Uniform Force Distribution Research Articles

Tightening and anti-loosening performance of spring washer connecting bolts

This paper investigates the tightening and anti-loosening performance of phosphated spring washers (i.e., PSW) and galvanized spring washers (i.e., GSW), considering three torques and comparing them with galvanized flat washers (i.e., GFW). Subsequently, a finite element model of the spring washer connecting bolt was established and validated, further investigating the force performance of the spring washer and the stress distribution in the thread area. Finally, a quantitative evaluation method for the anti-loosening performance of spring washers was proposed. The results show that the preload of GSW is maximum after the nut is tightened, and the loss of preload can be supplied by the flattened spring washer. At the same time, the inner ring of the spring washer is sticking, while the outer ring is sliding. Similarly, the contact pressure of the washer decreases radially. During the lateral vibration process, the decrease curve of preload consists of three stages: initial stage, stable stage, and loosening rotation stage. Specifically, GSW has the best anti-loosening performance, because the wear of the zinc layer increases friction. More importantly, the spring washer compensates for the gap between the nut contact surface during transverse vibration, ensuring uniform force distribution in the threaded area and effectively improving the anti-loosening performance.

Effects of stiffeners on anchor rod flexural strength in column base-plate connections

The present paper reports results of a numerical investigation of the mechanical behavior of a column base plate connection subjected to an axial compression force and a bending moment. A three-dimensional nonlinear model was developed, using the Cast3M software, and validated against experimental data. In addition, the material nonlinearity as well as contact conditions between the different components of the connection were thoughtfully considered. Based on the validated model, an extensive parametric analysis was conducted to investigate the effect of stiffeners on the forces in the anchor rods. The results clearly indicate that the design approaches that consider only the tensile strength of anchor rods while neglecting the bending moments can lead to a poor estimation of the forces applied to these rods. They also suggest that adding stiffeners provides additional strength and reduces the anchor rod bending in one direction. However, it is important to note that the stiffeners also induce an additional moment in the opposite direction. This could make the anchor rod more susceptible to biaxial bending with tension. Furthermore, this study proposes a new specific shape of stiffener is suggested (cbp5). It was concluded that the proposed shape of stiffeners allows a more uniform distribution of forces and avoids excessive stress concentrations, effectively prevents the biaxial bending in the anchor rod.

Effects of different loading on the bifurcation of annular elastic rods: Theory vs. experiments

The bifurcation problem of a circular Euler–Bernoulli rod subject to a uniform radial force distribution is investigated under three distinct loading conditions: (i.) hydrostatic pressure, (ii.) centrally-directed, and (iii.) dead load. Previous studies on this apparently ‘familiar’ structural problem have yielded controversial results, necessitating a comprehensive clarification. This study shows that results previously labelled as ‘correct’ or ‘wrong’ simply refer to different external constraints, whose presence becomes necessary only for the two latter loads, (ii.) and (iii.). Moreover, the paper presents the first experimental realization of a circular rod subjected to centrally-directed loads. The experimental findings align with the theoretical predictions and show the exploitation of a new type of load acting on a continuous structural element. The feasibility of this load is demonstrated through the use of inextensible cables and opens the way to applications in flexible robotics when cables are used for actuation.

Automated Grasp Planning and Finger Design Space Search Using Multiple Grasp Quality Measures

As the industry shifts to automated manufacturing and the assembly of parts in smaller batches, there is a clear need for an efficient design of grippers. This paper presents a method for automated grasp planning and finger design for multiple parts using four grasp quality measures that capture the following important requirements for grasping: (i) uniform contact force distribution; (ii) better gravity wrench resistance; (iii) robustness against gripper positioning error; and (iv) ability to resist larger external wrench on the object. We introduce the fingertip score to quantify the grasp performance of a fingertip design over all the objects. The method takes the CAD model of the objects as the input and outputs the optimal grasp location and the best finger design. We use the method for a three-point grasp with a parallel jaw gripper. We validate our method on two sets of objects. Results show how each grasp quality measure behaves on different objects and the variation in the fingertip score with finger design. Finally, we test the effectiveness of the optimal finger design experimentally. The three-point grasp is suitable for grasping objects larger than is possible with shape-matching fingertips.

EXPLORATION OF THE PACKING ELEMENT OF THE ANNULAR BOP

The article delved into exploring various structural configurations of clamping nodes in universal preventers, examining both conical and spherical designs. Anti-discharge equipment is essential for averting well blowouts by sealing well openings and maintaining back pressure during drilling, operation, and testing phases. The reliability and durability of this equipment must undergo rigorous testing to ensure safety. Universal preventers not only manage the wellhead but also facilitate pipeline rotation, vertical movement, and additional pipeline insertion into the well. They effectively seal the wellhead even with identical pipe parts. The sequence of technological processes must be carefully chosen and monitored when selecting preventers to ensure high reliability, longevity, and operational efficiency in oil and gas well activities. One of the critical components in anti-discharge equipment is the clamp knot. Let's delve into the clamp knot of universal preventers. The clamp comprises numerous metal inserts evenly spaced along its length, creating a tight seal at the wellhead by compressing the flexible clamp element. Hydraulic pressure drives a piston to close and open the clamping element. As a result, the clamping element of the universal preventer experiences varying loads in direction and magnitude. A spherical structural design in the clamping element provides better resistance to changing stresses compared to a conical design due to its spherical surface, resulting in uniform force distribution. However, this structural design's drawback is increased wear on the elastic sealing joint due to friction during pipeline movement. Additionally, pressure forces during piston upward movement impact the sealing element's tightness, functionality, and lifespan. Keywords: Anti-discharge equipment, locking element, universal preventer, conical locking device.

Theoretical study of the nonlinear force-loading control in single-molecule stretching experiments

Force spectrum measurements with constant loading rates are widely used in single-molecule manipulation experiments to study the mechanical stability and force response of biomolecules. Force-dependent transition rates can be obtained from the transition force distribution, but it is limited to the force range with non-zero force distribution. Although constant loading rate control can be realized with magnetic tweezers, the loading rate range is limited due to the slow movement of permanent magnets. Non-linear exponential and exponential squared force loading functions are more feasible in magnetic tweezers, while there is no theoretical result available for these two kinds of non-linear force loading functions. In this study, we solved the unfolding process of a protein following Bell’s model under nonlinear exponential and exponential squared force loading functions, which offer a broader range of unfolding force distribution compared to the traditional constant loading rate experiments. Furthermore, we derived two force loading functions, which can produce uniform unfolding force distribution. This research contributes fundamental equations for the analysis of experimental data obtained through single-molecule manipulation under nonlinear force loading controls, paving the way for the use of nonlinear force control in magnetic tweezer experiments.

Experimental evaluation on the mitigation performance of double-layered Kirigami corrugated cladding against impact load

The impact mitigation performance of novel single and double-layered kirigami corrugated (KC) claddings is investigated in this study via drop weight impact tests, as their significant improvements in energy absorption and crushing resistance were previously demonstrated over conventional corrugated structures. The feasibility of mass production on the proposed large-size KC core is also verified by applying conventional multi-stage mould pressing. A total of 15 different configurated single and double-layered KC cladding specimens are prepared and tested, where the effects of impacting speed, impacting mass, layer number, stacking configurations as well as graded design on the impact mitigation performance are considered. Impact force time histories, impact force-displacement curves, and transmitted force time histories at five different locations recorded using a custom-made measuring system are compared to evaluate the impact mitigating performance for the structure placed behind the proposed protective KC claddings. Transmitted force at centre is reduced by more than half as compared with the applied impact force for all double-layered KC claddings. Among the double-layered KC claddings, inverse symmetrically stacked KC cladding with no offset in the bottom layer, as well as the negatively graded KC claddings demonstrate a superior performance with a lower transmitted peak force at the centre and a more uniform force distribution transmitted to the support behind the claddings.

Electrostatic chuck having compliant multi-beam structures with rotatable bipolar pad-shaped electrodes

The demand for the manipulation of flexible film-like objects and those with non-planar surfaces, which cannot be handled using current technologies, has increased considerably. A bipolar electrostatic chuck (ESC) is a device that clamps target objects using a uniform electrostatic force. Traditional ESCs cannot satisfy these demands because of their planar surfaces. Bipolar ESCs with a compliant multi-beam assembly have been proposed to manipulate such objects while leveraging the uniform force distribution of ESCs. Although the proposed compliant ESCs have the potential for such manipulations, increasing the attractive force remains a critical technical issue. This study aims to develop a compliant ESC with pad-shaped bipolar electrodes connected to beam tips with rotational degrees of freedom (RDOFs). Four ESC models with pad-shaped electrodes with different RDOFs between zero and three and one without a pad-shaped electrode are fabricated via 3D printing. The experimental comparison of the five models indicates that an increase in the RDOFs significantly improves the attractive force of each electrode. The high potential of compliant ESCs with three RDOFs at the beam tips is illustrated using three different demonstrations: picking and placing dielectric films, a rigid object with a plane surface, and a rigid object with a curved surface. The results provide insights into the development of industrial electrostatic grippers.

Evaluation of occlusal bite force distribution by T-Scan in orthodontic patients with different occlusal characteristics: a cross sectional-observational study

BackgroundThe aim of orthodontic treatment, apart from esthetic and functional corrections, is uniform force distribution. Hence Occlusal analysis using a T scan gives scope for a precisely targeted treatment plan. The T-scan evaluation of occlusal force, time, and location of contacts from initial occlusal contact to maximum intercuspation enables the orthodontist to sequentially balance the occlusal forces on the right and left sides through specific treatment plan options.ObjectiveThe current study aimed to determine the force distribution in the different individuals by using a T-Scan as well as the net discrepancies of forces generated at a maximum intercuspation position in the first molar region between the left and right sides of the mouth.MethodsThis is a descriptive-correlational study that was carried out in Ras Al Khaimah College of Dental Sciences clinics and Ajman University clinics from January 2020 to September 2022 by using the convenience sampling technique. The T-scan III Novus was employed in this investigation to record multi-bite scans for several patients. T-scan was utilised to examine various malocclusions.ResultsThe present study consisted of 158 participants. Analysis of Variance (ANOVA) showed that there is a statistically significant difference in the percentage of force between the three types of malocclusions (I, II, and III) on the right molar side (B-16 and B-46) (p < 0.05). Moreover, the overall discrepancy showed a statistically significant difference in the three types of malocclusion classifications (p < 0.05). On the other hand, there was no statistically significant difference in the percentage of force between B-26 and B-36 (p > 0.05). Post hoc analysis showed a statistically significant difference in the percentage of force between malocclusion classes I and III on the right molar, with a mean difference of 4.11190 (p < 0.05). Similarly, there was a statistically significant difference in B-46 between Malocclusion Classes I and II, 4.01806 (p < 0.05). Additionally, post hoc analysis showed a statistically significant difference between malocclusion classes I and III, with a mean difference of -4.79841 (p < 0.05) on the right molar.ConclusionThe T-Scan is a useful tool for assessing occlusal discrepancies and can be helpful during treatment planning and follow-up, especially for orthognathic surgery patients. A T-scan could be used in orthodontic therapy in a simple and efficient way. Also, it turned out to be a useful tool for diagnosing problems and gave us new information about how therapies work. In this study, T-Scan showed that it can measure occlusal forces in timing in an objective, accurate, and repeated manner. The current study found that T-Scan was better able to report the difference in the percentage of force on the right molar side than on the left side.

Robotic Cardiac Compression Device Using Artificial Muscle Filaments for the Treatment of Heart Failure

Heart failure occurs when the heart cannot pump adequate blood to the body, which afflicts over 60 million people worldwide. Its treatment options include physiotherapy, medication, mechanical heart support, heart surgery, or heart transplantation. Ventricular assist devices have direct blood contact while passive ventricular constraint devices have only modest therapeutic efficacy. Current direct cardiac compression devices are either bulky, require noisy driving pneumatic sources, or are unable to mimic the natural heart motion. This study introduces a robotic cardiac compression device made of soft artificial muscle filaments that can simultaneously produce radial, axial, and torsional movements, potentially augmenting the pumping function of a failing heart. An empirical model is developed to describe the device motion and an artificial pericardium is employed to enable uniform force distribution to the heart and real‐time pressure sensing. The proposed device could deliver a stroke volume of 70 mL at 15 beats per minute, or a cardiac output of 1.05 L min−1, and achieve a peak instantaneous flow rate of 2.8 L min−1 and an output pressure of 50 mmHg. The new devices are highly customizable and experimentally validated with fresh porcine heart. They are expected to inspire future development of nonblood‐contacting cardiac assist devices.

In-plane, out-of-plane, and in-plane/out-of-plane interactional behavior of masonry-infilled steel MRFs with different frame components flexibilities and considering openings

In this paper, the in-plane (IP), out-of-plane (OOP), and IP/OOP interactional behavior of masonry-infilled steel moment-resisting frames (MRFs) are investigated through calibrated finite element modeling and analyses. Some of the key parameters influencing the response of masonry-infilled frames (MIFs), namely panel aspect ratio, size of central window opening, and steel frame components flexibility, are studied in a parametric study, covering a wide range of values for the parameters. The effect of each considered parameter on the IP and OOP response of MIFs are investigated. In addition, the suitability of various existing equations for predicting the IP and OOP strength of infills are evaluated, and based on the results obtained in this study, new formulae capable of predicting MIFs response characteristics are proposed. A novel non-uniform OOP force distribution pattern based on the first mode shape of free vibration of infilled frames is introduced and implemented, and OOP strength capacity of considered MIFs under this new force pattern are compared with those obtained from common uniform OOP force distribution method. For the IP/OOP interaction analyses, a novel loading protocol is introduced and adopted, and its suitability is compared with that of the common loading protocols used in the literature and discussed in detail. Finally, capacity of masonry infill walls subjected to simultaneous IP and OOP loadings were derived and, based on the results, a new interaction curve formulation was proposed. The results signified that the interaction curve formulation prescribed by ASCE/SEI 41-17 Standard is unconservative.

An Improved Finite Element Model to Study Stress Concentration Around an Elliptical Cutout in Pressure Vessel : Application- Part II

The application of finite element method (FEM) to the solution of cutout and inclusion problems in Filament Wound Fibre Reinforced Plastic (FWFRP) pressure vessel is considered. The analysis of pressurised laminated composite shell, which can be regarded as a heterogeneous body consisting of a finite number of orthotropic layers bonded together, with an elliptical hole is carried out. The influence of uniform shear force distribution along the hole boundary is studied. The numerical results of pressurised laminated composite shell with transverse elliptical hole filled by edge bonded elastic cover are also presented. Predicted stress distribution through the thickness of composite shell with cutout/inclusion at critical locations on the hole boundary is presented in graphical form and discussed.

Optimization of Fixture Layout and Clamping Force in a Concurrent Environment to Improve the Part Quality in Milling Operations

Fixture layout design (FLD) determines the specific position of locators and clamps to position and support the workpiece with respect to a machine tool. The FLD approaches that use Finite Element Analysis (FEA) are widely used in previous works, and it becomes computationally expensive and specific to a particular problem. Further, the FLD and clamping force optimization were often performed separately, ignoring their interdependence. In the present work, to maximize the dimensional and form quality of the part, the reaction forces of the locators are made uniformly distributed by suitably varying the fixture layout and clamping force. The parametric rigid body model is used to depict the behaviour of the workpiece-fixture system, and it is incorporated with the genetic algorithm to optimize the design variables. A prismatic workpiece with slot milling operation is considered to validate the proposed methodology. Stability criterion and tool-fixture interference are considered constraints. Subsequently, FEA is used to verify the integrity of the proposed approach. The results infer that the uniformity in distribution of maximum elastic deformation of the workpiece is achieved due to the uniform distribution of reaction forces. Further, the effects of cutting forces on fixture layout and clamping forces are studied.

Numerical study on the effects of stud degradation and stud arrangement on the fatigue performance of steel-UHPC composite decks

The fatigue degradation of stud connectors is generally neglected in the fatigue analysis of steel-UHPC composite decks, which may lead to inaccurate results. This paper studies the effects of stud degradation and stud arrangement on the fatigue behavior of steel-UHPC composite decks via finite element analysis. A numerical method for the fatigue analysis of composite decks is proposed considering the fatigue degradation of studs. The numerical method is experimentally validated and applied to evaluate the fatigue performance of composite decks. The effect of stud arrangement on the fatigue response of composite decks is studied by parametric analysis. The results indicated the fatigue degradation of studs and the decrease in stud spacing caused more uniform distribution of shear forces at steel-UHPC interfaces. The fatigue degradation of stud connectors reduced the structural stiffness, while reducing the stud spacing enhanced the local stiffness but increased the stress ranges of some fatigue-critical details. Neglecting the stud degradation could lead to an underestimation of the fatigue life of stud connectors. This study advances the understanding of the fatigue behavior and the ability to analyze the fatigue behavior of steel-UHPC composite decks.

Numerical improvement to Glauert correction for the flow around a wind turbine

AbstractAccurate and reliable computation of the aerodynamic characteristics of wind turbines is very important for the development of new efficient designs. The flow around a wind turbine is modeled by a permeable disc (PD), solved through the Unsteady Reynolds-Averaged Navier–Stokes equations (URANS), here named PD/URANS method. The finite volume method and a total variation diminishing (TVD) scheme solve numerically the flow governing equations. The turbulent flow in the wake of the wind turbine is simulated utilising a one-equation turbulence model. The Glauert correction calculation considers a uniform normal force distribution (CT) on the virtual permeable disc applied to the flow, while the axial induction factor is obtained directly from the numerical solution of the URANS equations. The numerical axial induction factor obtained agrees fairly well with Glauert correction, except if the flow behind the turbine is highly unsteady and Reynolds number dependent.

Acellular Dermal Matrix Cover Improves Skin Growth during Tissue Expansion by Affecting Distribution of Mechanical Forces.

Biological cover over tissue expander prostheses has been introduced to provide soft-tissue support for tissue expanders during breast reconstruction. However, its impact on mechanically induced skin growth remains unknown. This study investigates the hypothesis that covering the tissue expander with acellular dermal matrix (ADM) affects mechanotransduction without compromising the efficacy of tissue expansion. Tissue expansion, with and without use of ADM, was performed on a porcine model. The tissue expanders were inflated twice with 45 mL of saline, and the full-thickness skin biopsy specimens were harvested from expanded and control unexpanded skin 1 week and 8 weeks after the final inflation. Histologic evaluation, immunohistochemistry staining, and gene expression analysis were performed. Skin growth and total deformation were evaluated using isogeometric analysis. The authors' results demonstrate that use of ADM as a biological cover during tissue expansion does not impede mechanotransduction that leads to skin growth and blood vessel formation. Isogeometric analysis revealed similar total deformation and growth of expanded skin with and without a biological cover, confirming that its use does not inhibit mechanically induced skin growth. In addition, the authors found that use of an ADM cover results in more uniform distribution of mechanical forces applied by the tissue expander. These results suggest that ADM improves mechanically induced skin growth during tissue expansion by facilitating a more uniform distribution of mechanical forces applied by the tissue expander. Therefore, the use of a biological cover has potential to improve outcomes in tissue expansion-based reconstruction.

Consciousness, Perspective, and Implementation of Selective Grinding in Complete Dentures among Prosthodontic Postgraduates in India

Background and Objectives: Success of prosthodontic treatment in edentulous patients depends on acceptable function and esthetics of complete dentures. Complete denture occlusion plays a role in providing uniform distribution of masticatory forces, better retention, and stabilization of denture bases. In our study, the consciousness, perspective, and implementation of selective grinding in prosthodontic postgraduates (PGs) in India were assessed. Materials and Methods: A pretested, self-administered, and closed-ended questionnaire comprising different sections formed the survey instrument. A structured questionnaire containing 14 questions was framed. A specially created web-designed survey in Google Forms was circulated among prosthodontic PG students and the responses were recorded. Results: The questionnaire consisted of 11 nondemographic questions. About 67.5% of the responses were correct. The outcome of the study can be considered fair. Conclusion: A good occlusal philosophy combined with esthetics is paramount in the patient acceptance of a complete denture prosthesis. Its knowledge and implementation are paramount toward the success of treatment.

Comparison of flexible and rigid annuloplasty rings in isolated mitral regurgitation

Objectives: The aim of this study was to examine the early and midterm results of various annuloplasty rings in terms of residual mitral regurgitation (MR) in patients undergoing mitral valve repair. Patients and methods: In the retrospective study, 298 patients (157 males, 141 females; mean age: 58.8±14.3 years; range, 16 to 82 years) underwent repair between September 2009 and April 2012. Two hundred eleven were assigned to the flexible ring group (Group 1), whereas 87 were included in the rigid ring group (Group 2). Mitral pathologies were divided into three subgroups: ischemic, degenerative, and rheumatic. Results: The causes of mitral pathology were ischemic in 36.2%, degenerative in 54.4%, and rheumatic in 9.4%. Concomitant surgical procedures were present in 87%. The follow-up period ranged from 2 days to 33 months, with a mean of 15.8±7.5 months. The 30-day mortality rate was 9.2% and 10.4% in Groups 1 and 2, respectively. There was a high rate of successful repair in the rigid group with 88.5% and acceptable rate of repair in the flexible group with 72%. Mitral regurgitation was significantly reduced after intervention regardless of the ring type (p&lt;0.01). Significant improvement in NYHA class was observed in both groups. Recurrent regurgitation was detected in 27.9% of patients in Group 1 and 11.5% in Group 2. Recurrence occurred within three to nine months following the surgery. Reoperation rates for residual MR were 3.3% (n=7) vs. 1.1% (n=1) in Groups 1 and 2, respectively (p=0.293). Conclusion: Saddle-shaped rings provide a mechanical benefit through a low and uniform force distribution and improve repair durability compared to flat rings. As a result, the rigid ring had a significant advantage, particularly in degenerative and rheumatic subgroups, but there was a loss of superiority in late ischemic MR due to left ventricle remodeling.

Splice Connections for Built-Up Column Assemblies in Cold-Formed Steel Construction

The development of simple connection methods is necessary for increasing cold-formed steel (CFS) construction activities. A new splice connection concept for the CFS built-up column-to-column connections is presented in this paper. This simple connection concept will use the same size and shape of the geometry as the CFS built-up column, which will enable a quick erection process. The new splice connection configurations, arrangement, and installation methods for cold-formed steel construction are demonstrated. Twenty-eight experiments, which include four actual columns, two disconnected columns, and 22 columns with splice connections, are carried out. This paper examines the influence of various parameters of splice connections such as length, thickness, and number of fastener rows. The design strength of the actual column is determined using the direct strength method (with modified global and local slenderness approaches) and is compared with the results of the splice connected columns for adequacy. The force transfer mechanism and failure modes of splice connection components are demonstrated in the form of detailed sketches. The smaller length splice connections led to localized failures, while the longer splice connections enabled the uniform force distribution between the built-up column cross-sections. Finally, it is recommended that the splice connection configuration should be a minimum of 300 mm in length, the splice thickness should be equal to the CFS built-up cross-section, and two rows of fasteners for attaining the required design strength of the built-up column members.

An integrated approach for Fixture Layout design and Clamping Force Optimization

Fixture Layout Design (FLD) determines the specific position of locators and clamps to orient and holds the workpiece with respect to a machine tool. The FLD approaches that use Finite Element Analysis (FEA) have been widely used in previous works and have become computationally expensive and specific to a particular problem. Further, the FLD and clamping force optimization were often performed separately by ignoring their interdependence. In the present work, the locators' contact forces are uniformly distributed by suitably varying the fixture layout and clamping force to maximize the part dimensional and form quality. The parametric rigid body model is used to depict the behaviour of the workpiece-fixture system, and it is incorporated with the genetic algorithm to optimize the design variables. A prismatic workpiece with pocket milling operation is considered to validate the proposed methodology. Stability criterion and tool-fixture interference are considered constraints. Subsequently, FEA is used to verify the integrity of the proposed approach. The results infer that the uniform distribution of maximum elastic deformation is achieved due to the uniform distribution of contact forces. The suggested approach is proven effective for designing a milling fixture to manufacture components with high dimensional and form precision.