Folding responses of origami-inspired structures connected by groove compliant joints

Folding responses of a set of notch-type compliant joint candidates are first numerically explored before the victorious one is implemented in actuating the deployment of Miura origami-inspired plate structure. The considered notch-type compliant joints are groove, elliptical holes, rectangular holes, and outside LET types. The exploration and examination of the kinematic and dynamic characteristics of these joints include performance indicators such as stress contour, load-deformation, moment-angle, and stiffness-angle relationships for different geometric parameters, with a specific interest in their hysteretic behaviors. Considering various performance features, the groove joints have been identified as the most suitable to be employed as the Miura origami-inspired hinge. The Miura origami-inspired plate folding behaviors are further explored considering various numbers and placements of groove joints. It has been found that the Miura plate performs better with the groove joint compared to that without one and that the single and double groove joint modes are inter-correlated. The study offers a comprehensive understanding of the effects of geometrical variation of numerous compliant joints on the folding behaviors as well as the further implementation of the victorious one in actuating the deployment of the Miura origami-inspired plate structure in accordance with the number and location of the joint.

Fabrication robustness in BIC metasurfaces

All-dielectric metasurfaces supporting photonic bound states in the continuum (BICs) are an exciting toolkit for achieving resonances with ultranarrow linewidths. However, the transition from theory to experimental realization can significantly reduce the optical performance of BIC-based nanophotonic systems, severely limiting their application potential. Here, we introduce a combined numerical/experimental methodology for predicting how unavoidable tolerances in nanofabrication such as random geometrical variations affect the performance of different BIC metasurface designs. We compare several established all-dielectric BIC unit cell geometries with broken in-plane inversion symmetry including tilted ellipses, asymmetric double rods, and split rings. Significantly, even for low fabrication-induced geometrical changes, both the BIC resonance amplitude and its quality factor (Q-factor) are significantly reduced. We find that the all-dielectric ellipses maintain the highest Q-factors throughout the geometrical variation range, whereas the rod and split ring geometries fall off more quickly. The same behavior is confirmed experimentally, where geometrical variation values are derived from automated processing of sets of scanning electron microscopy (SEM) images. Our methodology provides crucial insights into the performance degradation of BIC metasurfaces when moving from simulations to fabricated samples and will enable the development of robust, high-Q, and easy to manufacture nanophotonic platforms for applications ranging from biomolecular sensing to higher harmonic generation.

Salt morphologies and crustal segmentation relationship: new insights from Western Mediterranean Sea and other salt passive margins

<p>Salt tectonics at salt-bearing margins is often interpreted as the combination of gravity spreading and gravity gliding, mainly driven by differential sedimentary loading and margin tilting, respectively. Nevertheless, in the Western Mediterranean Sea, the classical salt tectonics models are incoherent with its morpho-structural setting: the Messinian salt was deposited in a closed system, formed several Ma before the deposition, horizontally in the entire deep basins, above a homogenous multi-kilometre pre-Messinian thickness. The subsidence is purely vertical in the deep basin, implying a regional constant initial salt thickness, the post-salt overburden is homogenous and the distal salt deformation occurred before the mid-lower slope normal faults activation. Instead, the compilation of MCS and wide-angle seismic data highlighted a clear coincidence between crustal segmentation and salt morphology domains. The geometrical variation of salt structures seems to be related to the underlying crustal nature segmentation. Regional thermal anomalies and/or fluid escapes, associated with the exhumation phase, or the mantle heat segmentation, could therefore play a role in adding a further component on the already known salt tectonics mechanisms. The compilation of crustal segmentation and salt morphologies in different salt-bearing margins, such as the Santos, Angolan, Gulf of Mexico and Morocco-Nova Scotia margins, seems to depict the same coincidence. In view of what is observed in Western Mediterranean Sea, the heat segmentation influence in the passive margins should not be overlooked and deserves further investigation.</p>

EFFICIENT SPOT WELDING SEQUENCE SIMULATION IN COMPLIANT VARIATION SIMULATION

Geometrical variation is one of the sources of quality issues in a product. Spot welding is an operation that impacts the final geometrical variation of a sheet metal assembly considerably. Evaluating the outcome of the assembly, considering the existing geometrical variation between the components, can be achieved using the Method of Influence Coefficients (MIC), based on the Finite Element Method (FEM). The sequence with which the spot welding operation is performed influences the final geometrical deformations of the assembly. Finding the optimal sequence that results in the minimum geometrical deformation is a combinatorial problem that is experimentally and computationally expensive. Traditionally, spot welding sequence optimization strategies have been to simulate the geometrical variation of the spot-welded assembly after the assembly has been positioned in an inspection fixture. In this approach, the calculation of deformation after springback is one of the most time-consuming steps. In this paper, a method is proposed where the springback calculation in the inspection fixture is bypassed during the sequence evaluation. The results show a significant correlation between the proposed method of weld relative displacements evaluation in the assembly fixture and the assembly deformation in the inspection fixture. Evaluating the relative weld displacement makes each assembly simulation less time-consuming, and thereby, sequence optimization time can be reduced by up to 30%, compared to the traditional approach.

Identification of Variation Sources for High Precision Fabrication in a Digital Twin Context

The aerospace industry is increasing its focus on fabrication in manufacturing, foregoing large castings to instead assemble and join smaller parts into final products. This increases the total amount of geometrical variation introduced during the production process, since the unique variation from each individual part can add to a propagating effect putting the final assembled product outside of tolerance limits. Geometry assurance and variation simulation has traditionally been applied as a part of the design process to develop robust manufacturing concepts that are as insensitive as possible to variation. A concept for geometry assurance has been proposed where variation simulation is conducted for each individual assembly using real measurements from incoming parts, making it possible to make adaptive adjustments to production parameters to optimize results. It is however not feasible to measure and simulate every aspect of the process. This paper provides a summary of relevant sources of geometrical variation for a high precision fabrication process, based on input from a fabrication process in the aerospace industry. Variation sources are analyzed and discussed from an industrial perspective, putting them in the context of an actual fabrication process as well as in the context of digital twins for geometry assurance.

On the recirculating flow of three-dimensional asymmetric bluff bodies

The paper investigates the role of geometrical asymmetric modifications of a rectangular flat-backed body on the properties of the recirculating flow at a Reynolds number $$Re=1.8\times 10^5$$ R e = 1.8 × 10 5 . The reference model has two reflectional symmetries denoted $$s_y$$ s y and $$s_z$$ s z in both spanwise directions. The flow is subjected to the static instability that leads to two mirrored wake states breaking the symmetry $$s_y$$ s y . Two families of geometrical variation of the fore-body and after-body are studied, each breaking one of the reflectional symmetries of the reference model. Geometrical modifications that preserve $$s_y$$ s y evidence possibilities of bistable dynamics suppression although the static instability persists. Geometrical modifications that do not preserve $$s_y$$ s y produces a large unbalance of both wake states in accordance to recent observations on real cars (Bonnavion et al. in J Wind Eng Ind Aerodyn 184:77–89, 2019). Results offer perspectives for potential drag reduction induced by appropriate coupling of bluff body geometry and wake state selection. Graphic abstract

Effect of selective laser heat treatment on geometrical variation in boron steel components: An experimental investigation

Selective laser heat treatment is a well-known process for its ability to produce tailor heat treated blanks (THTB). Specifically, ultra high strength boron steels with tailored material properties can be produced. However, this process generates unwanted distortion and influences geometrical variation. This in turn can affect functionality, aesthetics, and performance of the final product. Understanding the effects on geometrical variation in the final product or the assembly will enable in designing and producing geometry assured products. In this paper, boron steel blanks were selectively laser heat treated with a specific heat treatment pattern and laser heating direction sequence. These heat treated blanks were then cold formed. Further on, spot welding simulation of the cold formed parts was performed to assess the effect on geometrical variation at the assembly level. The results show that the effect of selective laser heat treatment on geometrical variation at part level propagates further to the assembly level. It implies that the effect on geometrical variation should be minimized at part level, when the blanks are laser heat treated. Hence, the sources that influence geometrical variation at part level when employing selective laser heat treatment are presented and discussed. The motivation and possibilities to minimize the effects in the early design concept stages is provided.

Effects of geometric variations on buckling properties of carbon nanostructures: A finite element analysis

Critical Bucking Load (CBL) is one of the essential parameters to describe the mechanic stabilities of materials, e.g. the low-dimensional carbon nanostructures. While the CBL of pristine carbon nanotubes have been previously investigated using the quantum mechanics-based calculations, the effect of geometrical variation on the CBL of carbon nanomaterials is rarely reported since it need considerably large atomic models, which needs high computational cost. In this study, both the analytical and Finite Element (FE) methods were employed to systematically explore the impact of atomic vacancies, shapes and heterostructures on the CBLs of carbon nanomaterials with the acceptable computational cost. Our studies on the pristine CNTs first demonstrate the validity of the method we used. After that, the systems with mono-/bi-/tri-/pinole-vacancies either on nanocones, nanotube, linearly-joined nanotubes or angle-adjoined were simulated and analyzed. Our results reveal that the CBL values decrease with the increase of the aspect ratio of all considered nanomaterials. Based on the obtained results, the CBL of nanocone with the aspect ratio of 1, reduces significantly, from 50 nN to 10 nN when the aspect ratio is 3. The CBL of homogeneous, capped, and joint CNTs reduces to below 2 nN when the aspect ratio is above 14. The introduction of geometric variations can greatly affect the CBL values. The larger atomic vacancy has more serious impact on the CBLs. The most highlighted impact is for the pinhole vacancy where the CBL reduces to up to 70% of the original value. Our studies on linearly-joint and angle-joint carbon hybrids further demonstrate that the CBL can also be affected by the boundary conditions and joint structures of the hybrids.