A hyperelastic material model considering biaxial coupling of tension–compression and shear for the forming simulation of woven fabrics

In the past decades, numerous material models have been developed to describe the forming behavior of fabrics, allowing for modeling of complex forming processes. Especially under constrained forming conditions, distinct multiaxial stress states can occur, which need to be captured by macroscopic material models. In this paper, a nonlinear hyperelastic constitutive model is presented and implemented in an Abaqus/Explicit user subroutine Vumat, considering biaxial coupling and normal-shear coupling of the interwoven fiber bundles in a woven fabric. The couplings are formulated for positive and negative normal strains. Exemplary forming studies on the generic double dome geometry are performed to investigate the influence of the couplings on the forming result. The results show that the biaxial coupling should be considered under highly constrained boundary conditions in thickness direction. The normal-shear coupling affects the forming behavior only under very high draping angles and appears to be of less relevance in these conditions

The Direct Sandwich Composite Molding (D-SCM) Process: Sandwich Manufacturing and Characterization

Sandwich structures benefit from the geometrical stiffening effect due to their high cross-sectional area moment of inertia. Transferred to carbon fiber-reinforced plastic (CFRP) components, the needed amount of carbon fiber (CF) material can be reduced and with it the CO$_{2}$ footprint. The combination of a light foam core with continuous fiber-reinforced face sheets is a suitable material combination for lightweight design. Traditionally, CFRP sandwich structures with a foam core are manufactured in a two-step process by combining a prefabricated foam core with fiber-reinforced face sheets. However, in addition to the reduction in the used CFRP material, manufacturing processes with a high efficiency are needed. The objective of this paper is the sandwich manufacturing and characterization by using the Direct Sandwich Composite Molding (D-SCM) process for the one-step production of CFRP sandwich structures. The D-SCM process utilizes the resulting foaming pressure during the reactive polyurethane (PUR) foam system expansion for the impregnation of the CF-reinforced face sheets. The results of this work show that the production of sandwich structures with the novel D-SCM process strategy is feasible in one single manufacturing step and achieves good impregnation qualities. The foam density and morphology significantly influence the core shear properties and thus the component behavior under a bending load

Material modelling of fabric deformation in forming simulation of fiber-metal laminates - A review on modelling fabric coupling mechanisms

During forming of complex fiber-metal laminates (FML), compressive stress zones occur. In pure textile forming, these compressive stresses typically lead to extensive wrinkling. In FML forming, however, wrinkling is partly hindered by the metal layers. Thus, combined stress states occur, where compression influences the deformation. In forming simulation, these compressive stresses can lead to erroneous formation of shear bands within the fabric layer, if the deformation behavior is not modelled correctly. Simple fabric models neither consider interactions between roving directions nor model interactions between membrane strains and shear strains. More advanced invariant-based hyperelastic material models are able to capture these interactions, but only consider tension and shear, while disregarding compression. A common assumption is to set the fabric compression stiffness close to zero. Experimentally, the in-plane fabric compression stiffness has not been determined so far. However, in FML forming, the compression stiffness and the combined compressiontension- shear behavior becomes relevant. In this article, the authors summarize and analyze the capacity of state-of-the-art fabric material models to predict the deformation behavior of fabrics under combined loading. Based on these findings, conclusions are drawn for a new macroscopic modeling approach for woven fabrics, including coupling of tension, compression and shear

Towards 3D Process Simulation for In-Situ Hybridization of Fiber-Metal-Laminates (FML)

Fiber-metal-laminates (FML) provide excellent fatigue behavior, damage tolerant properties, and inherent corrosion resistance.To speed up manufacturing and simultaneously increase the geometrical complexity of the produced FML parts, Mennecart et al. proposed a new single-step process combining deep-drawing with infiltration (HY-LCM). Although the first experimental results are promising, the process involves several challenges, mainly originating from the Fluid-Structure-Interaction (FSI) between deep-drawing and infiltration. This work aims to investigate those challenges to comprehend the underlying mechanisms. A new close-to-process test setup is proposed on the experimental side, combining deep-drawing of a hybrid stack with a linear infiltration. A process simulation model for FMLs is presented on the numerical side, enabling a prediction of the dry molding forces, local Fiber Volume Content (FVC) within the three glass fiber (GF) interlayers, and simultaneous fluid progression. The numerical results show that the local deformation of the hybrid stack and required forces are predictable. Furthermore, lateral sealing of the hybrid stacks leads to deviations from the intended initially one-dimensional fluid progression. Eventually, the numerical results demonstrate that most flow resistance originates from geometrically critical locations. Future experimental and numerical work will combine these insights to focus on the flow evaluation during deformation and a successful part-level application

Circadian Clocks in Mouse and Human CD4+ T Cells

Though it has been shown that immunological functions of CD4+ T cells are time of day-dependent, the underlying molecular mechanisms remain largely obscure. To address the question whether T cells themselves harbor a functional clock driving circadian rhythms of immune function, we analyzed clock gene expression by qPCR in unstimulated CD4+ T cells and immune responses of PMA/ionomycin stimulated CD4+ T cells by FACS analysis purified from blood of healthy subjects at different time points throughout the day. Molecular clock as well as immune function was further analyzed in unstimulated T cells which were cultured in serum-free medium with circadian clock reporter systems. We found robust rhythms of clock gene expression as well as, after stimulation, IL-2, IL-4, IFN-γ production and CD40L expression in freshly isolated CD4+ T cells. Further analysis of IFN-γ and CD40L in cultivated T cells revealed that these parameters remain rhythmic in vitro. Moreover, circadian luciferase reporter activity in CD4+ T cells and in thymic sections from PER2::LUCIFERASE reporter mice suggest that endogenous T cell clock rhythms are self-sustained under constant culture conditions. Microarray analysis of stimulated CD4+ T cell cultures revealed regulation of the NF-κB pathway as a candidate mechanism mediating circadian immune responses. Collectively, these data demonstrate for the first time that CD4+ T cell responses are regulated by an intrinsic cellular circadian oscillator capable of driving rhythmic CD4+ T cell immune responses

TRY plant trait database – enhanced coverage and open access

Plant traits - the morphological, anatomical, physiological, biochemical and phenological characteristics of plants - determine how plants respond to environmental factors, affect other trophic levels, and influence ecosystem properties and their benefits and detriments to people. Plant trait data thus represent the basis for a vast area of research spanning from evolutionary biology, community and functional ecology, to biodiversity conservation, ecosystem and landscape management, restoration, biogeography and earth system modelling. Since its foundation in 2007, the TRY database of plant traits has grown continuously. It now provides unprecedented data coverage under an open access data policy and is the main plant trait database used by the research community worldwide. Increasingly, the TRY database also supports new frontiers of trait‐based plant research, including the identification of data gaps and the subsequent mobilization or measurement of new data. To support this development, in this article we evaluate the extent of the trait data compiled in TRY and analyse emerging patterns of data coverage and representativeness. Best species coverage is achieved for categorical traits - almost complete coverage for ‘plant growth form’. However, most traits relevant for ecology and vegetation modelling are characterized by continuous intraspecific variation and trait–environmental relationships. These traits have to be measured on individual plants in their respective environment. Despite unprecedented data coverage, we observe a humbling lack of completeness and representativeness of these continuous traits in many aspects. We, therefore, conclude that reducing data gaps and biases in the TRY database remains a key challenge and requires a coordinated approach to data mobilization and trait measurements. This can only be achieved in collaboration with other initiatives

The genetic architecture of the human cerebral cortex

The cerebral cortex underlies our complex cognitive capabilities, yet little is known about the specific genetic loci that influence human cortical structure. To identify genetic variants that affect cortical structure, we conducted a genome-wide association meta-analysis of brain magnetic resonance imaging data from 51,665 individuals. We analyzed the surface area and average thickness of the whole cortex and 34 regions with known functional specializations. We identified 199 significant loci and found significant enrichment for loci influencing total surface area within regulatory elements that are active during prenatal cortical development, supporting the radial unit hypothesis. Loci that affect regional surface area cluster near genes in Wnt signaling pathways, which influence progenitor expansion and areal identity. Variation in cortical structure is genetically correlated with cognitive function, Parkinson's disease, insomnia, depression, neuroticism, and attention deficit hyperactivity disorder

Large expert-curated database for benchmarking document similarity detection in biomedical literature search

Document recommendation systems for locating relevant literature have mostly relied on methods developed a decade ago. This is largely due to the lack of a large offline gold-standard benchmark of relevant documents that cover a variety of research fields such that newly developed literature search techniques can be compared, improved and translated into practice. To overcome this bottleneck, we have established the RElevant LIterature SearcH consortium consisting of more than 1500 scientists from 84 countries, who have collectively annotated the relevance of over 180 000 PubMed-listed articles with regard to their respective seed (input) article/s. The majority of annotations were contributed by highly experienced, original authors of the seed articles. The collected data cover 76% of all unique PubMed Medical Subject Headings descriptors. No systematic biases were observed across different experience levels, research fields or time spent on annotations. More importantly, annotations of the same document pairs contributed by different scientists were highly concordant. We further show that the three representative baseline methods used to generate recommended articles for evaluation (Okapi Best Matching 25, Term Frequency-Inverse Document Frequency and PubMed Related Articles) had similar overall performances. Additionally, we found that these methods each tend to produce distinct collections of recommended articles, suggesting that a hybrid method may be required to completely capture all relevant articles. The established database server located at https://relishdb.ict.griffith.edu.au is freely available for the downloading of annotation data and the blind testing of new methods. We expect that this benchmark will be useful for stimulating the development of new powerful techniques for title and title/abstract-based search engines for relevant articles in biomedical research.Peer reviewe