Geometrical Defects Research Articles

Effects of adherends’ misalignment on the 3-point flexural strength of single lap bonded joints

The adhesive joints are widely used in many industrial applications due to their advantages, such as a more uniform distribution of loads, a lighter weight, and greater fatigue properties compared to the traditional mechanical joints. One of the simplest methods of bonding two sheets is a single-lap bonded joint (SLJ). This work aims to investigate how the adherends’ misalignment influences the 3-point flexural strength of adhesive single-lap joints. This misalignment is due to the geometrical defects of the equipment used to bond them. It was developed a numerical model that was validated by some experimental tests.

On the Total Reflectivity Estimation of Microwave Calibration Targets by Backscattering Measurements

Before practical usage in microwave radiometers, the calibration targets must be tested for its emissivity/total reflectivity. In this work, we address the issue that remains in the total reflectivity determination, which is estimating the total reflectivity based on measured backscattering in the monostatic configuration, specifically at high frequencies. Based on the efficient modeling on periodic unit of the array-shaped calibration target, we quantitatively evaluate the relationship between backscattering and the total reflectivity, on the common structure of coated cones and coated pyramids. It is found that the total reflectivity estimation becomes target-specific for the coated cones; meanwhile, stable compensation can be concluded for the pyramidal units, which is important for practical testing in submillimeter applications. Then, the disturbing effects of the geometric defects on the total reflectivity estimation are discussed, and it is inferred that wideband measurement is vital for diagnosing those defects. Furthermore, actual test results are analyzed, showing the complex scenario in estimating the total reflectivity of a prototype with shape defects. Also, the numerical concluded <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$C_{g}$ </tex-math></inline-formula> compensation is verified in the clear case of a fine prototype. The findings in this work offer a direct reference for the application of microwave radiometer calibration, especially in the region of submillimeter waves.

Effect of printing parameters on microscale geometry for 3D printed lattice structures

This study investigated the effect of manufacturing parameters on the manufacturing quality of material extrusion additive manufacturing (MEAM), specifically focusing on the microscale geometry of lattice structures built up by discrete extruded filaments. The manufacturing parameters extrusion height, printing speed and extrusion width were investigated. Square grid structures, which can be precisely characterized, were used to develop fundamental understanding that can be translated to more complicated structures in future investigations. Print paths were directly created as machine control code (GCode) using FullControl GCode Designer, bypassing the conventional multi-stage translation of a design from CAD to an STL file, to slicing software and finally to GCode. This allowed precise parametric control of all aspects of the manufacturing procedure, including aspects that would not be possible with conventional slicing software such as control over the specific order and direction of printing each line, and the offsetting of specific printed lines on each layer in the Z direction by half the layer height. The printing quality of the structures was investigated with optical microscope and X-ray micro-computed tomography (micro-CT). Microscale changes to the extruded-filament geometry were characterized before and after filament-crossing points in the square grid structure, and internal cavities were identified. Printing speed was found to be a crucial parameter that should be carefully considered for lattice structure applications that require high manufacturing quality in terms of minimizing microscale geometric defects. Offsetting crossing extrudates by half the layer-height in the Z direction resulted in more consistent microscale geometry and greatly improved quality.

Wasserstein generative adversarial networks for form defects modeling

Geometric deviations of mechanical products are specified by tolerancing in the design stage for a functional purpose. In order to verify the impact of geometric deviations on functional surfaces while considering the manufacturing process, form defects have been considered in tolerance analysis in recent years. As a digital representation of geometrical defects in mechanical parts and assemblies, Skin Model Shapes enables the rapid and comprehensive generation of non-ideal shapes from either measurement or via data augmentation using simulation approaches. This paper presents a novel method for form defects modeling using Generative Adversarial Networks (GAN). The form defects of cylindrical surfaces considering machining process are represented and used for training a Wasserstein GAN. The pre-trained network is able to generate realistic form defects for cylindrical Skin Model Shapes rapidly and automatically without explicitly formulated representations. Manufacturing errors in turning process are considered in this approach and the generated samples from WGAN can be re-used for generating new cylindrical surfaces with a mapping strategy considering specification. A case study of a cylindricity specification is used in the paper to illustrate the effectiveness of the proposed method.

Analysis of Mmm Signal for the Coexistence of Geometric Defects and Fatigue Stress at the Same Location

Analysis of Mmm Signal for the Coexistence of Geometric Defects and Fatigue Stress at the Same Location

Compressive properties of imperfect Ti-6Al-4V lattice structure fabricated by electron beam powder bed fusion under static and dynamic loadings

Mechanical response and deformation behavior of Ti-6Al-4V lattice structure are investigated by quasi-static and low-speed impact compression experiments. The lattice specimens with SC-BCC-FCC cells are designed and fabricated by electron beam powder bed fusion (EB-PBF). The nominal stress-strain and stress-time histories of the printed lattice structures under different loading speeds are determined by an electronic universal testing machine and a drop hammer system, respectively. The corresponding global collapse evolution of the specimens is recorded and analyzed. Meanwhile, the high-resolution scanning electron microscope (SEM) and X-ray computed tomography (CT) are adopted to capture the morphology, occurrences, and distributions of the geometric defects induced by the printing process. Based on the distribution characteristics of the defects, a novel statistical finite element model is proposed by considering the strut waviness and thickness variation to predict the mechanical performance and reveal the detailed deformation mechanism of the lattice. A good agreement is obtained between the statistical model predictions and experimental results. Furthermore, the role of each geometric defect on the initial peak stress of the lattice is investigated. The results demonstrate that the strut thickness variation in the lattice structure presents a more significant influence on initial peak stress than the strut waviness under quasi-static and low-speed impact loadings.

Hyper‐viscoelastic characterization of highly filled rubber compound: Extending approach for geometrical defect analysis

AbstractThe work provides insight into the hyper‐viscoelastic characterization of highly filled rubber compound with low structured carbon black, further examining geometrical defects using finite element (FE) simulations. The complete force‐extension behavior and stress relaxation (various strain levels [10%–100%]) in a uniaxial state of stress are reported. The extension at break is reduced by more than 42% for geometrically defective specimens. The breakage of filler–filler interaction attains equilibrium at 75% strain in stress relaxation experiment. Beyond this, the relaxation depends majorly on polymer chains. Hyperelastic material models, namely Ogden, Yeoh, and Arruda–Boyce, are chosen for the present investigation. A Prony series is used for capturing the viscoelastic properties of relaxation times. The combined utilization of the Ogden law and the Prony series in FE simulations provides an excellent match in capturing the experimental features. The effect of geometrical defects is illustrated via solving a series of numerical as well as experimental results. The simulated shape/profile changes such as necking and elliptical formation are excellently comparable with experimental results. Strain localization study shows the stress concentration zone and early prediction of failure location. The methodology presented is potentially crucial for understanding and simulating engineering rubber product's complex structures in general.

Ultrasound in situ characterization of hybrid additively manufactured Ti6Al4V.

A major barrier for the full utilization of metal additive manufacturing (AM) technologies is quality control. Additionally, in situ real time nondestructive monitoring is desirable due to the typical high value and low volume of components manufactured with metal AM. Depending on the application, characteristics such as the geometrical accuracy, porosity, defect size and content, and material properties are quantities of interest for in situ nondestructive evaluation (NDE). In particular, functionally tailored components made with hybrid processing require quantitative NDE of their microstructure and elastic properties. Ultrasonic NDE is able to quantify these relevant characteristics. In this work, an ultrasonic measurement system is used to collect in situ real time measurements during the manufacturing of samples made with a hybrid process, which combines directed energy deposition with milling. In addition to quantifying ultrasonic properties, the measurements are used to gather insight on other geometry, material, and process effects. The results show the utility of ultrasound to evaluate relevant properties during manufacturing of a functionalized material domain, while providing perspective on additional material evolution information obtained from ultrasonic signals.

Improving the efficiency of machining on metal-cutting machines by aligning the CNC program and the evolutionarily changing cutting dynamics

Modern machines with high accuracy provide an accordance of the trajectories of the executive elements to the CNC program. However, this is not guarantee the same accuracy of manufacturing the part. One of the main reasons for the formation of the geometric defects is the elastic deformations of the tool and the workpiece. It is caused by variations of the cutting forces, changes in the rigidity of the workpiece along the tool path. It depends on changes of the properties of the dynamic link formed by cutting. Therefore, there is a problem of synergetic aligning of controlled trajectories with changing cutting properties. In the article, the regularities of the alignment of external control and internal dynamics are considered on the basis of mathematical modeling of the system in which the trajectories of the executive elements are controlled. The case of accounting the a priori given law of changes of the stiffness of the workpiece is considered. The effectiveness of the alignment is estimated by the reduced costs while ensuring the required quality of the parts.

Geometry optimization for tunable band gap and wave guiding in periodic grid structures

A proper lattice structure consisting of homogeneous material is designed in this paper to investigate the maximum bandwidth of perfect lattice structures and tunable property of waveguide with linear geometric defect by means of selecting optimal geometric lattice cell. A simulation model based on finite element method is used to calculate dispersion curves and transmission spectrums of lattice structures with different geometric parameters. Meanwhile, a simplified theoretical model of unit cell, which considers the mass of grid bar and stiffness of node area, is applied to validate the accuracy of simulation result and may provide an effective approach for prediction of band gap lower boundary. Then, the validated numerical results show different orders of widest band gap that can be realized by different optimal geometric structures. Moreover, waveguide property can be effectively controlled and manipulated by changing defect parameters. The present study may establish theoretical and simulation foundation to control and manipulate band structures and other acoustic propagation characteristics of waveguide devices.

Mobile robot with failure inspection system for ferromagnetic structures using magnetic memory method

Flaws or cracks are one of the major failures in oil and gas pipeline networks. The early detection of these failures is very important for the safety of the industry, and this last requires of analysis for non-destructive testing (NDT), which is reliable, inexpensive and easy to implement. In this paper, we propose the development of an embedded prototype mounted on a mobile robot for the inspection of defects in ferromagnetic plates. This prototype has two embedded systems (control and data acquisition), which are based on a microcontroller of 8 and 32 bits, respectively. On the one hand, the first system for control has the logic to govern the sensors and motors that will allow to the robot moves with autonomous way during 45 min. While, the second system presents an algorithm for storing, processing and sending the data obtained from the sensors, being able to measure variations in the magnetic field in the order of 0.1 µT. Magnetic-field reading tests have been carried out on control ASTM A-27 ferromagnetic plates, obtaining experimental response in the 3 axes of the magnetic domains, which is very close to the expected results by the magnetic-flux density model that is calculated from the fields E and B derived from the equations of a Hertz dipole, and developed in the high-level Python programming language. The prototype proposed for NDT can detect geometric defects in the range of millimeters, producing changes in the density of the magnetic field in the order of thousands of µT.

Study of geometrical defects of free-form surface machined using neural network

The manufacture of total hip arthroplasty (THA) requires the control of the quality of free form surfaces. In fact, the polyethylene insert is deformed to fit the overall geometry of the femoral part, which has an impact on the quality of the contact. In this paper, we propose a method for evaluating the defects of complex forms. The originality of the approach is the use of artificial intelligence to position the cloud of measured points, obtained with a three-dimensional measuring machine equipped with a contactless sensor, with regard to the 3D CAD model of the THA. The artificial intelligence algorithm used is based on neural networks that are trained using a virtual positioning realized with 3D CAD software. Finally, the difference between the positioned point cloud and the CAD model allows us to evaluate the shape defect of the measured THA surface. We found that the error of the proposed method is at the vicinity of micron scale.

ЗАСТОСУВАННЯ НЕЙРО-НЕЧІТКИХ МЕРЕЖ ДЛЯ ВИЗНАЧЕННЯ РАЦІОНАЛЬНИХ ПАРАМЕТРІВ ЧИСЕЛЬНОГО РОЗВ’ЯЗКУ СИСТЕМ ДИФЕРЕНЦІАЛЬНИХ РІВНЯНЬ

Purpose. The purpose of the work is to improve the computational methods of calculating the systems of differential equations, which describe the accumulation of geometrical defects of structures, which function in an aggressive environment. Obtaining a numerical result with predetermined flexibility requires numerical integration parameters that would ensure the required accuracy. Methodology. The calculation costs of solving the problem of predicting the lon-gevity of corrosive structures are related to this system of differential equations. In cases where the problem of optimal design is solved, then the selection of optimal parameters of numerical procedures with control over the accuracy be-comes essential. To improve the efficiency of computational methods for this class of differential equation systems, the work is suggested to use elements of the computational intellect, which are neural networks. It is suggested to use an adaptive neural network for obtaining parameters of numerical integration on the basis of fuzzy logical inference, which allows formalizing the multidimensional data used for setting up a fuzzy system. Results. This approach allows using a neuro-fuzzy network for forecasting the durability timeframe taking into account the parameters that influence it. Orig-inality. The results of numerical experiments show that the adaptive neuro-fuzzy system after the training is able to summarize the input data and propose the parameters of numerical procedures, which ensure the required accuracy of the obtained result. Numerical experiments based on the comparison of reserved data and results of network operation prove that the adaptive system can be used to improve the efficiency of calculating methods when carrying out this type of task. References 21, tables 2, figures 2.

Cyclic response of 3D printed metamaterials with soft cellular architecture: The interplay between as-built defects, material and geometric non-linearity

The paper investigates the cyclic response of soft cellular materials undergoing repeated local instabilities. Our focus is mainly on the coupling between material non-linearities, geometric non-linearity as well as defects induced by 3D printing. Two paradigmatic lattices (triangular and hexagonal), each with its own distinct deformation mode and defect sensitivity, are examined, and the emergence of as-built material and geometric defects in the form of microporosity, strut thickness reduction, and nodal dispersion is studied via computed tomography and optical analyses. Experiments are carried out on the base material and lattice specimens for given cycling strains and cycle ratios. Numerical models are developed to understand the individual role of the main constitutive aspects of the base material, e.g. damage, creep, and visco-elasticity, as well as to assess the role of defects in each architecture. The results show that the activation of local buckling combined with the engagement of material non-linearities has multiple outcomes. It leads to local storage of inelastic strain, which in turn perturbs the lattice geometry after the second cycle and severely impacts the subsequent response, e.g. softening; it reduces the tangent modulus at zero strain; and it also decreases the maximum and minimum cyclic stresses. The detriment is further fueled by geometric deviations caused by 3D printing. Furthermore, a theoretical model is presented to obtain stress bound estimates of the stabilized response, hence offering guidelines for the design of 3D printed soft metamaterials under cycling loading. The paper concludes with a systematic discussion on the coupled role of non-linearities (material and geometry) and defects, and on the accuracy of the numerical and theoretical models herein presented.

In-depth understanding of material flow behavior and refinement mechanism during bobbin tool friction stir welding

Bobbin tool friction stir welding (BT-FSW) is a promising solid-state welding process for fabricating closed or hollow profiles due to its self-supporting nature, which is achieved using a combined tool consisting of two shoulders and a penetrating pin, releasing the backing plate. The joint reliability is mainly affected by its macro-/micro-features including geometric defects and non-uniform grains. However, the underlying thermo-physical process has not been fully understood to clarify how the defects form and grains evolve during welding and how to control them. In this paper, a 3D thermo-mechanically coupled Eulerian-Lagrangian model was developed to analyze the material flow behavior and help understand the defect forming mechanism and recrystallization behavior during BT-FSW of aluminum alloy, wherein tracing particles were specially embedded. The calculated results revealed a complex material migration in the domain driven by the rotating tool. The flow behavior in horizontal/vertical directions at local regions was asynchronous, and eventually converged on the advancing side (AS) to normally form a sound joint, where the combined effects of shearing and squeezing of the material flow throughout thickness affected the morphology of S-line defect. In addition, the non-uniform thermo-mechanical cycling caused an abrupt change in grain structure near the TMAZ/SZ-AS transition region due to the combined continuous and discontinuous dynamic recrystallization, and geometrical effect of strain. The final joint failure was the result of competition between the two softening regions, S-line defect and TMAZ/SZ-AS. These can be applied for further fundamental investigation of parameter optimization or welding structure design, and promote the exploration of post-processing methods to improve the joint performance.

Geometrical Frustration and Defect Formation in Growth of Colloidal Nanoparticle Crystals on a Cylinder: Implications for Assembly of Chiral Nanomaterials

Geometrical Frustration and Defect Formation in Growth of Colloidal Nanoparticle Crystals on a Cylinder: Implications for Assembly of Chiral Nanomaterials

The influence of geometric defects and microstructure in the simulation of the mechanical behaviour of laser powder-bed fusion components: Application to endoprosthesis

This work aims at enabling the fabrication of a new generation of prosthetic components with enhanced mechanical behaviour and an extended lifetime. Cobalt‑chromium lattice structures manufactured using laser powder bed fusion are analysed to quantify the influence of microstructural anisotropy and geometrical deviations on stiffness prediction. Results of the experimental campaign are used to improve finite-element modelling of the mechanical behaviour of functionally graded lattice structures. The proposed method, which can be extended to any lattice structure fabricated by laser powder bed fusion, is then used to redesign an ankle prosthetic component.

Assessment of wind-induced fragility of transmission towersunder quasi-static wind load

Overhead power transmission line systems consisting of long-span conductors and high-rise towers are wind-sensitive structures featured with significant structural nonlinearity and fragility under wind hazards. To assess wind-induced structural fragility of a transmission tower, a novel efficient quasi-static approach, which is based on the analytical probability distribution of extreme wind effect in frequency domain and the probabilistic wind-resistant capacity, is developed in the present study. The 90-degree wind direction (perpendicular to conductors), which is always the worst scenario, is considered in this paper. The structural nonlinearity and failure modes are captured using a nonlinear static push-over analysis method, which simulates the failure process of the tower structure with random initial geometric defects. Wind-resistance performance of the tower is quantified based on the principle of energy equivalence. Damage of the tower is classified into three levels including slight damage, severe damage, and collapse. The tower fragility curve, which predicts damage of the tower as a function of wind speed, is presented and discussed.

Assessment of the global stability of three-limbed steel tube latticed column using finite element modelling

In order to study the stability performance of the three-limbed steel tube latticed column, the finite element numerical analysis method based on the structural stability theory is adopted. Firstly, the linear analysis of the three-limbed steel tube latticed column without diagonal lacing bar is carried out, and the calculation method of elastic buckling load considering the influence of shear deformation is obtained. Then, the elastic buckling analysis and elastoplastic buckling analysis three-limbed steel tube latticed column with diagonal lacing bar are carried out. The elastic buckling load and elastoplastic buckling load of three-limbed steel tube latticed column with diagonal lacing bar are studied when only the global initial geometric defects, only the member initial geometric defects, and both kinds of defects are considered at the same time. The results show that the direct finite element analysis method can be used to calculate the elastic buckling load of three-limbed steel tube latticed column with diagonal lacing bar, and the error is 6.67%. In the elastic analysis of three-limbed steel tube latticed column with diagonal lacing bar, the column global stability mainly depends on the global initial geometric defects, and the member initial geometric defect is negligible. And when two kinds of defects are applied at the same time, the structural buckling load is reduced by less than 0.20% compared to the global initial geometric defects. In the elastoplastic analysis, the column global stability is determined by both the global initial geometric defect and the member initial geometric defect. When both defects are applied at the same time, the structural buckling load decreases by less than 0.65% compared to the global initial geometric defect only, and 7.60% compared to the member initial geometric defects only. It can be concluded that there is little difference in the overall stability bearing capacity between the two kinds of defects.

Analysis of robotic welding possibilities of a car chassis assembly

The continuous increase of the requirements regarding the quality of the welded joints (elimination of the influence of the human factor) but also the increase of the productivity of the technological processes imposed the analysis of the possibilities of implementing robotic welding processes. The introduction of robotic production lines is an increasingly common thing in the automotive industry. This paper presents the stages necessary for the realization in welded construction of a crossbeam, part of the chassis of a car. The elaborated welding technology aimed to achieve the transition from semi-mechanized welding of the assembly to robotic welding using the MAG (Metal Activ Gas) welding process. The basic material from which the crossbar is made is S355 MC steel, steel for constructions with high mechanical properties. For the robotic welding of the assembly, the design of the device necessary for the orientation and fixing of the components was made. The welding technology developed was validated by performing standard samples that were subjected to visual examination and penetrant testing but also to destructive examinations which consisted in measuring the hardness in the characteristic points of the welding bead and also by measuring its geometric characteristics. Following the analysis of the initial dimensional values obtained, it resulted that the incorrect positioning of the welding head in relation to the welded components led to the appearance of geometric defects of the welding seams, although the technological parameters of the welding regime were appropriate. After making adjustments on the position of the welding head, accepted characteristics were obtained which led to the decision to validate the welding technology used.