituent level damage initiation and propagation within the multilayer interphase, an axisymmetric unit-cell model was developed by discreetly modeling the fiber, the matrix, and the sublayers of interphase. Moreover, the cracking inside the interphase and debonding at the interfaces between different constituents were taken into account. The extended finite element method (XFEM) was applied to model the cracking inside the interphase and matrix. The cohesive surface approach was employed to describe the debonding behavior at all the interfaces. Adopting the proposed numerical approach, detailed local stress state and cracking behavior of SiC/SiC composites with multilayer interphase were analyzed. The results show that the multilayer interphase has a significant effect on the cracking behavior. Moreover, the growth length of secondary cracks had been demonstrated to be a useful parameter that is capable of connecting composites level behaviors and constituent level damages. From the various numerical methods used, the finite element simulation in conjunction with the XFEM and the cohesive surface approach is a precise and consistent way to analyze the crack propagation and prediction of failure for composites with multilayer interphase. The research provides a fundamental method for promoting the interphase design of SiC/SiC composites.

A Deep Learning Method for Vision Based Force Prediction of a Soft Fin Ray Gripper Using Simulation Data.

Soft robotic grippers are increasingly desired in applications that involve grasping of complex and deformable objects. However, their flexible nature and non-linear dynamics makes the modelling and control difficult. Numerical techniques such as Finite Element Analysis (FEA) present an accurate way of modelling complex deformations. However, FEA approaches are computationally expensive and consequently challenging to employ for real-time control tasks. Existing analytical techniques simplify the modelling by approximating the deformed gripper geometry. Although this approach is less computationally demanding, it is limited in design scope and can lead to larger estimation errors. In this paper, we present a learning based framework that is able to predict contact forces as well as stress distribution from soft Fin Ray Effect (FRE) finger images in real-time. These images are used to learn internal representations for deformations using a deep neural encoder, which are further decoded to contact forces and stress maps using separate branches. The entire network is jointly learned in an end-to-end fashion. In order to address the challenge of having sufficient labelled data for training, we employ FEA to generate simulated images to supervise our framework. This leads to an accurate prediction, faster inference and availability of large and diverse data for better generalisability. Furthermore, our approach is able to predict a detailed stress distribution that can guide grasp planning, which would be particularly useful for delicate objects. Our proposed approach is validated by comparing the predicted contact forces to the computed ground-truth forces from FEA as well as real force sensor. We rigorously evaluate the performance of our approach under variations in contact point, object material, object shape, viewing angle, and level of occlusion.

Crack growth models for multiaxial fatigue in a ship’s propeller shaft

A premature fatigue failure of a large intermediate propeller shaft in a shuttle tanker is discussed and analyzed. The short fatigue life consists mainly of a crack growth phase. Life predictions are carried out by crack growth modelling based on engineering fracture mechanics. The purpose of the present investigation is to identify the most likely loading modes based on the evolution of the crack propagation. A Linear Elastic Fracture Mechanics Model (LEFM) is applied with the stress intensity factor range entering the Paris law as a key parameter. Existing formulas for the geometry functions are supplemented by more detailed stress intensity factor calculations pertaining to small semi-elliptical surface cracks subjected to stress mode I. Enhanced geometry functions are proposed as a function of the relative crack depth and the crack shape aspect ratio. The ability of the fracture mechanics model to reconstruct the observed crack path and crack shape development is emphasized. Various loading modes and multi-axial stress states are applied to pursue the observed crack behavior. The observed semi-elliptical crack shapes and the shift in crack planes are included in the analysis.

Artificial Neural Network Plan for Transmission Tower Structure Safety Assessment

The security of transmission tower structure is the foundation to ensure the safe operation of power grid. The research of fuzzy qualitative assessment method for the structural health of transmission towers is the basic work of large-scale digital power grid engineering. In this paper, artificial neural network (ANN) is used as a generalized tool for structural health assessment of transmission towers. The feasibility of using artificial neural network to qualitatively evaluate the structural health of transmission towers is verified by numerical simulation data. In order to train the artificial neural network, the displacement, stress and other signals generated by the finite element model are calculated and used as the training input of the artificial neural network. The detailed stress results of the finite element model are calculated as the qualitative evaluation basis of the structural health, and the training output of the artificial neural network is generated. By the same method, the test set is generated, and it is found that the artificial neural network is feasible for the fuzzy qualitative assessment of the structural health of transmission tower, and the misstatement rate is less than 5%.

Effect of base shear and moment on lateral dynamic behavior of monopiles

The base shear and moment may play important roles in behaviors of offshore monopiles, and traditional p-y curves cannot model the base forces. In this study, a new semi-analytical model for monopile is proposed, from which base forces and displacements can all be obtained simultaneously. Green's functions for poro-visco-elastic soil and Timoshenko beam are used. Full bond between pile and soil is assumed, which means the results are suitable for the normal operating conditions for offshore wind turbines. Selected numerical results are examined for different pile lengths, pile thickness, load eccentricity, soil parameters and frequencies of excitation. These results show the values of base forces are notable only when the pile's aspect ratio is very small. Besides, an interesting phenomenon is found: Ignoring the base effects will only lead to a negligible influence on pile impedances and responses, even when the pile's aspect ratio is very small. The reason is that the pile shaft near the base in the “no base effect” model will take the stresses the base bears in the “with base effect” model. The pile's overall responses and impedances are not sensitive to the detailed stress distributions around the pile base in this elasto-dynamic problem.

Towards selective laser paint stripping using shock waves produced by laser-plasma interaction for aeronautical applications on AA 2024 based substrates

Laser stripping is a process which typically includes different forms of ablation phenomena. The presented work investigates a mechanical stripping process using high pressure laser-induced shock waves in a water confined regime. Power density is studied as a parameter for selective laser stripping on painted specimens and for adhesion relations with single layer epoxy targets. A flashlamp-pumped Nd:YAG laser with fixed spot size (4 mm) is shot on single layer epoxy and several layers of polymeric paint applied on a AA 2024-T3 (Aluminium) substrate. After laser treatment, samples are investigated with optical microscopy, profilometer and chemical analysis (FTIR & TGA). The results show that selective laser stripping is possible between different layers of external aircraft coatings and without any visual damage on the substrate material. In parallel to the experimental work, a numerical model has been developed to explain the background of the physical mechanisms and to qualitatively evaluate the detailed stress analysis and interfacial failure simulation for a single layer of epoxy on an aluminium substrate. The predicted failure patterns agree with the surfaces of the tested specimens observed by a microscope.

Isolation Experiments and Their Role in Risk Mitigation During Pandemics

The human is the most important element of the ecosystem. Due to the fact that the technosphere depends on the human life, the priority is to save the human health and to provide high performance even in stressful situations as it helps to mitigate risks when critical situations arise including at industries. In order to study the human behaviour under stress in more details, we suggest putting humans into the artificial ecosystem where the human is the key element. At this, the decomposition of such complex system is the external environment, the life support system arranges by technical means and the human acts as a loading element. Such approach should be applied to control the condition of the environment surrounding the human and to be able to model various scripts of the environmental effect on humans and vice versa. Such study has shown that human performance and general condition are affected by tiredness, the time spend in isolation, frequency of critical situations. The global situation in 2019-2020 and self-isolation during the pandemics allow expanding this study and evaluating the effect of isolation on the technosphere safety. The result of this work is the well-developed comprehensive human-machine system within which the study is carried out. Recommendations obtained during the calculation experiments are compared with the natural data. On these grounds, conclusions are drawn that allow one to mitigate risks under conditions of isolation.

Conflicts Factor and Stress Related to Health Problems of Official Employees

Objective: The objectives of this research were to 1) measure frequency of conflicts in the work detail,behavior, work relationship, and work stress, 2) study the relationship between conflicts in the organizationfactors of work detail, behavior, work relationship, and work stress, 3) analyze the work stress related tohealth problems, and 4) analyze the ability to explain the variation of conflicts in the organization on workdetail, behavior, work relationship, work stress toward health problems.Methods: The sample was 132 official employees collected by simple random sampling. The researchreferred to a quantitative technique that analyzed data using descriptive statistics, inferential statistics,Pearson’s product-moment correlation coefficient, chi-square, and multiple regression analysis.Results: The research proved that the majority often conflicted in work detail, behavior, work relationship,which their work relationship was an aspect that the respondents conflicted the most. The results revealedthat conflicts in work detail, behavior, and work relationship were related to work stress, which alsoaffected health problems. The variable of work stress can predict health problems accounted for 53%. Workrelationships can explain the variation of health problems estimated at 52% at the significance level of 0.05.Conclusion: This research can effectively implement conflict management and develop a good relationshipin the organization.

Research of microdeformation and stress in details of agricultural machines by implementing holography

The article presents theoretical and experimental studies of microstrains and stresses in the details of agricultural machines by the implementation of holography. The expansion of computer holography, associated with the development of optical methods for studying the technical condition of agricultural machinery and their components, is accompanied by significant complications associated with the interpretation of interferograms. An important solution was to investigate the process and the associated appearance of microdeformation fields on the surface of the product without destroying it. In this case, the conditions of the allowable load and, accordingly, the allowable technical condition of the product were created, when the natural sample or the real part was not destroyed, and the hologram was recorded at the time of appearance and development of microdeformations. The hologram reproduced the kinetics of the process in a three-dimensional image, where all the elements of the study were in real time and real size, which made it possible to capture the three components of the microdeformation vector. Such experimental researches for establishment of admissible values of a technical condition were carried out according to the developed technique were carried out for the first time. The use of holography as a means of research allowed to obtain the values of microdeformation in three directions of the vector, as well as to mathematically describe the dependence of these deformations on the coordinates.

Shortcut Method for “L” and “Z” Pipe Bend Sizing

Abstract In the engineering practice, it may often prove necessary to provide quick and relatively accurate estimates of piping routing and material requirements in very early stages of a project. In these cases, there is typically no time to perform detailed pipe stress analysis in order to obtain accurate routing, which allows for sufficient piping system flexibility, and the designer is constrained to the use of rule of thumb approach and good engineering judgment. This approach, although often used, may prove challenging in many situations, one of which is establishing sufficient pipe loop dimensions. Method proposed by the authors in Jacimovic and Ivosevic (2020, “Shortcut Method for Pipe Expansion Loop Sizing,” ASME J. Pressure Vessel Technol. 142(4), p. 041505) provides a procedure for quick estimation of U loops, while the present procedure aims to provide additional procedures for estimation of L and Z bends, thus completing the circle of shortcut methods for quick estimation of expansion requirements of piping systems.

Misorientation and grain boundary orientation dependent grain boundary response in polycrystalline plasticity

This paper studies the evolution of intergranular localization and stress concentration in three dimensional micron sized specimens through the Gurtin grain boundary model (J Mech Phys Solids 56:640–662, 2008) incorporated into a three dimensional higher-order strain gradient crystal plasticity framework (Yalcinkaya et al. in Int J Solids Struct 49:2625–2636, 2012). The study addresses continuum scale dislocation-grain boundary interactions where the effect of crystal orientation mismatch and grain boundary orientation are taken into account through the grain boundary model in polycrystalline metallic specimens. Due to the higher-order nature of the model, a mixed finite element formulation is used to discretize the problem in which both displacements and plastic slips are considered as primary variables. For the treatment of grain boundaries within the solution algorithm, an interface element is formulated and implemented together with the bulk plasticity model. The capabilities of the framework is demonstrated through 3D polycrystalline examples considering grain boundary conditions, grain boundary strength, the orientation distribution and the specimen size. A detailed grain boundary condition and stress concentration analysis is presented. The advantages and the disadvantages of the model is discussed in detail through numerical examples.

Size Effects of Brittle Particles in Aerosol Deposition\u2014Molecular Dynamics Simulation

Up to now, the role of particle sizes on the impact behavior of ceramic particles in aerosol deposition not yet fully understood. Hence, with the aim to supply a more general understanding, modeling series of low strain rate compression and high-speed impact were performed by molecular dynamics on single-crystalline particles in sizes of 10-300 nm that are tuned to match mechanical properties of TiO2-anatase. The modeling results reveal that particles with original diameter of 25-75 nm exhibit three different impact behaviors that could be distinguished as (i) rebounding, (ii) bonding and (iii) fragmentation, depending on their initial impact velocity. In contrast, particles larger than 75 nm do not exhibit the bonding behavior. Detailed stress and strain field distributions reveal that combination of “localized inelastic deformation” along the slip systems and “shear localization” cause bonding of the small and large particles to the substrate. The analyses of associated temperature rise by the inelastic deformation revealed that heat diffusion at these small scales depend on size. Whereas small particles could reach a rather homogeneous temperature distribution, the evolved heat in the larger ones keeps rather localized to areas of highest deformation and may support deformation and the formation of dense layers in aerosol deposition.

Low sun exposure habits is associated with a dose-dependent increased risk of hypertension: a report from the large MISS cohort

In prospective observational cohort studies, increasing sun exposure habits have been associated with reduced risk of cardiovascular mortality. Our aim was to assess possible observational mechanisms for this phenomenon. A written questionnaire was answered by 23,593 women in the year 2000 regarding risk factors for melanoma, including factors of possible interest for hypertension, such as detailed sun exposure habits, hypertension, marital status, education, smoking, alcohol consumption, BMI, exercise, and chronic high stress. Hypertension was measured by the proxy “use of hypertension medication” 2005–2007, and high stress by “need of anti-depressive medication”. Sun exposure habits was assessed by the number of `yes’ to the following questions; Do you sunbath during summer?, During winter vacation?, Do you travel south to sunbath?, Or do you use sun bed? Women answering ‘yes’ on one or two questions had moderate and those answering ‘yes’ on three or four as having greatest sun exposure. The main outcome was the risk of hypertension by sun exposure habits adjusted for confounding. As compared to those women with the greatest sun exposure, women with low and moderate sun exposure were at 41% and 15% higher odds of hypertension (OR 1.41, 95% CI 1.3‒1.6, p < 0.001 and OR 1.15, 95% CI 1.1‒1.2, p < 0.001), respectively. There was a strong age-related increased risk of hypertension. Other risk factors for hypertension were lack of exercise (OR 1.36), a non-fair phenotype (OR 1.08), chronic high stress level (OR 1.8), and lack of university education (OR 1.3). We conclude that in our observational design sun exposure was associated with a dose-dependent reduced risk of hypertension, which might partly explain the fewer deaths of cardiovascular disease with increasing sun exposure.

Mass Spring Models of Amorphous Solids

In this paper we analyse static properties of mass spring models (MSMs) with the focus of modelling non crystalline materials, and explore basic improvements, which can be made to MSMs with disordered point placement. Presented techniques address the problem of high variance of MSM properties which occur due to randomised nature of point distribution. The focus is placed on tuning spring parameters in a way which would compensate for local non-uniformity of point and spring density. We demonstrate that a simple force balancing algorithm can improve properties of the MSM on a global scale, while a more detailed stress distribution analysis is needed to achieve local scale improvements. Considered MSMs are three dimensional.

Voxel-based finite element modelling of wood elements based on spatial density and geometry data using computed tomography

Abstract In this paper, voxel-based finite element modelling based on spatial geometry and density data is applied to simulate the detailed stress and strain distribution in a large wood element. As example, a moulded wooden tube with a length of 3 m and a diameter of 0.3 m is examined. Gamma-ray computed tomography is used to obtain both, its actual geometric shape and spatial density distribution. Correlation functions (R2 ≈ 0.6) between density and elastic material properties are experimentally determined and serve as link for defining the non-uniform distribution of the material properties in the finite element model. Considering the geometric imperfections and spatial variation of the material properties, a detailed analysis of the stress and strain distribution of a wood element is performed. Additionally, a non-destructive axial compression test is applied on the wooden tube to analyse the load-bearing behaviour. By means of digital image correlation, the deformation of the surface is obtained, which also serves for validation of the finite element model in terms of strain distributions.

ASSESSMENT OF ROLLING BEARINGS OPERATING CONDITIONS

The article examines the possibilities of ensuring the reliability of the rolling bearingsof the equipment used in the process of painting aluminum sheets. It was noted that the fully mechanized production line at the enterprise ensures the pro-duction of high quality aluminum sheets. However, the productivity of the technological equipment usedin the dyeing process and the rejection of the bearings have a negative impact on the efficiency of production. Technological machines and equipment work in Azeraluminum OJSC in particularly difficult conditions, and therefore there is a need to increasethe reliability and longevity of the used roller bearings. The operating conditions of the bearingss, the distribution of loads between the rolling elements, as well as the contact stresses in the bearings details were assessed.

Trap-dominated nitrogen dioxide and ammonia responses of air-stable p-channel conjugated polymers from detailed bias stress analysis

Trap and carrier density modulation via bias stress is a determining factor in OFET responses to analyte vapors. The interplay between vapor exposure and bias stress influences signal strength from polymer-based OFET sensors.

The Evolution from Life Insurance to Financial Engineering

Since the mid-1980s, the share of household net worth intermediated by US financial institutions has shifted from defined benefit plans to life insurers and defined contribution plans. Life insurers have primarily grown through variable annuities, which are mutual funds with longevity insurance, a potential tax advantage, and minimum return guarantees. The minimum return guarantees change the primary function of life insurers from traditional insurance to financial engineering. Variable annuity insurers are exposed to interest and equity risk mismatch and their stock returns were especially low during the COVID-19 crisis. We consider regulatory changes, such as more detailed financial disclosure and standardized stress tests, to monitor potential risk mismatch and to ensure stability of the insurance sector.

Paper] Multimodal Stress Estimation Using Multibiological Information: Towards More Accurate and Detailed Stress Estimation

Paper] Multimodal Stress Estimation Using Multibiological Information: Towards More Accurate and Detailed Stress Estimation

Optimization Analysis Method of New Orthotropic Steel Deck Based on Backpropagation Neural Network‐Simulated Annealing Algorithm

To study the effects of the fatigue performance due to the major design parameter of the orthotropic steel deck and to obtain a better design parameter, a construction parameter optimization method based on a backpropagation neural network (BPNN) and simulated annealing (SA) algorithm was proposed. First, the finite element (FE) model was established, and the numerical results were validated against available full‐scale fatigue experimental data. Then, by calculating the influence surface of each fatigue detail, the most unfavorable loading position of each fatigue detail was obtained. After that, combined with the data from actual engineering applications, the weight coefficient of each fatigue detail was calculated by an analytic hierarchy process (AHP). Finally, to minimize the comprehensive stress amplitude, a BPNN and SA algorithm were used to optimize the construction parameters, and the optimization results for the conventional weight coefficients were compared with the construction parameters. It can be concluded that compared with the FE method through single‐parameter optimization, the BPNN and SA method can synthetically optimize multiple parameters. In addition, compared with the common weighting coefficients, the weighting coefficients proposed in this paper can be better optimized for vulnerable parts. The optimized fatigue detail stress amplitude is minimized, and the optimization results are reliable. For these reasons, the parameter optimization method presented in this paper can be used for other similar applications.