For a type IV hydrogen storage vessel, the complexity of the mechanical system is a result of the increased number of thin-layered composites and geometrical details at dome parts, which ...significantly prolongs the computation time for traditional numerical analysis and optimal design. In this work, a framework couples machine learning (ML) and finite element (FE) analysis is proposed for a 70 MPa type IV vessel. Providing an approach that allows the winding parameters optimization process to include the corresponded feasible dome geometry. High-fidelity FE models are established and different failure modes are included. The artificial neural network (ANN) is developed and coupled with the FE models, where the irregularity of directional material distribution on both cylindrical and dome regions is adequately considered during the optimization process. Winding parameters extended by practical production modifications such as transition areas and layer ending adjustments are introduced to the modified input layer of ANN, to ensure the integrality of the complex geometrical details. The computational cost is greatly reduced with satisfying accuracy compared to FE analysis, where the optimized lay-up scheme could be obtained with a prediction error of less than 2% on the damage state function. The associated simulation results show an obvious improvement in mechanical response under designed burst pressure. Particularly, the prototypical vessels are further produced to carry out comparative experiments, which indicate that the burst pressure of the type IV vessel has been improved from 145 MPa to 157.74 MPa. This is also consistent with the numerical prediction of burst pressure using Hashin failure criteria and progressive damage analysis.
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•ANN-based machine learning (ML) algorithms is used to optimize 70 MPa type IV vessel.•The irregularity of directional material distribution in dome regions is well considered.•Transition areas and layer-ending adjustments are introduced to the modified input layer of ANN.•Multiple failure modes and mechanical performances are considered to evaluate the outputs.
Summary
In this study, a new adaptive method for crack propagation analysis is developed by using the material point method coupled with a phase‐field fracture model for brittle materials. A ...background grid of material particles is adaptively refined based on the amount of material damage to resolve the length scale in the phase‐field evolution equation. A division process of the material particles associated with the refined background cells is also performed to increase the resolution of solutions near the crack tip. The effectiveness and validity of the proposed method is assessed through several numerical examples for crack propagation in brittle materials.
The paper investigates the cyclic response of soft cellular materials undergoing repeated local instabilities. Our focus is mainly on the coupling between material non-linearities, geometric ...non-linearity as well as defects induced by 3D printing. Two paradigmatic lattices (triangular and hexagonal), each with its own distinct deformation mode and defect sensitivity, are examined, and the emergence of as-built material and geometric defects in the form of microporosity, strut thickness reduction, and nodal dispersion is studied via computed tomography and optical analyses. Experiments are carried out on the base material and lattice specimens for given cycling strains and cycle ratios. Numerical models are developed to understand the individual role of the main constitutive aspects of the base material, e.g. damage, creep, and visco-elasticity, as well as to assess the role of defects in each architecture. The results show that the activation of local buckling combined with the engagement of material non-linearities has multiple outcomes. It leads to local storage of inelastic strain, which in turn perturbs the lattice geometry after the second cycle and severely impacts the subsequent response, e.g. softening; it reduces the tangent modulus at zero strain; and it also decreases the maximum and minimum cyclic stresses. The detriment is further fueled by geometric deviations caused by 3D printing. Furthermore, a theoretical model is presented to obtain stress bound estimates of the stabilized response, hence offering guidelines for the design of 3D printed soft metamaterials under cycling loading. The paper concludes with a systematic discussion on the coupled role of non-linearities (material and geometry) and defects, and on the accuracy of the numerical and theoretical models herein presented.
•The cyclic engagement of elastic instability is investigated in elastomeric lattices.•The role of as-built material and geometric defects in the cyclic response is quantified.•The interaction between defects, material and geometric non-linearity is unveiled.•A theoretical model is presented to predict stress bounds of the stabilized response.
Superstructures are seriously damaged because of plastic deformation when natural disasters, such as large earthquakes or unexpectedly large waves, occur. Therefore, there is a need to develop ...materials that are resistant to damage and fracture while maintaining a certain level of strength. In this paper, the difference in material toughness changes when cyclic prestrain occurs among different ferrite/pearlite two-phase microstructures were investigated. Synthetic analysis using strain gradient plasticity (SGP) theory, one of the crystal plasticity theories, was carried out, and conventional macroscopic material damage consideration rules were employed. Then, it was suggested that the amount of material damage changes among the different microstructures. In addition, a parametric study using SGP theory is performed to suggest directions for the microstructural design of steel with a lower risk of brittle fracture due to plastic deformation. As a result, damage-resistant materials with sufficient strength can be proposed.
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•Dependency of microstructure on material damage due to prestrain is discovered.•Material damage due to prestrain can be estimated by dislocation density.•Material damage due to prestrain decreases with interconnected hard phase.
The lockdowns that came with policies to reduce the spread of COVID-19 in 2020 required some 90% of museums and historic properties across the globe to be closed. Lowered visitor numbers and reduced ...staffing levels allowed a range of fauna to make their way indoors, bringing an increase in birds, rodents and insect pests. Silverfish are shy, so benefit from low occupancy in museums and present a potential vector for damage to books and paper. This study is the first to report changes in insect populations in museums and examines six years (2015–2020) trapping data for silverfish and similar insects (Lepismatidae): Lepisma saccharinum, Ctenolepisma calvum, Ctenolepisma longicaudatum and Ctenolepisma lineatum from: (i) the Technisches Museum Wien, (ii) Schönbrunn Palace, (iii) Hofburg Museum and a shorter record from (iv) Weltmuseum Wien. Analysis of the trap contents gives an impression that the number of insects caught had increased over time, but 2020 was distinctive and gave typically higher insect numbers during the COVID-19 lockdown compared to other years, especially for Lepisma saccharinum. Individual traps caught up to 100 silverfish in only a few weeks. Because silverfish usually need between four months to one year to become mature, we assume that it was increased activity during museum closure and not higher reproduction which led to higher numbers. The parts of the museums showing increased populations under lockdown were similar to the areas where they were more frequent in earlier years. This means that such areas deserve continued monitoring even when the museum is closed. No damage to paper objects were reported in the museums investigated.
•Silverfish trapped have generally increased over the years 2015–2020.•During museum closures silverfish increased in places typically seen as habitats.•Increased trapping arose because silverfish could range widely in unoccupied museums.
Prema odredbi čl. 19. ZOO/05 svaka fizička i pravna osoba ima pravo na zaštitu svojih prava osobnosti pod pretpostavkama utvrđenim zakonom, a pod pravima osobnosti razumijevaju se pravo na život, ...tjelesno i duševno zdravlje, ugled, čast, dostojanstvo, ime, privatnost osobnog i obiteljskog života, sloboda i dr. Odredbom čl. 1046. ZOO/05 neimovinska šteta definirana je kao povreda prava osobnosti, a odredbom čl. 1100. ZOO/05 propisano je da će sud, ako težina povrede i okolnosti slučaja to opravdaju, dosuditi novčanu naknadu zbog povrede prava osobnosti, vodeći pri tome računa o dužini i jačini pretrpljenih duševnih i fizičkih boli, straha te svrsi kojoj naknada služi. Iako ZOO/05 uvodi u naš pravni sustav objektivnu koncepciju neimovinske štete u smislu da je pravno priznata neimovinska šteta ona tzv. primarna šteta koja nastaje samom povredom zaštićenog neimovinskog dobra, sudska praksa pokazuje kako su u procjeni postojanja neimovinske štete i nadalje odlučne činjenice koje tvore subjektivni koncept neimovinske štete, tj. takozvana sekundarna šteta u vidu jačine i trajanja fizičkih i duševnih boli te straha. Navedeno je potvrđeno zauzetim pravnim shvaćanjem Građanskog odjela Vrhovnog suda Republike Hrvatske od 5. ožujka 2020. i 15. lipnja 2020. godine, kojim Vrhovni sud RH daje do znanja da su i nadalje u primjeni Orijentacijski kriteriji i iznosi za utvrđivanje visine pravične novčane naknade nematerijalne štete VSRH od 29. studenog 2002., koji su doneseni za primjenu subjektivnog koncepta neimovinske štete iz čl. 200. ZOO/91, smatrajući da su podobni i za primjenu odredaba čl. 19., 1046. te čl. 1100. ZOO/05. Orijentacijski kriteriji za neimovinsku štetu Vrhovnog suda RH tijekom vremena sve su više izloženi kritici u smislu da je promjena koncepta poimanja neimovinske štete trebala i/ili morala dovesti i do suštinske promjene u činjeničnoj i pravnoj osnovi zahtjeva kojim se potražuje naknada neimovinske štete. Osobito se ta problematika potencira u slučajevima kada se pojavi dilema je li štetnom radnjom došlo do povrede većeg broja prava osobnosti ili je uvijek riječ o jednom pravu osobnosti, odnosno u slučajevima kada povredu prava osobnosti nije moguće iskazati kroz odredbu stavka 2. čl. 1100. ZOO/05 zato što se nije manifestirala kao fizička i duševna bol, odnosno strah, pa nije moguće primijeniti Orijentacijske kriterije VSRH. Ovim radom pokušat će se analizirati na koji bi način trebalo odrediti činjeničnu i pravnu osnovu tužbenog zahtjeva, odnosno kako postaviti tužbeni zahtjev u slučajevima kada jedna štetna radnja izazove veći broj povreda prava osobnosti, odnosno kada je riječ o povredi prava osobnosti koju po svojoj naravi nije moguće procijeniti s pomoću stavka 2. čl. 1100. ZOO-a, odnosno nije moguće primijeniti Orijentacijske kriterije VSRH za neimovinsku štetu.
The microprocess of brittle fracture in steel is suggested to occur because microcracks appearing in the brittle layer at the grain boundary propagate driven by increased piled-up dislocation. Thus, ...loading plastic deformation, equivalent to the increase in dislocation, is directly connected to the increase in brittle fracture risk. Because of these mechanisms, prestraining means approaching the limits of the material, which could lead to deterioration of fracture toughness. For a lifetime evaluation of steel structure, it is important to generalize the effect of various cyclic prestrains.
In this paper, material toughness changes when tensile and compression prestrain occur were investigated. A general three-point bending test was employed to evaluate fracture. Synthetic analysis using Conventional Mechanism-based Strain Gradient Plasticity (CMSGP) theory, in which dislocation density is used to determine the amount of material damage, was carried out as well as employing conventional macroscopic material damage consideration rules. The consistency of the simulation and the experimental results were supported by the Electron Back Scattered Diffraction Pattern (EBSD) observation. Additionally, critical stress was calculated, and the change in critical stress for prestrain conditions was investigated. Then, the mechanism of critical stress changes could be expressed by the yield point increase and dislocation density.
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•Dependency of pre-strain order on material damage is discovered.•Material damage can be estimated by back stress uploading and dislocation density.•Critical stress changes dependent on dislocation density and yield point change.
Constitutive equations for inelastic behavior of anisotropic materials have been a challenge for decades. Presented is a new spherocylindrical microplane constitutive model that meets this challenge ...for the inelastic fracturing behavior of orthotropic materials, and particularly the shale, which is transversely isotropic and is important for hydraulic fracturing (aka fracking) as well as many geotechnical structures. The basic idea is to couple a cylindrical microplane system to the classical spherical microplane system. Each system is subjected to the same strain tensor while their stress tensors are superposed. The spherical phase is similar to the previous microplane models for concrete and isotropic rock. The integration of stresses over spherical microplanes of all spatial orientations relies on the previously developed optimal Gaussian integration over a spherical surface. The cylindrical phase, which is what creates the transverse isotropy, involves only microplanes that are normal to plane of isotropy, or the bedding layers, and enhance the stiffness and strength in that plane. Unlike all the microplane models except the spectral one, the present one can reproduce all the five independent elastic constants of transversely isotropic shales. Vice versa, from these constants, one can easily calculate all the microplane elastic moduli, which are all positive if the elastic in-to-out-of plane moduli ratio is not too big (usually less than 3.75, which applies to all shales). Oriented micro-crack openings, frictional micro-slips and bedding plane behavior can be modeled more intuitively than with the spectral approach. Data fitting shows that the microplane resistance depends on the angle with the bedding layers non-monotonically, and compressive resistance reaches a minimum at 60°. A robust algorithm for explicit step-by-step structural analysis is formulated. Like all microplane models, there are many material parameters, but they can be identified sequentially. Finally, comparisons with extensive test data for shale validate the model.
Delamination is a common defect in carbon fiber reinforced polymer (CFRP) during the molding process. Accurately understanding the formation and evolution mechanisms of drilling damage in CFRP with ...delamination defects is helpful for effectively suppressing drilling defects with delamination. In this study, a macro-micro finite element model (FEM) of CFRP with prefabricated delamination defects during drilling is established to simulate and analyze the damage formation and evolution behavior. The circular polytetrafluoroethylene (PTFE) films are employed to simulate the delamination defects in CFRP. These samples with different sizes of prefabricated delamination defects are prepared for the drilling experiments. The results show that the maximum errors of the thrust force and the exit damage factor between the simulation and experiments are 8.75% and 4.2% respectively, indicating good reliability of the simulation model. Under the condition of CFRP with delamination defects, as the size of the delamination defects increases, the maximum thrust force decreases, while the maximum delamination propagation length and exit damage increase. Compared to the case without delamination defects, when the delamination diameter is 7 mm, the delamination propagation percentage and the maximum stress in CFRP increase by 52.17% and 155.4% respectively, and the maximum increment of the exit delamination damage factor is 38%.
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