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Structural Topology Optimization typically features continuum-based descriptions of the investigated systems. In Part 1 we have proposed a Topology Optimization method for discrete systems and tested it on quasi-static 2D problems of stiffness maximization, assuming linear elastic material. However, discrete descriptions become particularly convenient in the failure and post-failure regimes, where discontinuous processes take place, such as fracture, fragmentation, and collapse. Here we take a first step towards failure problems, testing Discrete Element Topology Optimization for systems with nonlinear material responses. The incorporation of material nonlinearity does not require any change to the optimization method, only using appropriately rich interaction potentials between the discrete elements. Three simple problems are analysed, to show how various combinations of material nonlinearity in tension and compression can impact the optimum geometries. We also quantify the strength loss when a structure is optimized assuming a certain material behavior, but then the material behaves differently in the actual structure. For the systems considered here, assuming weakest material during optimization produces the most robust structures against incorrect assumptions on material behavior. Such incorrect assumptions, instead, are shown to have minor impact on the serviceability of the optimized structures.

Structural Topology optimization is attracting increasing attention as a complement to additive manufacturing techniques. The optimization algorithms usually employ continuum-based Finite Element analyses, but some important materials and processes are better described by discrete models, for example granular materials, powder-based 3D printing, or structural collapse. To address these systems, we adapt the established framework of SIMP Topology optimization to address a system modelled with the Discrete Element Method. We consider a typical problem of stiffness maximization for which we define objective function and related sensitivity for the Discrete Element framework. The method is validated for simply supported beams discretized as interacting particles, whose predicted optimum solutions match those from a classical continuum-based algorithm. A parametric study then highlights the effects of mesh dependence and filtering. An advantage of the Discrete Element Method is that geometric nonlinearity is captured without additional complexity; this is illustrated when changing the beam supports from rollers to hinges, which indeed generates different optimum structures. The proposed Discrete Element Topology Optimization method enables future incorporation of nonlinear interactions, as well as discontinuous processes such as during fracture or collapse.

The internal structure and mechanics of the fibre materials, such as yarn or woven textile, are highly complex. Exploring the fibre structure is an essential step in material engineering either from the experimental or computational point of view. In this study, a new method to extract geometrical and morphological parameters of fibre structures is proposed. The method benefits from standard image analysis and machine learning technique to efficiently extract fibre segments from microcomputer tomography data. The proposed algorithm is tested on the yarn and woven textile materials with different resolution and quality. The developed method can extract the individual fibres with varying accuracy from 73-100% with processing time 2-5s on the tested samples.

A surface mesh represented discrete element method (SMR-DEM) for granular systems with arbitrarily shaped particles is presented. The particle surfaces are approximated using contact nodes obtained from surface mesh. A hybrid contact method which combines the benefits of the sphere-to-sphere and sphere-to-surface approaches is proposed for contact detection and force computation. The simple formulation and implementation render SMR-DEM suitable for three-dimensional simulations. Furthermore, GPU parallelization is employed to achieve higher efficiency. Several numerical examples are presented to show the performance of SMR-DEM. It is found that on the particle level the method is accurate and convergent, while on the system level SMR-DEM can effectively model particle assemblies of various regular and complex irregular shapes.

This research proposes a low-cost and simple operation microfluidic chip to enhance the magnetic labeling efficiency of two ischemic stroke biomarkers: cellular fibronectin (c-Fn) and matrix metallopeptidase-9 (MMP9). This fully portable and pump-free microfluidic chip is operated based on capillary attractions without any external power source and battery. It uses an integrated cellulose sponge to absorb the samples. At the same time, a magnetic field is aligned to hold the target labeled by the magnetic nanoparticles (MNPs) in the pre-concentrated chamber. By using this approach, the specific targets are labeled from the beginning of the sampling process without preliminary sample purification. The proposed study enhanced the labeling efficiency from 1 hr to 15 min. The dynamic interactions occur in the serpentine channel, while the crescent formation of MNPs in the pre-concentrated chamber, acting as a magnetic filter, improves the biomarker-MNP interaction. The labeling optimization by the proposed device influences the dynamic range by optimizing the MNP ratio to fit the linear range across the clinical cutoff value. The limit of detection (LOD) of 2.8 ng/mL and 54.6 ng/mL of c-Fn measurement were achieved for undiluted and four times dilutions of MNP, respectively. While for MMP9, the LODs were 11.5 ng/mL for undiluted functionalized MNP and 132 ng/mL for four times dilutions of functionalized MNP. The results highlight the potential use of this device for clinical sample preparation and specific magnetic target labeling. When combined with a detection system could also be used as an integrated component of a point-of-care platform.

This study covers an extended spectrum of clinical cases (1) to analyze the accurate tumour size, (2) to demarcate accurate tumour boundaries in order to plan an effective target volumes for radiotherapy, thermal ablation including radiofrequency ablation and nanoparticles induced thermal ablation. Once the clinical size of the tumour is established, realistic three-dimensional volume of the tumour can be calculated. Accurate margins (0.5 cm -1 cm) can only be sacrificed if true tumour boundaries with irregular nodal spread can be retrieved.

With availability of high power ultra short pulsed lasers, one prerequisite towards throughput scaling demanded for industrial ultrafast laser processing was recently achieved. We will present different scaling approaches for ultrafast machining, including raster and vector based concepts. The main attention is on beam shaping for enlarged, tailored processed volume per pulse. Some aspects on vector based machining using beam shaping are discussed. With engraving of steel and full thickness modification of transparent materials, two different approaches for throughput scaling by confined interaction volume, avoiding detrimental heat accumulation, are exemplified. In Contrast, welding of transparent materials based on nonlinear absorption benefits from ultra short pulse processing in heat accumulation regime. Results on in-situ stress birefringence microscopy demonstrate the complex interplay of processing parameters on heat accumulation. With respect to process development, the potential of in-in-situ diagnostics, extended to high power ultrafast lasers and diagnostics allowing for multi-scale resolution in space and time is addressed.

The design of structures using topology optimization can improve the structural performance and save material, in turn reducing costs. Using a framework of large-scale, three-dimensional topology optimization implemented by the authors in an open-source multiphysical software, we investigate the influence of uncertain loading on the optimized design. Direct differentiation is used to reveal the relationship between displacements and applied force, giving an efficient and effective tool to postprocess optimized topologies. The developed methodology for the assessment of the sensitivity with respect to applied forces is explored using two three-dimensional examples: the classic MBB cantilever and a cableway pylon. The advantages and limitations of this method are discussed.

Generalized-α time integration is a generalization of several time integration schemes that can be use in the analysis of dynamic systems. Sensitivity analysis is used in numerical methods of design optimization, uncertainty analysis, parameter fitting and for simply calculating the sensitivities of a design to certain parameters. Analytical sensitivity analysis reduces the computational effort compared with numerical analysis and is therefore essential in efficient gradient-based design optimization. In this study, the sensitivity equations of the generalized-α time integration via direct differentiation are introduced. These are then compared with numerical sensitivities via forward differencing and Newmark-β in terms of accuracy and performance. An example is shown for both linear structural dynamics and flexible multibody dynamics.

Use of Metal and its alloys have become the need of this world. high strength pipes and equipment are required for the extraction of bituminous oil from soil. For this High strength Low Alloy Steel (Micro-alloyed steels) can be used. HSLA required large size ingots for its manufacturing therefore in recent years, large size ingots demand is increased. Large size ingots are subjected to cracking while manufacturing during open die forging process. Optical Scanning Electron Microscopies and Energy dispersion Spectroscopy techniques are carried out for the investigation of root causes of the cracking during forging of large size ingots. Microstructure of large size ingots sample are reviewed at different locations and grain boundaries. Results of these chemical techniques shows the enrichment of chromium and oxygen content at the boundaries which clearly differentiated a cracked boundary and non-cracked locations. This writing comprises the literature study, test procedures and analyzing the results to review that abnormal grain growth was the cause of cracking of large size ingots during forging process. The report also reviewed, alternate heat treatments and possible solution.

The present decade has witnessed a huge volume of research revolving around a number of Additive Manufacturing (AM) techniques, especially for the fabrication of different metallic materials. How- ever, fabrication of ceramics and cermets using AM-based techniques mainly suffers from two primary limi- tations which are: (i) low density and (ii) poor mechanical properties of the final components. Although there has been a considerable volume of work on AM based techniques for manufacturing ceramic and cermet parts with enhanced densities and improved mechanical properties, however, there is limited understanding on the cor- relation of microstructure of AM-based ceramic and cermet components with the mechanical properties. The present article is aimed to review some of the most commonly used AM techniques for the fabrication of ceramics and cermets. This has been followed by a brief discussion on the microstructural developments during different AM-based techniques. In addition, an overview of the challenges and future perspectives, mainly associated with the necessity towards developing a systematic structure-property correlation in these materials has been provided based on three factors viz. the efficiency of different AM-based fabrication techniques (involved in ceramic and cermet research), an interdisciplinary research combining ceramic research with microstructural engineering and commercialisation of different AM techniques based on the authors’ viewpoints.

Nowadays, one of the global problems is climate change. Commercial and residential buildings are among the most powerful consumers of energy. The energy consumption of buildings increases because of the development of the residents’ needs. Zero Energy Building uses renewable energy sources therefore Zero Energy Buildings have advantages in the field of environmental care because of the mitigation of CO2 emissions and the decrease of energy use in the building sector. The deposits of fossil fuel deplete at a high rate. The new deposits are extremely hard to find and if they are discovered are smaller than already used ones. Therefore, Zero Energy Buildings are the solution for this problem because they do not depend on fuel.

Nano-filled polymers are becoming more and more important to meet the continuously growing requirements of modern engineering problems. The investigation of these composite materials at the molecular level, however, is either prohibitively expensive or just impossible. Multiscale approaches offer an elegant way to analyze such nanocomposites by significantly reducing computational costs compared to fully molecular simulations.When coupling different time and length scales, however, it is in particular important to ensure that the same material description is applied at each level of resolution.The Capriccio method, for instance, couples a particle domain modeled with molecular dynamics (MD) with a finite element based continuum description and has been used i.a. to investigate the effects of nano-sized silica additives embedded in atactic polystyrene (PS). However, a simple hyperelastic constitutive law is used so far for the continuum description which is not capable to fully match the behavior of the particle domain. To overcome this issue and to enable further optimization of the coupling scheme, the material model used for the continuum should be derived directly from pure MD simulations under thermodynamic conditions identical to those used by the Capriccio method.To this end, we analyze the material response of pure PS under uniaxial deformation using strain-controlled MD simulations. Analogously, we perform simulations under pure shear deformation to obtain a comprehensive understanding of the material behavior.As a result, the present PS shows viscoelastic characteristics for small strains, whereas viscoplasticity is observed for larger deformations. The insights gained and data generated are used to select a suitable material model whose parameters have to be identified in a subsequent parameter optimization.

This contribution introduces an unconventional procedure to characterize spatial profiles of elastic and inelastic properties inside polymer interphases around nanoparticles. Interphases denote those regions in the polymer matrix whose mechanical properties are influenced by the filler surfaces and thus deviate from the bulk properties. They are of particular relevance in case of nano-sized filler particles with a comparatively large surface-to-volume ratio and hence can explain the frequent observation that the overall properties of polymer nanocomposites cannot be determined by classical mixing rules, which only consider the behavior of the individual constituents. Interphase characterization for nanocomposites poses hardly solvable challenges to the experimenter and is still an unsolved problem in many cases. Instead of real experiments, we perform pseudo experiments using our recently developed Capriccio method, which is an MD-FE domain-decomposition tool specifically designed for amorphous polymers. These pseudo-experimental data then serve as input for a typical inverse parameter identification. With this procedure, spatially varying mechanical properties inside the polymer are, for the first time, translated into intuitively understandable profiles of continuum mechanical parameters. As a model material, we employ silica-enforced polystyrene, for which our procedure reveals exponential saturation profiles for Young’s modulus and the yield stress inside the interphase, where the former takes about seven times the bulk value at the particle surface and the latter roughly triples. Interestingly, hardening coefficient and Poisson’s ratio of the polymer remain nearly constant inside the interphase. Besides gaining insight into the constitutive influence of filler particles, these unexpected and intriguing results also offer interesting explanatory options for the failure behavior of polymer nanocomposites.

This paper presents a novel class of (space)time-modulated metasurfaces, namely (space)time metasurfaces that are modulated by pseudo-random sequence (PRS) waveforms. In contrast to their harmonically or quasi-harmonically modulated counterparts, these metasurfaces massively alter the temporal spectrum of the waves that they process; as a result, they exhibit distinct properties and offer complementary applications. These metasurfaces are assumed here to operate in the `slow-modulation' regime, where the fixed-state time between state-transition is much larger than the transient time associated with the dispersion of the media involved, which allows safe separation of the time-variance and frequency-dispersive effects of the system. Thanks to the special properties of their modulation, which are generally assumed to have a staircase shape and to be periodic in addition to being pseudo-random, the PRS (space)time-modulated metasurfaces can perform a number of unique operations, such as spectrum spreading, interference suppression, and row/cell selection. These properties, combined with modern microwave CMOS technologies, lead to applications with unique performance or/and features, such as electromagnetic stealth, secured communication, direction of arrival estimation, and spatial multiplexing.

The application of machine learning in the field of materials engineering can facilitate materials design and enable faster discovery of novel materials. This paper presents a deep learning approach for the prediction of the transverse elastic and plastic properties of unidirectional fibre reinforced composites directly from images of their microstructures. The training dataset consists of finite element predictions of the elastic-plastic properties of a set of 2D representative volume elements of unidirectional composites with different volume fraction and fiber diameter. Single-regression, Fully-connected Neural Networks (FcNNs) and a multi-regression Convolutional Neural Network (CNN) are designed and trained to predict 5 mechanical properties, using as input the images of the material’s microstructure. The performance of the FcNNs and of the CNN are compared; the CNN is shown to perform the most effective regression, predicting the properties of the composites with an accuracy of 99%. A key value addition in this research lies in the explainability of the otherwise ‘blackbox’ CNN model, guiding the reader through the model’s predictive process. We test the CNN on real, relatively low-resolution micrographs of composite microstructures and we find that this provides accurate predictions.

This work is mainly focused on studying the sensitivity of changing the optical and thermal physical parameters of the Parabolic Trough Collector receiver unit and their corresponding impact on the thermal and optical performances, such as the thermal distribution of the heat transfer fluid along the length, the thermal distribution of both the absorber pipe and the outer cover of the receiver along the circumference and related efficiencies. In this paper, novel experimental results of a receiver unit operating with an IR reflective mirror material inside the receiver are introduced. Besides, novel aspects of the background theory for the reviver unit related to IR reflectivity in the receiver annulus are discussed and implemented in a simulation code. A comparison between a developed model and simulation results is conducted.

Data transmission back and forth between finite element analysis (FEA) and computer-aided design (CAD) is a matter of huge concern today [2] and Isogeometric analysis [1] has been successful in merging these two fields in the recent past. The presentation will address isogeometric finite element approach (IGA) in combination with the first-order deformation plate theory (FSDT) for thermal buckling analysis of laminated composite plates. The IGA utilizes non-uniform rational B-spline (NURBS) as basis functions, resulting in both exact geometric representation and high order approximations [3] [4]. It enables to achieve easily the smoothness with arbitrary continuous order. The analyses have been performed using Bezier extraction and conventional IGA. In conventional isogeometric analysis the basis functions are not confined to one single element, but span a global domain whereas the Bézier extraction operator decomposes a set of linear combinations of Bernstein polynomials. The presentation will give a theoretical overview of B-splines, as well as NURBS, and also the concept of Bézier decomposition of these spline functions. The focus will then be on how the use of Bézier extraction eased the implementation into an already existing finite element code. This theoretical background will then be used to explain an isogeometric finite element analysis program. With the advent of More Electric Aircrafts [5], solving thermal structural problems [6] are of utmost importance in the aerospace industry. A static thermal structural validation problem will be presented for both constant and linear thermal temperature variation along the thickness. The presentation will then explain the procedures implemented for stress recovery and computing the geometric stiffness matrix. Numerical results of circular and elliptical plates will be provided to validate the effectiveness of the proposed method as compared to traditional FEA. The final section of the presentation proposes to detail the influences of length to thickness ratio, aspect ratio, boundary conditions, stacking sequence and material property on the critical buckling temperature. A special section would cover the idea of third order deformation theory for thicker plates and the effect of degree of NURBS basis on the results.

The main focus of this work is to investigate and compare the effect of adding nanoparticles to composite laminates on fracture process zone characterization including bridging and cohesive laws according to a multistage traction-separation law. To do this, three different methods have been utilized (Corrected Beam Theory, Experimental Compliance Method and Modified Compliance Calibration) to calculate the energy release rates in Mode I fracture. The numerical investigation of mode I fracture in nanocomposite laminates was done based on the multistage traction-separation law derived from double cantilever beam tests.

This paper presents the results of studies of the process of refining the pulp in a refiner with the influence of freeness of wood fibers after the defibrator on the physicomechanical properties of the fiberboards.

The burgeoning need to sequester anthropogenic CO_2 for climate mitigation and the need for energy sustenance leading upto enhanced geothermal energy production has made it incredibly critical to study potential earthquakes due to fluid activity in the subsurface. These earthquakes result from reactivation of faults in the subsurface due to pore pressure perturbations. In this work, we provide a framework to model fault slip due to pore pressure change leading upto quantifying the earthquake magnitude.

In this paper, we have studied the hypervelocity expansion of a spherical cavity in an infinite medium modeled with theextension of the porous plasticity criterion of Gurson [23] developed by Chen and Yuan [7] to account for plastic strain gradient induced size effects. Following the self-similar, steady-state solution derived by Cohen and Durban [9] for size-independent porous materials, we have computed the critical cavity expansion velocity which leads to the emergence of plastic shock waves for a wide range of initial void volume fractions and different values of the length scale parameter that controls the effect of size. We have shown that size effects hinder the emergence of plastic shock waves, so that as the length scale parameter increases, the expansion velocity required for the plastic shock to be formed increases. In addition, while porosity favors the formation of plastic shocks, as shown by Cohen and Durban [9], our results indicate that the effect of initial void volume fraction on plastic shock wave formation decreases for size-dependent materials.

In an earlier work, we introduced the two-grid method for unstructured tetrahedra applied to staggered solution of coupled flow and poromechanics and demonstrated its accuracy for the benchmark Mandel’s problem. In this work, we employ the two-grid method to study surface deformation and fault stability in a field scale carbon storage project.

Bistable fully closed shells can serve as long supporting structures that can be folded into a compact transport geometry and unfolded at the construction place. Bistability is achieved by introducing a specific distribution of residual stresses through the thickness of the shell, e.g. by incremental die-bending. In order to find a suitable bending radii combination a semi-analytical model was developed and experimentally validated for the steel 1.1274 in previous research. Nevertheless, minor deviations have occurred in the prediction of final curvatures of the different stable geometries and it is still unclear to what extent other influencing variables such as shell thickness or material properties influence the achievability of fully closed bistable shells. Therefore, in this paper, an enhancement and generalization of the existing semi-analytical model for different steels is described and the extended model is used for a comprehensive analysis of the influence of different variables on bistability and final shell geometries.

Denmark is a pioneer in the large-scale extraction of the sustainable energy of the wind, especially in theelectricity sector which supplies most of the Danish electricity consumption. A combination of these recentDanish successes, and the increased societal demand for the reduction of carbon dioxide emission in light ofthe recent IPCC report, has created the expectation of a fast transition from fossil fuel to sustainable energyresources in all energy sectors. Although this transition is inevitable due to the unsustainable nature of fossilfuels and the declining Danish oil and gas production, there is still an ongoing discussion, sometimessupported by qualitative evidence, on its possibility, extent, and urgency.This paper that is inspired by a true story of an unsuccessful date between a petroleum engineeringcolleague and a Danish environmentalist has a quantitative look at the future energy balance of Denmark byestimating the future energy consumption of a typical Dane and comparing it with the available renewableand non-renewable energy resources. It also suggests and compares different scenarios for a self-sufficientDenmark with 100% renewable energy, considering the available land and shallow sea and the footprint ofthe energy extraction and storage methods in Denmark. The results show that if the intermittency problem ofthe wind energy is addressed in the future, there is still a large demand, mostly from the transport sector, forliquid fuels with high energy-density, which needs to be addressed by a paradigm shift in transporttechnologies or large scale implementation of power to fuel technologies with a sustainable carbon source.

The article describes the characteristics of wood pulp fibers. The types of regenerated cellulose modifications, properties of microfibre materials, and areas of application of nanocellulose materials are considered.

Cemented paste backfill (CPB) comprising mineral tailings, binders and mixing waters is an important potential support material in the mining industry. As the mechanical properties of CPB are significantly influenced by its microstructural characteristics the development of measurement tools to better understand its pore structure evolution is important for its increased utilisation. This study reports the application of low-field nuclear magnetic resonance (NMR) relaxation time measurements to characterise the microstructural evolution of CPB materials over 56 days of hydration, contrasting common tap water and hypersaline water (~22 wt% salt) as mixing waters. Distinct NMR relaxation time populations were evidenced within each CBP sample, revealing the presence of both capillary (T1,2 ≈ 10 ms) and gel pore water (T1,2 ≈ 300 – 500 µs), with time-dependent relaxation measurements facilitating characterisation of capillary pore structure evolution over the hydration period assessed. Hypersaline samples demonstrated a time-lag in this measured capillary pore evolution, relative to those hydrated with tap water, while pore structure evolution rates were observed to increase with increased CPB binder content. Further, both T1 and T2 NMR relaxation times were found to correlate with the uniaxial compressive strength of the CPB materials investigated, facilitating the formulation of a predictive correlation function between NMR relaxation characteristics and mechanical properties.

This paper presents the development of a three-dimensional non-linear finite element model to predict the moment-rotational response of partial depth endplate composite connections. A parametric study is performed to evaluate the influence of utilizing various sizes (i.e., length, width, and thickness) of external Carbon Fiber Reinforced Polymer (CFRP) laminates on the composite connection performance. The numerical analysis reveals that the flexural resistance of the retrofitted CFRP strengthened composite connection increases by up to around 20% and the rotation capacity decreases by approximately 60%. Moreover, the results indicate that applying CFRP laminate to the tension face of the composite slab can reduce the amount of rebar needed for the bending capacity of steel-concrete composite beam-to-column connections.

The paper reports the mechanical properties of 4H-SiC die with different thicknesses, that have been determined through a 3-point bending (3-PB) test. In particular, it reports 1) the measurement of the failure strength of thin 4H-SiC rectangular die; 2) the Weibull analysis of the failure strength of 4H-SiC die, exploited to determine the maximal load that can be applied to the die, without any breakage; 3) the measure of 244±15 GPa for the flexural Young modulus E of SiC die, gained from the 3-PB test elaborations.

This article objectively assesses, the hypothesis of the streamline's shape theory and its formulated equation. The deduction of proof uses algebra rather than first-order partial differential equations to address the specific hypothesis of "Streamline's shape theory" from the fundamental perspective of applied mathematics and scientifically derives mathematical relations of the axioms and corollaries in the field of fluid dynamics. The algebraic methods employed provide progressively more distinct and precise solutions compared to first-order partial differential equations. The foremost objective of this work is to evaluate if the formulations of the streamline's shape theory can have solutions for inviscid-incompressible and viscid-compressible flows of Newtonian fluids and to identify their nature. Secondly, to understand how the topology of the body and the free-stream conditions affect these solutions with due regards to the shape and size of the body interacting with the fluid flow. Finally, to explore the possibility of this theory to develop a CFD solver for streamline simulation to reduce the experimentation in the analysis of flow-structure interactions of Newtonian fluids and also to identify its scope of applications and limitations.

The photosensitivity of high germanium content optical fiber was investigated with reference to UV laser of 266nm center wavelength. Bragg gratings were inscribed into the fiber using scanning phase mask method with a 266nm ultra short pulse laser and refractive index modulation due to irradiation was calculated from the parameters of the resulting fiber Bragg gratings. At small fluence, the high germanium content optical fibers seemingly experience competing photosensitivity mechanisms, dissimilar to the characteristics of common photosensitive optical fibers.

Transportation of high concentrated fibrous materials to the disk mill grinding zone may be accompanied by problems when the fibrous material clogs the knife gap and causes subsequent failure of the grinding equipment. The article considers one of the few recommendations helping to eliminate this negative effect taking into account main technological factors of the grinding process.

The article presents results of experimental studies of cellulose properties depending on different shaped knife tooling of the disk mill used for grinding. A method for production of powdered cellulose material with characteristics close to microcrystalline cellulose is considered.

The article presents a brief analysis of various processing methods for fibrous materials

The natural origin of the fibers combined with random production flaws results in significant uncertainties in the properties of natural fiber reinforced composites. A probabilistic assessment can help to characterize the uncertainties and evaluate the reliability of natural fiber composites, enabling their use in engineering designs. Toward this end, this study aims to quantify the uncertainties in the tensile strength and frequency response of a unidirectional flax/epoxy composite due to the variability of various input parameters, including the fiber material properties and manufacturing flaws. Based on the available data in the literature, the non-deterministic input variables were divided into normal and uniform variables using a statistical test. A computationally efficient response surface approach based on the polynomial chaos expansion was adopted to conduct the uncertainty analysis with multi-type uncertain variables. Moreover, the results were validated by the direct Monte Carlo simulation to demonstrate the accuracy and efficiency of the surrogate model.

Porous implants must satisfy several physical and biological requirements in order to be promising materials for orthopedic application: they should have the proper levels of stiffness, permeability, and fatigue resistance and in proximity to how much they are in bone tissues. In recent years, several experimental, numerical, and analytical studies have been carried out on the influence of unit cell geometry on such properties. Even though experimental and numerical techniques can effectively study and predict the behavior of different micro-structure, they lack the ease the analytical relationships provide for such predictions. Even though it is well-known that Timoshenko beam theory gives much better accuracy in predicting the deformation of a beam (and as a result lattice structures), many of the already-existing relationships in the literature have been derived based on Euler-Bernoulli beam theory. The question that arises here is that can there be a convenient way to convert the already-existing relationships based on Euler-Bernoulli to relationships based on Timoshenko beam theory without the need to rewrite all the derivations from the starting point. In this paper, this question is addressed and answered, and a simple approach is presented. This technique is applied to six unit cells for which Euler-Bernoulli analytical relationships could be found in the literature, but Timoshenko theories could not be found: BCC, hexagonal packing, rhombicuboctahedron, diamond, truncated cube, and truncated octahedron. The results of this study demonstrated that converting analytical relationships based on Euler-Bernoulli to equivalent Timoshenko ones can decrease the difference between the analytical and numerical values for one order of magnitude which is a significant improvement in accuracy of the analytical formulas. The methodology presented in this study is not only beneficial to the already-existing analytical relationships but also facilitates derivation of accurate analytical relationships for other, yet unexplored, unit cell types.

This paper presents the results of experimental studies of the process of grinding fiber semi-finished products, the specific power consumption for its implementation with different refining disks in the production of fiberboard.

In this paper, we discuss an improved concept for a cavity receiver unit for Solar Parabolic Trough Collectors (PTC) with the application of hot mirror coating (HMC) on a cavity aperture. This design aims to lessen radiant energy losses while operating at higher temperatures by incorporating a variety of optically active layers. We present the theoretical background, which we derived in previous work, and the resulting implementation in a simulation code. We next discuss the layout and results of an experiment, which allowed us to make contact with the simulation with minor adjustments It was seen that the correspondence between the experiment and simulation results was encouragingly close (Chi-squared p > 0.8 and p > 0.95), and we proceeded to investigate simulations of different receiver designs. Simulated outcomes for the temperature of the heat transfer fluid, temperature maps, and efficiencies are presented. Our proposal indicates temperature-related benefits when compared to other popular designs in terms of the heat transfer fluid temperature and efficiency.

The industrial use of laser powder-bed fusion (L-PBF) in turbomachinery is gaining momentum rendering the inspection and quali?cation of certain post-processing steps necessary. This includes fusion techniques that allow to print multiple parts separately to take advantage of e.g. various print orientations and join them subsequently. The main motivation of this study is to validate the tungsten inert gas (TIG) welding process of L-PBF manufactured parts using industrial speci?cations relevant for gas turbines to pave the way for the industrial production of modular build setups. For this, two commonly used nickel-based super alloys for high-temperature applications, Inconel 718 and Inconel 625 are chosen. Since their defect-free printability has been established widely, we focus on the suitability to be joined using TIG welding. The process is evaluated performing microstructural examination and mechanical tests in as-built as well as heat-treated samples. The welds are assessed by applying a general weld quali?cation approach used at Siemens Gas and Power. It was found that both materials can be joined via TIG welding using standard weld parameters causing minimal defects. A solution annealing heat treatment before welding is not necessary for a positive outcome, but still recommended for Inconel 718.

In reluctance and permanent magnet synchronous machines, flux barriers are crucial for magnetic flux guidance. Designed as cutouts, flux barriers reduce the mechanical strength of the rotor construction. To operate these electric drives at higher rotational speed, an alternative flux barrier design is required. Since residual stress influences the magnetic properties of soft magnetic materials, this paper deals with embossing induced residual stress as flux barriers in non-oriented electrical steel with 2.4 wt% silicon and a sheet thickness of 0.35 mm. The investigated flux barriers were fabricated with a cylindrical or spherical punch at two different penetration depths and were compared to a flux barrier fabricated as cutout. A residual stress analysis using Finite Element Analysis helps understanding the mechanism of embossed flux barriers. Additionally, the influence of induced residual stress on the magnetic material behavior is measured using standardized single sheet tests and neutron grating interferometry measurements. This investigation aimed at a better understanding of the flux barrier design by local induction of residual stress.

Carbon nanotube (CNT) is one of the most promising nanomaterials to increase the elastic modulus of cementitious composites. However, CNT characteristics, dispersion procedure, and matrix composition/hydration are critical and correlated with a high degree of uncertainty in achieving a desirable performance. This paper proposes a mechanics-based model to predict the elastic modulus of CNT reinforced cementitious materials based on the Halpin-Tsai equation. The current study employs a probabilistic approach to consider the influences of multiple experimental variables and various sources of uncertainty associated with them. To this end, first, a Bayesian methodology is adopted to perform the model validation, evaluation, and selection procedures using extensive literature test data. Then, the optimum ranges of variables are found to maximize the chance of achieving a certain target modulus (herein, 50% more than control) using a reliability analysis. The proposed model suggests that the highest elastic modulus is achieved when using CNT aspect ratio ranges from 400 to 800 and concentration between 0.08 and 0.18 c-wt%. Also, the experimentally observed elastic modulus and the proposed probabilistic model exhibit a similar trend. For example, the importance of hydration age increases as CNT concentration increases.Finally, the proposed model can be used to reliably predict the elastic modulus, guiding future researchers to design more efficiently.

The bond between carbon nanotubes (CNTs) and cementitious materials is the key characteristic for predicting the flexural strength. However, the dispersion quality dominantly changes bond mechanisms. A probabilistic approach can benefit a robust model development to capture various relations. This study proposes a probabilistic model based on the deterministic Kelly-Tyson theory to predict the flexural strength of CNT reinforced cementitious materials. The proposed model considers the influences of multiple experimental variables and their interactions on CNT dispersion quality and the flexural strength. A Bayesian methodology is adopted to calibrate the unknown model parameters and their statistical uncertainty using extensive experimental test results from the literature including the authors’ work. The proposed model can be reliably used to predict the flexural strength with reasonable accuracy.

The bond between carbon nanotubes (CNTs) and cementitious materials is the key characteristic for predicting the flexural strength. However, CNT dispersion quality may change the bonding mechanism. A probabilistic approach can benefit the deterministic models to capture the uncertainties affecting these characteristics. This study proposes a probabilistic model using the Kelly-Tyson theory to predict the flexural strength of CNT-cement nanocomposites. The proposed model considers the effects of experimental variables on CNT dispersion quality, bonding mechanism and the flexural strength. To this end, a Bayesian methodology is employed to calibrate the unknown model parameters and various sources of uncertainty using extensive test data. The model is then used to identify the optimum ranges of variables to maximize the flexural strength through computing the failure probability which is defined as the probability of not meeting certain strength requirements (herein, 50% increase compared with the control). The model suggests that CNT aspect ratio ranges from 400 to 800 and concentration between 0.08 and 0.18 c-wt% yields the highest flexural strength. Finally, the effect of changes in experimental variables on the probability estimates is examined using sensitivity and importance measures. The analysis reveals that the proposed model can capture the experimentally observed trends with reasonable accuracy. For example, the importance of age increases as CNT concentration increases.

Contemporary three-dimensional printing, also referred to as additive manufacturing, has been popular for rapid prototyping due to its capacity for relatively facile design iteration and low investment per prototype. Object fabrication speeds, however, have lagged behind other manufacturing technologies, and existing approaches for accelerating the printing process are limited in their applicability and accessibility. This work explores the viability of using sanded FEP films as resin-irradiation window interface layers in inverted vat polymerization additive manufacturing for reducing layer separation requirements and expediting the printing process. The effects of sanding FEP films on the equilibrium contact angle of commercial vat polymerization resin on the FEP films are investigated, and the forces required to separate cured resin from the FEP films in a simulated inverted vat polymerization setup are explored. Scanning electron microscopy is used to reveal the effects of wear on these sanded surfaces. The findings of this work offer insight into methods for dramatically accelerating existing additive manufacturing and vat polymerization systems.

The implementation of additive manufacturing techniques in the production of mission critical structural components is challenged by its low throughput and limited build envelope. In recent years, hybrid production methods are emerging to bridge between the build volume and high throughput of conventional production methods and the design freedom enabled by additive manufacturing. The repeatability of material properties and the quality of the interface between the additive manufactured and wrought material are crucial for the adoption of hybrid manufacturing techniques by the industry. Here, the tensile behavior and fracture toughness of a hybrid Ti6Al4V alloy are examined in detail. Ti6Al4V pre-forms were built onto a wrought Ti6Al4V start-plate and extracted via milling. Compact tension and uniaxial tension specimens, extracted from the hybrid pre-forms demonstrated good fracture and properties with no preference for crack growth in neither the AM or wrought materials. Microstructural characterization revealed a sharp interface between the two materials with no evidence of a heat-affected zone. The hybrid manufacturing approach studied here expands the current limitations of large scale critical components with fine features and allow such structures to be produced with a higher thruput.

With an increase in the use of carbon fiber composites in the aerospace and automobile industry a collateral issue of what to do with end-of-life carbon fiber composites has risen. In this study, we successfully developed a second-generation composite using a heterogenous mixture of thermoset and thermoplastic recycled carbon fiber composites (CFCs). The recovered vinyl ester and epoxy CFCs were characterized using thermogravimetric analysis. Adhesive performance was evaluated through double lap shear tests by melt-bonding a thermoplastic polyether ether ketone (PEEK) CFC to either the thermoset epoxy or vinyl ester CFC. The waste carbon fiber composites were also mechanically milled and classified through screening techniques. The resulting milled materials were used to form and produce composite panels through high temperature compression molding. The influence of particle size and platen temperature were evalauted through mechanical testing. Results indicate that melt-bonding with the vinyl ester/CFC exhibited significantly higher lap shear strength values than that between epoxy/CFC and PEEK. Findings also show that adding thermoset CFCs to the thermoplastic system (PEEK) enhanced the flexural properties of composites.

Shear cutting is used for manufacturing various parts ranging from e.g. simple washers to complex gears. The latter are typically subjected to cyclic loading and fail foremost due to fatigue damages. Hereby, the parts lifetime is mainly determined by: the geometry, the applied load, the material, the hardness, the roughness and the residual stress state. While numerous research works deal with the influence of the process parameters on the hardness and the parts geometry, the influence of the process parameters on the residual stress state and on the resulting fatigue strength has not been investigated in detail, yet. In an earlier publication, suitable shear cutting techniques, which allow to achieve a high amount of clean-cut and a favorable residual stress state were compared. In this paper, the influence of the process parameters on the residual stress state and the resulting bending fatigue strength are addressed. To simulate the bending stress occurring in the tooth root, C-shaped specimens were manufactured by different blanking techniques. The die-clearance and punch and die edge radii were varied with these blanking techniques. After measuring the cut-surface geometry, the hardness distribution and the surface roughness, the fatigue strength was determined in a pulsating test rig. By carrying out residual stress measurements using x-ray diffraction and simulating the material flow behavior using the Finite-Element-Method, basic mechanisms, which are influencing the residual stress state and the resulting bending fatigue strength, were identified and will be presented and discussed in the paper.

In this work we first solve the radiative heat transfer problem in one dimension to perform a comparative analysis of the time-averaged performance of the partially transparent radiative windows and radiative coolers. In doing so, we clearly distinguish the design goals for the partially transparent windows and radiative coolers and provide optimal choice for the material parameters to realize these goals. Thus, radiative coolers are normally non-transparent in the visible, and the main goal is to design a cooler with the temperature of its dark side as low as possible relative to that of the atmosphere. For the radiative windows, however, their surfaces are necessarily partially transparent in the visible. In the cooling mode, the main question is rather about the maximal visible light transmission through the window at which the temperature on the window somber side does not exceed that of the atmosphere. We then demonstrate that transmission of the visible light through smart windows can be significantly increased (by as much as a factor of 2) without additional heating of the windows. This is accomplished via coupling the windows to the radiative coolers using transparent cooling liquid that flows inside of the window and radiative cooler structures. We also demonstrate that efficient heat exchange between radiative coolers and smart windows can be realized using small coolant velocities (sub-1 mm/s for ∼ 1 m large windows) or even using a purely passive gravitationally driven coolant flows between a hot smart window and a cold radiative cooler mounted on top of the window with only a minimal temperature differential (sub-1K) between the two. We believe that our simple models complemented with an in-depth comparative analysis of the standalone and coupled smart windows and radiative coolers can be of interest to a broad scientific community pursuing research in these disciplines.

A mathematical model is presented which is designed to be applicable to Coronavirus case data from any country and which can serve as a tool to carry out predictive analysis and sensitivity analysis with the goal of minimizing virus related deaths. The model has been successfully applied to Covid-19 case data in five countries – China, South Korea, Iran, Italy and the USA. The model is versatile and can be applied to other countries and regions as well.

Additively-manufactured (AM) materials have a defined mesostructure and natural voids which impact their structural stability; thin shells which so not have bulk to support or absorb the effects of the variances in properties are particularly affected. Thin shells are a common feature in many designs, providing good strength-to-weight ratios for many applications, particularly in the aerospace and structural design domains. The use of AM processes to produce thin structures could both expand the use of AM and improve the application space for thin structures in design, but this problem has not yet been widely explored for buckling cases. The brief exploratory study presented in this paper examined the characteristics and critical buckling load of thin-walled ABS and PLA cylinders under static axial and angled radial loading. A designed 2(4-1) factorial experiment was used to explore the buckling behavior, examining the impact of wall thickness, material, and two kinds of internal reinforcement (soft infill and polyurethane foam). Analysis of variance (ANOVA) (including model adequacy testing and proof of Fisher Assumption validity) was completed on data from two replications (32 total tests), providing useful information on the significance of the factors and their interactions. The data is provided in full, along with a discussion of the experimental design and testing method, the results, and the importance of this problem in further research efforts. The results of the tests showed a dramatic variance in the performance based on the characteristics of the cylinders. The data collected can be used to drive future work toward the modeling and design of hard polymer AM thin structures, as well as developing efficient and low-cost methods for testing and exploring these structures for practical design problems.