Complex Contact Research Articles

Process-independent construction stage analysis of self-anchored suspension bridges

The construction process of self-anchored suspension (SAS) bridges undergoes frequent system transformations and loadings, accompanied by complex strong geometric and contact nonlinear behaviours. The accurate state assessment of such a process generally requires the nonlinear finite element analysis (FEA) to perform a stage-by-stage forward, cumulative calculation based on the principle of incremental superposition. This sort of calculation means that the structural equilibrium of any intermediate state of the process, referred to as a construction stage, must be accumulated from its previous construction loading history, which is susceptible to computational effort and divergence limitations. This paper overcomes these limitations by proposing a direct and fast method that is independent of the cumulative calculation in the analysis of any specified construction stage, in favour of the construction optimization design and uncertainty analysis. The unstrained assembly formats for the typical construction process of SAS bridges are established, and the elements with constant physical quantities as the characteristic parameters are used to describe the various structures, boundaries, loads and their changes during the construction. On this basis, an interactive analysis framework integrating the numerical iteration with the FEA is established to achieve an accurate equilibrium for the construction stages. An enhanced interval-genetic algorithm (IGA) is employed as the optimization engine to smoothly accelerate global convergence. The proposed framework is applied to an SAS bridge under construction, and the validity and performance of this approach are demonstrated by considering the in-field test data.

Strength analysis of the interference joint of the oval submarine pipeline to the mechanical connector

For damaged submarine pipelines, interference fit is necessary for the mechanical connector repair. The ovality of pipelines resulting from the fabrication errors is easy to increase the failure risk during the fit process. In order to ensure the construction safety, it is necessary to judge whether the repair process may be affected by the strength damage in advance. Since the interference joint with ovality is a complex nonlinear contact problem, there is no theoretical model for reference at present. Reasonable and verified numerical simulation has been proved to be a convenient and feasible solution. In this paper, the finite element (FE) software ANSYS was used to analyze the contact characteristics of the pipeline coupled with the theory of combined thick-wall cylinder. The influences of the equivalent interference and pipeline ovality on the maximum effective stress of the pipeline were quantitatively characterized, and the corresponding correlation model was fitted. The results show that the contact stress of pipeline is closely related to the equivalent interference, the ovality hardly effects it but has a significant effect on the uniformity of the contact stress distribution on the interference surface. Furthermore, according to the theoretical solution, the prediction model of the equivalent stress of pipeline is deduced with an introduced ovality stress concentration coefficient. The prediction model can effectively evaluate the strength of the submarine pipeline after interference repair. The rationality and practicability of this method are validated by simulation analysis of a practical engineering project.

A physics-based and data-driven hybrid modeling method for accurately simulating complex contact phenomenon

Traditional physics-based contact models have been widely used for describing various contact phenomena such as robotic grasping and assembly. However, difficulties in carrying out contact parameter identification as well as the relatively low measurement accuracy due to complex contact geometry and surface uncertainties are the limiting factors of the physics-based contact modeling methods. In this paper, we present a novel hybrid contact modeling (HCM) method as an endeavor to discover models that can more accurately simulate practical contact scenarios than traditional physics-based contact models. The proposed method is implemented by combining a physics-based contact model and a data-driven error model. This approach is validated by using simulations of a bouncing ball, a flat-shot, and a three-dimensional (3D) peg-in-hole. The results demonstrate the feasibility and consistent performance of the HCM method.

Investigation of parametric control method and model in abrasive belt grinding of nickel-based superalloy blade

Abrasive belt grinding is gradually recognized as an effective machining technology for blade. However, the complex contact characteristics of this technology make the grinding quality of blade unable to be precisely controlled. In order to solve this problem, a parametric control method for precision abrasive belt grinding of blade was proposed, and a multi-parameter test platform for state parameters (grinding force, vibration, and temperature) was established. The grinding experiments of nickel-based superalloy samples were carried out, and the prediction model of state parameters based on back propagation neural network was constituted. The prediction accuracy of the model was 93.58%. On this basis, the grinding experiments of nickel-based superalloy blade were conducted. The influence of state parameters on the evaluation parameters (material removal, profile accuracy, surface quality) was analyzed and the optimal grinding parameters were determined. The experimental results showed that the machining quality of new-type aeroengine blades can be effectively improved by this parametric control method and model.

Model accelerated reinforcement learning for high precision robotic assembly

Peg-in-hole assembly with narrow clearance is a typical robotic contact-rich task in industrial manufacturing. Robot learning allows robots to directly acquire the assembly skills for this task without modeling and recognizing the complex contact states. However, learning such skills is still challenging for robot because of the difficulties in collecting massive transitions data and transferring skills to new tasks, which inevitably leads to low training efficiency. This paper formulated the assembly task as a Markov decision process, and proposed a model accelerated reinforcement learning method to efficiently learn assembly policy. In this method, the assembly policy is learned with the maximum entropy reinforcement learning framework and executed with an impedance controller, which ensures exploration efficiency meanwhile allows transferring skills between tasks. To reduce sample complexity and improve training efficiency, the proposed method learns the environment dynamics with Gaussian Process while training policy, then, the learned dynamic model is utilized to improve target value estimation and generate virtual data to argument transition samples. This method can robustly learn assembly skills while minimizing real-world interaction requirements which makes it suitable for realistic assembly scenarios. To verify the proposed method, experiments on an industrial robot are conducted, and the results demonstrate that the proposed method improves the training efficiency by 31% compared with the method without model acceleration and the learned skill can be transferred to new tasks to accelerate the training for new policies.

Full-scale finite element analysis of deformation and contact of a wire-wrapped fuel bundle subject to realistic thermal and irradiation conditions

The fuel bundle in a fast breeder reactor (FBR) is wrapped with wires for guiding the flow of liquid metal. Under operation condition with irradiation and high temperature, the wrapped bundle undergoes complex contact so that the flow channel of liquid will be affected. There are mainly four factors involved: radiation swelling, thermal expansion, radiation creep and thermal creep. In the present study, a full-scale finite element model (FEM) is established to consider the effect of these factors on the complex contact during operation. The established model can capture the contact separation, spacer wire’s dispersion, oval distortion and bowing details of fuel pins. The results show that the local contact dispersion caused by the wire slip can alleviate the severe transverse bending deformation of the bundle. What is more important, we find out that the dispersion of contact points in the peripheral direction of the bundle is another key factor for alleviating the severe deformation of the bundle during operation, this new mechanism – peripheral dispersion of contact – has not been achieved in previous studies.

Study on the Mechanical Properties of Metal Rubber with Complex Contact Friction of Spiral Coils based on Virtual Manufacturing Technology

Metal rubber (MR) is an elastic porous material with a complex spiral network structure, which is widely used in aerospace, aviation, navigation, medical biomaterials, and other fields. The traditional preparation processes depend on multiple tests or artificial experience, which leads to time‐consuming and laborious. Herein, a virtual manufacturing method is proposed to realize the spatial multipoint dynamic contact analysis of a complex spiral network structure, that is, to study the mechanical properties of MR from the micro‐tribological point of view. Through real‐time capturing the spatial distribution characteristics of each contact point and the number of contact pairs and contact mode, it is found that the number of dry friction contact points between the wires is nonlinear positive correlation with the damping energy dissipation characteristics of MR. The preparation parameters, such as the wire diameter, the spiral wire pitch, and the blank winding angle, are selected to be investigated, and the controlling variable method is used to analyze the single factor influence in the virtual preparation process. The results show that the damping and energy consumption characteristics of MR can be improved effectively by reducing the wire diameter, by reducing the spiral wire pitch, or by increasing the winding angle of the blank. However, too small or too large preparation parameters cause stress concentration and affect the mechanical properties of the actual materials. The quasi‐static compression test is carried out through the preparation of the products, and the error between simulation and experiment results is <8%. Herein, the mechanism of contact friction between wire turns in MR is expounded. Also, this method can effectively guide the production of MR material, reduce the time of material design, and promote the popularization and application of the material.

Structural modeling of crossed roller wire race bearings: Analytical submodel for the roller-wire-ring set

Since wire bearings were patented in 1936, they have been used in applications where weight saving is a key aspect. Nevertheless, little work can be found in literature regarding their structural behaviour. In order to predict how a wire bearing reacts under load, the most feasible way is to model and analyse it via Finite Elements (FE). However, the great amount of elements needed to properly model the complex contact configuration among rollers, wires and raceways, make this approach unaffordable. In this sense, this manuscript develops an analytical submodel that represents the structural behaviour of the roller-wire-ring set, in order to include it later in a global FE model to account for ring flexibility and boundary conditions. This way, the computationally intensive FE modelling of these complex zones can be substituted by the analytical model developed in this work, and a much manageable global FE model can be used to predict the structural response of the bearing. This analytical model has demonstrated a good agreement with local FE models of the roller-wire-ring set.

Macro-meso dynamic analysis of railway transition zone: Hybrid DEM/FDM simulation and experimental validation

To probe into the mechanical behaviour of railway transition zone from the macro-meso aspects, a numerical model of transition zone is built that hybrids the Discrete Element Method (DEM) and Finite Difference Method (FDM). The DEM is utilised to simulate the ballast bed and sleeper, because it can consider the realistic ballast shapes and complex contacts between them. The FDM based on the continuum theory is utilised to simulate the track substructure according to a real structural form. Afterwards, the coupling algorithm is used to achieve the hybrid DEM-FDM simulation. The engineering practicality of this model is validated using the dynamic responses of the transition zone from a field measurement, and the macro-meso mechanical behaviour of the transition zone is analysed with or without the wedge-shape backfill. The numerical results indicate that applying the wedge-shape backfill can considerably reduce the sudden changes of track vibration and substructure surface stresses at the vicinity of the connection between the structure and embankment. Moreover, the mesoscopic results show that the acceleration vector of the soil near the rigid structure fluctuates towards the embankment and the velocity responses of track components and substructure increase gradually when the train travels from the rigid structure to the soft embankment.

Charge Interactions Modulate the Encounter Complex Ensemble of Two Differently Charged Disordered Protein Partners of KIX.

Disordered proteins play important roles in cell signaling and are frequently involved in protein-protein interactions. They also have a larger proportion of charged and polar residues than their folded counterparts. Here, we developed a structure-based model and applied molecular dynamics simulations to examine the presence and importance of electrostatic interactions in the binding processes of two differently charged intrinsically disordered ligands of the KIX domain of CBP. We observed non-native opposite-charged contacts in the encounter complexes for both ligands with KIX, and this may be a general feature of coupled folding and binding reactions. The ensemble of successful encounter complexes is a diverse set of structures, and in the case of the highly charged ligand, this ensemble was found to be malleable with respect to ionic strength. There are only minor differences between encounter complex ensembles for successful and unsuccessful collisions with no key interactions that appear to make the process far more productive. The energy landscape at this early stage in the process does not appear highly funneled. Strikingly we observed many native interactions that appear to reduce chances of an encounter complex being productive. Instead it appears that collectively non-native electrostatic interactions in the encounter complex increase the likelihood of productivity by holding the proteins together long enough for folding to take place. This mechanism is more effective for the more highly charged ligand.

A thermo-mechanical model of drill margin-borehole surface interface contact conditions in dry drilling of thick CFRP laminates

Dry drilling of thick carbon fiber reinforced polymer (CFRP) laminates requires careful selection of process parameters in order to obtain acceptable borehole surface quality. Complex contact conditions between the drill margin and the borehole surface determine the integrity of the borehole surface depending on the process parameters and temperature-dependent viscoelastic material properties. Temperature rise during dry drilling reduces the elastic modulus of the CFRP and causes thermal expansion of the drill, resulting in considerable contact length at the drill margin and borehole surface interface. Manufacturers need a better understanding of the interaction among contact pressure, sliding velocity, temperature at the interface, and temperature-dependent material properties to develop predictive models for drilling CFRPs. To examine this complex interaction, this study develops a novel, hybrid model that combines a time-based analytical modeling of drilling process with a finite element-based modeling of temperature rise. Drilling experiments were performed in which thrust force, torque, and temperature were measured as a function of feed, and these measurements were used to identify unknown hybrid model parameters. The results revealed that a significant change in friction conditions occurs when increased temperatures at the margin and borehole surface interface approach and exceed the glass transition temperature of the CFRP laminate at a large feed rate. These findings show the benefit of increasing feed during dry drilling, which is nonetheless limited by the temperature-dependent material properties of the work material.

The interactions between an off-road tire and granular terrain: GPU-based DEM-FEM simulation and experimental validation

Numerical methods have become useful tools for predicting vehicle mobility performance on granular terrain. However, due to the large number of soil particles and complex contact search in tire-granular terrain simulation, time-consuming calculation has become the most critical problem restricting the application of these methods. In this study, an efficient GPU-based DEM-FEM for simulation of the interactions between an off-road tire and granular terrain is implemented to improve computational efficiency. In this method, the main body of calculation is executed on GPU and programmed into an in-house developed code CDFP. The new GPU-based computing framework consists of 14 kernels, including efficient contact calculation between large-scale particles, novel contact calculation between particles and complex tread, contact calculation between particles and boundary wall, internal force calculation of finite elements, and information update. As a result, the efficient contact search and the complex interactions between an off-road tire and granular terrain are accomplished. Based on the self-developed single-wheel test device, an accurate simulation model consistent with the experiment is established. The validity of the proposed method is verified by comparing the simulation results with the experimental results. Finally, the discussion of computational efficiency shows that the proposed GPU-based DEM-FEM can be a powerful tool to simulate the interactions between an off-road tire and granular terrain.

Quantification of the silver content of a silver-plated nylon electrode according to the nature of the laundering detergent

In this study, the loss of the silver content was determined accurately when silver plated nylon electrodes dedicated to a measurement of human physiological parameters are washed with detergents containing bleaching agents. Thermogravimetric analysis and morphological observations based on SEM images have been conducted to determine the quantity of remaining silver on the electrodes. This loss of the conductive silver content is critical for the electrodes as it reduces their electrical conductivity and therefore their capacity to be used to measure either low voltages from the skin generated by ECG (electrocardiograph), EMG (electromyograph) or even EEG (electroencephalograph) or to determine the bioimpedance of human body or specific organs. The reduced surface conductivity leads also to a very complex contact impedance between the electrodes and the skin and therefore to their high sensitivity to any movement. This also results in noisy signals that are not useful to monitoring of physiological parameters and the concept of predictive medicine.

But Will It Build? Assessing Student Engineering Designers’ Use of Design for Additive Manufacturing Considerations in Design Outcomes

Abstract Additive manufacturing (AM) enables engineers to improve the functionality and performance of their designs by adding complexity at little to no additional cost. However, AM processes also exhibit certain unique limitations, such as the presence of support material. These limitations must be accounted for to ensure that designs can be manufactured feasibly and cost-effectively. Given these unique process characteristics, it is important for an AM-trained workforce to be able to incorporate both opportunistic and restrictive design for AM (DfAM) considerations into the design process. While AM/DfAM educational interventions have been discussed in the literature, few studies have objectively assessed the integration of DfAM in student engineering designers’ design outcomes. Furthermore, limited research has explored how the use of DfAM affects the students’ AM designs’ achievement of design task objectives. This research explores this gap in literature through an experimental study with 301 undergraduate students. Specifically, participants were exposed to either restrictive DfAM or dual DfAM (both opportunistic and restrictive) and then asked to participate in a design challenge. The participants’ final designs were evaluated for (1) build time and build material (2) the use of the various DfAM concepts, and (3) the features used to manifest these DfAM concepts. The results show that the use of certain DfAM considerations, such as part complexity, number of parts, support material mass, and build plate contact area (corresponding to warping tendency), correlated with the build material and build time of the AM designs—minimizing both of which were objectives of the design task. The results also show that introducing participants to opportunistic DfAM leads to the generation of designs with higher part complexity and lower build plate contact area but a greater presence of inaccessible support material.

Study on gear contact fatigue failure competition mechanism considering tooth wear evolution

Contact fatigue issues are becoming more prominent in current gear anti-fatigue designs. Surface wear may result in unavoidable occurrence competition among contact fatigue failure modes such as micropitting and pitting. This work proposed a model incorporating the interface characteristics, mechanical properties and residual stress gradients to explore this competition mechanism during wear process of a wind turbine gear pair. Results reveal that the critical damage position moves deeper from near-surface to subsurface during the wear process, indicating that the most likely failure mode changes gradually from surface initiated contact failure to subsurface initiated contact failure. This illustrates that one-sided gear anti-fatigue designs may not satisfy the complex contact conditions because the dominant failure mode may change during operation.

A frictional spring and cohesive contact model for accurate simulation of contact forces in numerical manifold method

Summary“Open‐close iteration” is a crucial algorithm for handling complex contacts in numerical manifold method (NMM) and discontinuous deformation analysis (DDA). This algorithm has proved to be robust and efficient for decades. However, as some researchers have pointed out, the original open‐close iteration may involve errors in sliding tests, especially in critical sliding tests with cohesive contacts. In this study, two major problems in the original algorithm are found to be nonconvergent contact force and early removed cohesive strength. The modifications are the following: (a) a frictional spring. By avoiding the trail value of normal contact force, we added a new frictional spring to the iteration scheme. This spring can apply accurate friction and can help ensure the convergence of contact forces. (b) A cohesive contact model. The original scheme can encounter an “early failure” in cohesive contacts. After investigating how contacts provide shear resistance, we found the cause and then provided a simple correction of the cohesive issue. The new algorithms in this article are essential for accurately simulating contacts by NMM/DDA.

Behavior and analytical investigation of assembled connection between steel beam and concrete encased CFST column

Concrete encased CFST (CECFST) column is a composite member consisted of outer encased concrete and inner CFST. Currently, a cast-in-place connection between a CECFST column and a reinforcement concrete beam is generally employed in engineering practice due to the outer encased concrete hinders the application of assembled connection, and the steel beam is usually connected to the CECFST column by on-site welding. In this paper, a novel on-site assembled connection between a CECFST column and a steel beam was proposed. In considering various material models and complex contacts, a FE model for this type of joint was established and verified. Further, parametric analyses of the assembled connections to concrete encased CFST columns were conducted to analyze the structural behavior. More importantly, an extended component model was developed to cover the feature of CECFST column focusing on the initial stiffness and moment resistance of the assembled connection. The load transfer mechanism for bolt in tension and beam flange in compression were considered in the modelling for evaluating the stiffness and strength of column wall in tension and in compression, respectively. The numerical results from the parametric analyses coincided well with the predicted results. The numerical and analytical results declared that this novel assembled connection between the CECFST column and steel beam performed favorable structural behavior and could be employed in assembled structures with CECFST columns.

Experimental and Analytical Behavior of Square CFDST Column Blind Bolted to Steel Beam Connections

In recent years, steel or composite beam-column connections adopting blind fasteners have drawn increasing praise due to the rapid development of assembled steel structures. However, limited researches have paid attention to the experimental and analytical behavior of concrete filled double-skin steel tube (CFDST) column blind bolted joints. For investigating the structural performance and seismic behavior of this type of connection, cyclic tests on blind bolted joints to square CFDST columns were carried out to explore the effects of column hollow ratio and end plate type. Finite element analytical modelling of the semi-rigid joint was performed considering complex contact interactions and material models. Good agreement between the test and analytical results was observed in terms of the failure modes and the hysteretic behavior. Substantial parametric analyses were conducted on typical CFDST column connections to observe the influence of parameters including strength of steel tube, column hollow ratio and bolt pretension force. Furthermore, certain constructional measures commonly employed in engineering practice were also discussed. It was concluded that the CFDST column blind bolted to the steel beam joint has favorable seismic behavior and is feasible for application in high-intensity earthquake regions.

ИМИТАЦИОННАЯ МОДЕЛЬ АВТОМОБИЛЬНОГО МАНИПУЛЯТОРА, РЕАЛИЗОВАННАЯ В СРЕДЕ САПР

The article is devoted to the problems of simulation of the working process of a truck-mounted crane using modern computer-aided design systems and applications for engineering calculations. Currently, analytical methods are mainly used to model the operation of manipulator technology, such as “manual” compilation and solution of Lagrange equations of the second order, or even simpler evaluative calculations based only on basic concepts of theoretical mechanics. However, such objects consist of many parts that are in a complex rotational motion and contact interaction with each other. If such complex systems are modeled by the indicated analytical methods, one has to introduce a number of assumptions that greatly simplify the mathematical model. The level of its adequacy is low. Also recently, numerical methods for modeling mechanisms that are implemented through programming languages by using a detailed description of the process under study are often used abroad. An alternative to these methods is the use of computer-aided design systems in which numerical methods are built-in at the core level of the program and require setting the basic geometric, dynamic and kinematic parameters of the mechanism and the environment, after which they can calculate the functioning parameters of the object under study. The process of creating a simulation model of a truck mounted crane, which is an analogue of an existing laboratory setup, has been considered. To do this, a 3D model of the manipulator in the SolidWorks CAD environment has been developed. The creation technique and the main features of the obtained simulation model have been described

Theory on the looping mediated directional-dependent propulsion of transcription factors along DNA

We show that the looping mediated transcription activation by the combinatorial transcription factors (TFs) can be achieved via directional-dependent propulsion, tethered sliding and tethered binding-sliding-unbinding modes. In the propulsion mode, the first arrived TF at the cis-regulatory motifs (CRMs) further recruits other TFs via protein–protein interactions. Such TFs complex has two different types of DNA binding domains (DBDs) viz. DBD1 which forms tight site-specific complex with CRMs via hydrogen bonding network and the promoter specific DBD2s which form nonspecific interactions around CRMs. When the sum of these specific and cumulative nonspecific interactions is sufficient, then the flanking DNA of CRMs will be bent into a circle over the TFs complex. The number of TFs involved in the combinatorial regulation plays critical role here. When the site-specific interactions and the cumulative nonspecific interactions are strong enough to resist the dissociation, then the sliding of DBD2s well within the Onsager radius associated with the DBD2s-DNA interface towards the promoter is the only possible way to release the elastic stress of the bent DNA. The DBD2s form tight synaptosome complex upon finding the promoter via sliding. When the number of TFs is not enough to bend the DNA in to a circle, then tethered sliding or tethered binding-sliding-unbinding modes are the possibilities. In tethered sliding, the CRMs-TFs complex forms nonspecific contacts with DNA via dynamic loops and then slide along DNA towards promoter without dissociation. In tethered binding-sliding-unbinding, the CRMs-TFs performs several cycles of nonspecific binding-sliding-unbinding before finding the promoter. Elastic and entropic energy barriers associated with the looping of DNA shape up the distribution of distances between CRMs and promoters. The combinatorial regulation of TFs in eukaryotes has evolved to overcome the looping energy barrier.