Key Geometric Features Research Articles

Evaluation of Key Geometrical and Mechanical Properties for Remote Laser Welded AC-170PX Aluminium Joints

Use of lightweight materials to produce automotive body structures is one of the key trends adopted by automotive manufacturers to minimise emission of greenhouse gases, and subsequently, reduction of fuel consumption. Aluminium alloys are one of the promising lightweight materials which are increasingly used for automotive body-in-white structures. Such applications demand both efficient and effective joining/welding methods to produce repeatable, durable and strong joints without significant alteration of material properties. Remote laser welding (RLW) is an emerging joining technology and increasingly being used to produce lightweight joints as it satisfies the demand for high production throughput at low cost. This paper investigates the effects of process parameters when seam tracking remote laser welding is used to create an autogenous fillet edge weld of automotive grade aluminum alloy (AC-170PX) in lap configuration without shielding gas. The effects of laser power and welding speed on the key geometric features are reported together with details of the weld microstructure. Joint strength is evaluated by performing a lap shear test. It is found that the laser power and welding speed have dominant influence on key geometric features and subsequently on the lap shear strength. Relatively larger grain size in the fusion zone reduces the microhardness by up to 20% in comparison with the base material.

Comment on “Hubble flow variations as a test for inhomogeneous cosmology”

Saulder et al. (2019, A&A, 622, A83) have performed a novel observational test of the local expansion of the Universe for the standard cosmology as compared to an alternative model with differential cosmic expansion. Their analysis employs mock galaxy samples from the Millennium Simulation, a Newtonian N–body simulation on a ΛCDM background. For the differential expansion case the simulation has been deformed in an attempt to incorporate features of a particular inhomogeneous cosmology: the timescape model. It is shown that key geometrical features of the timescape cosmology have been omitted in this rescaling. Consequently, the differential expansion model tested by Saulder et al. (2019) cannot be considered to approximate the timescape cosmology.

Numerical modelling of the sound absorption spectra for bottleneck dominated porous metallic structures

Numerical simulations are used to test the ability of several common equivalent fluid models to predict the sound absorption behaviour in porous metals with “bottleneck” type structures. Of these models, Wilson’s relaxation model was found to be an excellent and overall best fit for multiple sources of experimental acoustic absorption data. Simulations, incorporating Wilson’s model, were used to highlight the relative importance of key geometrical features of bottleneck structures on the normal incidence sound absorption spectrum. Simulations revealed significant improvements in absorption behaviour would be achieved, over a “benchmark” structure from the literature, by maximising the porosity (0.8) and targeting a permeability in the range of 4.0 × 10−10 m2. Such a modelling approach should provide a valuable tool in the optimisation of sound absorption performance and structural integrity, to meet application-specific requirements, for a genre of porous materials that offer a unique combination of acoustic absorption and load bearing capability.

The mechanical response of cellular materials with spinodal topologies

The mechanical response of cellular materials with spinodal topologies is numerically and experimentally investigated. Spinodal microstructures are generated by the numerical solution of the Cahn-Hilliard equation. Two different topologies are investigated: ‘solid models,’ where one of the two phases is modeled as a solid material and the remaining volume is void space; and ‘shell models,’ where the interface between the two phases is assumed to be a solid shell, with the rest of the volume modeled as void space. In both cases, a wide range of relative densities and spinodal characteristic feature sizes are investigated. The topology and morphology of all the numerically generated models are carefully characterized to extract key geometrical features and ensure that the distribution of curvatures and the aging law are consistent with the physics of spinodal decomposition. Finite element meshes are generated for each model, and the uniaxial compressive stiffness and strength are extracted. We show that while solid spinodal models in the density range of 30–70% are relatively inefficient (i.e., their strength and stiffness exhibit a high-power scaling with relative density), shell spinodal models in the density range of 0.01–1% are exceptionally stiff and strong. Spinodal shell materials are also shown to be remarkably imperfection insensitive. These findings are verified experimentally by in-situ uniaxial compression of polymeric samples printed at the microscale by Direct Laser Writing (DLW). At low relative densities, the strength and stiffness of shell spinodal models outperform those of most lattice materials and approach theoretical bounds for isotropic cellular materials. Most importantly, these materials can be produced by self-assembly techniques over a range of length scales, providing unique scalability.

3D-Printed shoe last for bespoke shoe manufacturing

This paper presents a new approach for the production of bespoke shoe lasts used in shoe industry. It is based on measuring key geometric features of existing shoe lasts and establishing a parametric system which can then be used to create a 3D model of a customized fit shoe last. Thus, instead of 3D-scanning the foot and then doing time consuming and skill intensive point cloud data processing, the proposed solution requires only taking several measurements of the customer’s foot and inputting them into the parametric model to obtain the tailored shoe last 3D geometry. Furthermore, the internal geometry of this shoe last is topologically optimized to reduce material volume and 3D printing time, while still withstanding temperatures and loads specific to the shoe manufacturing process. The 3D model also includes geometrical features allowing the attaching of process-specific mounting hardware. Material Extrusion 3D Printing (ME3DP) was used to fabricate the shoe last from thermoplastic material. 3D-printed shoe lasts were tested in a real manufacturing setting, successfully producing bespoke canvas shoes with rubber soles. During testing, the shoe lasts were subjected to typical process loads and to high temperatures.

Hexagrid-Voronoi transition in structural patterns for tall buildings

In this paper, a first insight into the role that non-conventional structural patterns might play in the design of tall buildings is presented. The idea is to explore the mechanical properties of selected non-conventional structural patterns, in the form of both regular (Hexagrid) and irregular (Voronoi tessellation inspired) arrays, in order to assess their actual applicability in tall building design. For this aim, the concept of Representative Volume Element (RVE) and a classical homogenization-based micromechanical approach are employed for identifying the pattern units and deriving the relevant generalized stress-strain relationships. In the case of irregular patterns based on Voronoi diagrams, obtained by perturbing prescribed key geometrical features of hexagrids, a statistically significant sample of RVEs is defined on the basis of sensitivity analyses, and the related mechanical characterization is developed in statistical terms. Finally, a preliminary stiffness-based design procedure is proposed and applied to a tall building model with Voronoi exoskeleton. In conclusion, a discussion on the effectiveness of the design procedure and on the structural efficiency of the Voronoi patterns for tall buildings is presented

Microstructure and mechanical properties of gap-bridged remote laser welded (RLW) automotive grade AA 5182 joints

This study reports an investigation on the effects of process parameters and part-to-part gaps on joint quality when producing fillet edge joint using the novel gap-bridged remote laser welding (RLW) technique. Joint geometries, microstructural characteristics, scanning electron micrographs (SEM), electron backscatter diffraction (EBSD) maps, microhardness and tensile strength behaviours are reported for the autogenous RLW fillet edge welds in an aluminium alloy, AA5182, used extensively for automotive structural applications. It has been found that laser process parameters and part-to-part gap directly influence key geometric features including penetration, leg length and throat thickness of the weld fusion zone, and subsequently, tensile performance. Lap shear test results demonstrate that both laser power and speed greatly influence the maximum mean load at failure and the corresponding tensile extension. Furthermore, both the weld macrostructure sections and lap shear strength confirm that the gap-bridging RLW technique can be successfully applied to close the part-to-part gaps. The microhardness profiles reveal that under zero gap and gap-bridged conditions the AA 5182 alloy base material has lower hardness (5–10%) compared to fusion zone. The EBSD maps exhibit the grain distribution from the base material to fusion zone under different gap conditions. As a result of directional cooling, a plane of weakness was formed at the junction of the horizontal and vertical grain developments when part-to-part gaps were employed. This study shows that the gap-bridging RLW technique is capable of creating good quality performance joints with automotive grade AA5182 aluminium alloy.

Numerical studies of the influence of various geometrical features of a multispiked connecting scaffold prototype on mechanical stresses in peri-implant bone

The multispiked connecting scaffold (MSC-scaffold) prototype is an essential innovation in the fixation of components of resurfacing arthroplasty (RA) endoprostheses, providing their entirely non-cemented and bone-tissue-preserving fixation in peri-articular bone. An FE study is proposed to evaluate the influence of geometrical features of the MSC-scaffold on the transfer of mechanical load in peri-implant bone. For this study, an FE model of Ti-Alloy MSC-scaffold prototype embedded in a bilinear elastic, transversely isotropic bone material was built. For the compressive load on the MSC-scaffold, maps of Huber-Mises-Hencky (HMH) stress in peri-implant bone were determined. The influence of the distance between the bases of neighbouring spikes, the apex angle of spikes, and the height of the spherical cup of spikes of the MSC-scaffold were analysed. It was found that the changes in the distance between the bases of neighbouring spikes from 0.2 to 0.5 mm cause the HMH stress to increase in bone material by 32%. The changes of the apex angle of spikes from 2° to 4° decrease the HMH stress in bone material by 39%. The changes of height of the spherical cup of spikes from 0 to 0.12 mm increase the HMH stress in bone material by 24%. In conclusion, the spikes’ apex angle and the distance between the bases of spikes of the MSC-scaffold are the key geometrical features determining the appropriate MSC-scaffold prototype design. The built FE model was found to be useful in bioengineering design of the novel fixation system for RA endoprostheses by means of the MSC-scaffold.

A Novel Geometric Tolerance Modeling Inspired by Parametric Space Envelope

Tolerance is an essential part of design and manufacturing. It plays a key role in product quality and manufacturing costs. Understanding and controlling production variations on key geometric features can provide firms with a competitive edge. A model to link production variation to tolerance is highly desirable but difficult to build, especially for deformable parts with complex surfaces. Inspired by an innovative idea of volumetric space envelope (constructed from a base parametric curve), this paper proposes a novel spatial tolerance model. In this proposal, a volumetric envelope is superimposed onto the target manufacturing part, whose deformation and deviation (during manufacturing or assembly) are viewed as spatial variation, and this variation is modeled and linked to movements of envelope’s control points. This unique model design bypasses direct modeling of complex intrapart interactions, which is nonlinear in general and a major source of inaccuracy and low efficiency of many existing methods. The adopted indirect modeling brings many benefits. It can handle complex shapes and surfaces, and is able to take into account form errors. Also, it is capable of modeling both global and local variations observed in many practical cases. The new method is illustrated and verified through an example on a deformable vehicle door hinge plate. The proposed model shows application potential in every major stage of production, and makes possible to build a coherent cross-production life-cycle tolerancing framework from the early stage design, to manufacturing, to postproduction quality inspection. Note to Practitioners —Tolerance is a matter of everyday life to manufacturing and assembly engineers and designers. It directly impacts the product quality and production costs. Driven by the client’s ever-increasing variety needs, more and more deformable parts with complex surfaces have been entering into production in the past decade. However, existing degree of freedom (DOF) concept-based models, surrounding the idea of six DOFs of a rigid body, have difficulty in handling. While the decomposed type of models may help provide useful insight into the geometric variation, they are dependent on reliable measurement data, which may not be readily available. Motivated by the idea of deforming a manufacturing part indirectly through reshaping its surrounding (purposely designed) parametric space envelope (PSE), this paper proposes a novel spatial model for tolerancing. The proposed model is intuitive and is able to provide insight into geometric variations by visualizing them. Due to its novel model design, the proposed method can handle some fairly complex parts and surfaces (be it parametric or implicit) and is able to take into account form errors. The base curve to construct the PSE can be a Bezier curve, which is commonly available in computer-aided design/computer-aided manufacturing systems and is familiar to many practitioners (designers and engineers). This could substantially lower the application hurdle and open up a potentially wide application for the proposed method.

A Digital Analysis of the ″Digitally-Derived Geometric Design″ of the Front Wall of St. Paul′s Church in Macao -A Study on the Architecture and City of Macao, No. 1-

With reference to related historical archives and literature, this study conducted research into the history, the designer and the design dimensions of St. Paul′s Church in Macao. The remaining drawing of the facade merely reflects the correlation deduction of each controlling point in its geometric drawing. Through digital analysis, this study has further obtained the ″digitally-derived geometric design″ relations of the five-layer elevation design drawing and number-rounding adjustment of the constructing dimensions: the application of the law of equal-partition in the horizontal direction, the application of the law of upward successive-subtraction in stratification in the vertical direction, and the complicated combination of golden-rectangle controlling designs. The latter two applications are key geometrical features of Baroque Architecture.

The role of exposure time in computerized training of prostate cryosurgery: performance comparison of surgical residents with engineering students.

This study aims at the evaluation of a prototype of a computerized trainer for cryosurgery-the controlled destruction of cancer tumors by freezing. The hypothesis in this study is that computer-based cryosurgery training for an optimal cryoprobe layout is essentially a matter of exposure time, rather than trainee background or the specific computer-generated planning target. Key geometric features under considerations are associated with spatial limitations on cryoprobes placement and the match between the resulted thermal field and the unique anatomy of the prostate. All experiments in this study were performed on the cryosurgery trainer-a prototype platform for computerized cryosurgery training, which has been presented previously. Among its key features, the cryosurgery trainer displays the prostate shape and its contours and provides a distance measurement tool on demand, in order to address spatial constraints during ultrasound imaging guidance. Another unique feature of the cryosurgery trainer is an output movie, displaying the simulated thermal field at the end of the cryoprocedure. The current study was performed on graduate engineering students having no formal background in medicine, and the results were benchmarked against data obtained on surgical residents having no experience with cryosurgery. Despite fundamental differences in background and experience, neither group displayed superior performance when it comes to cryoprobe layout planning. This study demonstrates that computer-based training of an optimal cryoprobe layout is feasible. This study demonstrates that the training quality is essentially related to the training exposure time, rather than to a specific planning strategy from those investigated.

A medial axis based method for irregular grain shape representation in DEM simulations

This paper describes a novel method for representing arbitrary grain shapes in discrete element method (DEM) simulations. The method takes advantage of the efficient sphere contact treatment in DEM and approximates the overall grain shape by combining a number of overlapping spheres. The method is based on the medial axis transformation, which defines the set of spheres needed for total grain reconstruction. This number of spheres is then further diminished by selecting only a subset of reconstructing spheres and opting for a grain approximation rather than a full grain reconstruction. The effects of the grain approximating parameters on the key geometrical features of the grains and the overall mechanical response of the granular medium are monitored by an extensive sensitivity analysis. The results of DEM quasi-static oedometric compression on a granular sample of approximated grains exhibit a high level of accuracy even for a small number of spheres.

Directed Migration of Microscale Swimmers by an Array of Shaped Obstacles: Modeling and Shape Optimization

Achieving macroscopic directed migration of microscale swimmers in a fluid is an important step towards utilizing their autonomous motion. It has been experimentally shown that directed motion can be induced, without any external fields, by certain geometrically asymmetric obstacles due to interaction between their boundaries and the swimmers. In this paper, we propose a kinetic-type model to study swimming and directional migration of microscale bimetallic rods in a periodic array of posts with non-circular cross-sections. Both rod position and orientation are taken into account; rod trapping and release on the post boundaries are modeled by empirically characterizing curvature and orientational dependence of the boundary absorption and desorption. Intensity of the directed rod migration, which we call the normalized net flux, is then defined and computed given the geometry of the post array. We numerically study the effect of post spacings on the flux; we also apply shape optimization to find better post shapes that can induce stronger flux. Inspired by preliminary numerical results on two candidate posts, we perform an approximate analysis on a simplified model to show the key geometric features a good post should have. Based on that, three new candidate shapes are proposed which give rise to large fluxes. This approach provides an effective tool and guidance for experimentally designing new devices that induce strong directed migration of microscale swimmers.

Solid barriers for windblown sand mitigation: Aerodynamic behavior and conceptual design guidelines

Protection from windblown-sand is one of the key engineering issues for construction and maintenance of human infrastructures in arid environments. In the last century, several barriers with different shapes have been proposed in order to overcome this problem, but literature lacks of a systematic performance quantitative analysis, and the key geometric parameters that promote sedimentation have not been yet recognized. A deep understanding of the aerodynamics effects of sand barrier on the flow is an unavoidable step to achieve these objectives. The present computational study aims to comparatively analyze different kinds of windblown sand mitigation solid barriers, clarify their working principles, extract from the aerodynamics analysis key geometrical features of the barriers and relate them to the sand trapping performances. Approximated metrics for performance assessment are introduced using aerodynamic parameters. The performances of an innovative solid barrier and the ones of commonly used solid barriers are compared in terms of these metrics. The effects of incoming wind velocity profiles on sand trapping performances are evaluated as well. An empirical dimensionless performance estimator is proposed and used to provide general design guidelines.

Quality Inspection System of Circular Saw Blades Based on Eddy Current Inspection and Laser Measurement

Aiming at the problem of the complicated process, the low precision and efficiency of crack detection and key geometric feature of the circular saw blade, the quality detection system of the circular saw blade based on the nondestructive testing and laser measurement technology is studied. By using the laser measurement technology and optimizing the data processing method, the face runout, the thickness of the circular saw blade are measured. The crack defects in the tooth root region of the circular saw blade are detected by eddy current nondestructive testing technology. The system achieves the radial detection of 1mm radial sawing, the detection accuracy of the round beating is> 0.03mm, and the thickness measurement accuracy is> 0.005mm.

Computational study to investigate effect of tonometer geometry and patient-specific variability on radial artery tonometry

Tonometry-based devices are valuable method for vascular function assessment and for measurement of blood pressure. However current design and calibration methods rely on simple models, neglecting key geometrical features, and anthropometric and property variability among patients. Understanding impact of these influences on tonometer measurement is thus essential for improving outcomes of current devices, and for proposing improved design. Towards this goal, we present a realistic computational model for tissue-device interaction using complete wrist section with hyperelastic material and frictional contact. Three different tonometry geometries were considered including a new design, and patient-specific influences incorporated via anthropometric and age-dependent tissue stiffness variations. The results indicated that the new design showed stable surface contact stress with minimum influence of the parameters analyzed. The computational predictions were validated with experimental data from a prototype based on the new design. Finally, we showed that the underlying mechanics of vascular unloading in tonometry to be fundamentally different from that of oscillatory method. Due to directional loading in tonometry, pulse amplitude maxima was observed to occur at a significantly lower compression level (around 31%) than previously reported, which can impact blood pressure calibration approaches based on maximum pulse pressure recordings.

Development of decoupled multi-physics simulation for laser lap welding considering part-to-part gap

Remote laser welding is increasingly being adopted within the automotive industry due to its high production throughput at lower cost and flexibility, making the welding process much faster and more accurate. However, a leading challenge preventing its systematic uptake in the industry is the lack of efficient in-process monitoring and assuring high weld quality in the presence of process variability. Weld quality is generally assessed by measuring the key geometrical features of the melt pool such as penetration depth, interface width; and, both upper and bottom concavity which are directly correlated to static and fatigue performance. Existing solutions extract patterns from real-time data such as: plasma charge, acoustic or optical emissions measurements, etc. and integrate multivariate statistics and machine learning algorithms to estimate only a single key geometrical feature of the weld. For example, acoustic or optical emissions provide molten pool oscillation frequency, leading to penetration depth; the dimension of the molten pool obtained by visual sensing with high speed camera is correlated to interface width. The lack of comprehensive multiphysics models linking monitoring data and multiple welding process parameters (i.e. laser power, welding speed, and focal offset) with multiple key geometrical features underscores the limitations of the current methods toward delivering automatic in-process closed-loop quality control system. The multiphysics model should have capabilities for monitoring multiple key geometrical features; and, capabilities for on-the-fly process adjustment to guarantee high quality weld. This paper presents a novel analytical physics-driven simulation approach to monitor multiple key geometrical features. The developed model has the capability to be used for in-process monitoring of key geometrical features and, furthermore is a necessary enabler for the development of in-process closed-loop process adjustment applicable for remote laser welding. The proposed method is applicable for in-process monitoring of zinc coated steel in overlap joint configuration considering part-to-part gap.

Saccades to Explicit and Virtual Features in the Poggendorff Figure Show Perceptual Biases.

Human participants made saccadic eye movements to various features in a modified vertical Poggendorff figure, to measure errors in the location of key geometrical features. In one task, subjects (n = 8) made saccades to the vertex of the oblique T-intersection between a diagonal pointer and a vertical line. Results showed both a small tendency to shift the saccade toward the interior of the angle, and a larger bias in the direction of a shorter saccade path to the landing line. In a different kind of task (visual extrapolation), the same subjects fixated the tip of a 45° pointer and made a saccade to the implicit point of intersection between pointer and a distant vertical line. Results showed large errors in the saccade landing positions and the saccade polar angle, in the direction predicted from the perceptual Poggendorff bias. Further experiments manipulated the position of the fixation point relative to the implicit target, such that the Poggendorff bias would be in the opposite direction from a bias toward taking the shortest path to the landing line. The bias was still significant. We conclude that the Poggendorff bias in eye movements is in part due to the mislocation of visible target features but also to biases in planning a saccade to a virtual target across a gap. The latter kind of error comprises both a tendency to take the shortest path to the landing line, and a perceptual error that overestimates the vector component orthogonal to the gap.

Supercritical CO2 Radial Turbine Design Performance as a Function of Turbine Size Parameters

Supercritical CO2 (sCO2) cycles are considered as a promising technology for next generation concentrated solar thermal, waste heat recovery, and nuclear applications. Particularly at small scale, where radial inflow turbines can be employed, using sCO2 results in both system advantages and simplifications of the turbine design, leading to improved performance and cost reductions. This paper aims to provide new insight toward the design of radial turbines for operation with sCO2 in the 100–200 kW range. The quasi-one-dimensional mean-line design code topgen is enhanced to explore and map the radial turbine design space. This mapping process over a state space defined by head and flow coefficients allows the selection of an optimum turbine design, while balancing performance and geometrical constraints. By considering three operating points with varying power levels and rotor speeds, the effect of these on feasible design space and performance is explored. This provides new insight toward the key geometric features and operational constraints that limit the design space as well as scaling effects. Finally, review of the loss break-down of the designs elucidates the importance of the respective loss mechanisms. Similarly, it allows the identification of design directions that lead to improved performance. Overall, this work has shown that turbine design with efficiencies in the range of 78–82% is possible in this power range and provides insight into the design space that allows the selection of optimum designs.

The influence of mechanical constraints introduced by β annealed microstructures on the yield strength and ductility of Ti-6Al-4V

Discussed is a computational study of the influence of the microstructure’s geometric morphology on the yield strength and ductility of Ti-6Al-4V. Uniaxial tension tests were conducted on physical specimens to determine the macroscopic yield strength and ductility of two microstructural variations (mill annealed and β annealed) to establish comparisons of macroscopic properties. A multi-experimental approach was utilized to gather two dimensional and three dimensional data, which were used to inform the construction of representative β annealed polycrystals. A highly parallelized crystal plasticity finite element framework was employed to model the deformation response of the generated polycrystals subjected to uniaxial tension. To gauge the macroscopic response’s sensitivity to the morphology of the geometry, the key geometrical features - namely the number of high temperature β phase grains, α phase colonies, and size of remnant secondary β phase lamellae - were altered systematically in a suite of simulations. Both single phase and dual phase aggregates were studied. Presented are the calculated yield strengths and ductilities, and the resulting trends as functions of geometric parameters are examined in light of the heterogeneity in deformation at the crystal scale.