Fastener Joint Research Articles

Analytical Assessment of Composite L Angle Strength Under Internal Fuel Pressure in Composite Wing

The Interspar (IS) box stores the turbine fuel in the composite wing of an Aircraft. The filled fuel is under pressure that induces out-of-plane stresses on all the wing’s structural members around the fuel tank’s boundary. The wing is designed using carbon fiber reinforced plastic (CFRP) with the co-curing of the bottom skin and its stringers along with front and rear spars. A suitable number of cut-outs are made on the top and bottom sides of the IS ribs for the stringer to pass through them. The global finite element analysis showed that the stringer cut-out regions in the IS ribs are highly stressed, as they are subjected to out-of-plane load due to internal fuel pressure, which induces transverse tensile stress in the cut-out region. Resin is the weakest material in the composite laminate, but it has to resist the high-stress component due to out-of-plane loads. The top and bottom flanges of the ‘C’ section IS ribs geometrically form an L angle section with a stringer cut-out made in it. At the L angle location, the IS ribs are critical from both the strength and stiffness point of view. Strength and stiffness at the interface of the fastener joint are essential factors in maintaining the composite wing’s overall structural integrity under internal fuel pressure. The authors adopted the same standalone finite element (FE) modelling approach developed for the Bond Energy Method and carried out appropriate analytical studies to ascertain the safety and structural integrity of the composite wing under internal fuel pressure. This article presents the analytical study carried out on the standalone FE model of an L angle with the stringer cut-out introduced at its appropriate position. The static stress analysis is carried out by enforcing the global displacement on this standalone FE model and extracting three force components in CBAR beam elements representing the resin property in the transverse direction of the composite laminate. The stresses are calculated outside the analysis deck using Excel® spreadsheets. The maximum Normal Stress (σn) in the L angle flange is found to be 13.25 MPa, which is well within the resin or transverse tensile strength of the composite laminate 53 MPa, and the shear stress is found to be 11.10 MPa, which is less than the resin shear strength property of 23 MPa. Hence the study showed that the L angle is safe for carrying internal fuel pressure of 12.5 PSI. The study also showed that the strain and displacement values distribution in the standalone FE model are comparable with that of the global wing box model within the range of (8-10) % and (4-5) % difference, respectively.

Influence of Guardrails on Track–Bridge Interaction with a Longitudinal Resistance Test of the Fastener

The guardrail is an indispensable part of ballasted track structures on bridges. In order to reveal its influence on the track–bridge interaction of continuous welded rail (CWR), the longitudinal resistance model of the guardrail fastener and its influential factors are established through tests. By taking a continuous girder bridge (CGB) for railways as an example, a stock rail-guardrail-sleeper-bridge-pier integrated simulation model is developed. The effects of the guardrails, installation torque of the guardrail fastener, and joint resistance of the guardrail under typical conditions are carefully examined. The research results indicate that the nominal longitudinal resistance of the guardrail fastener and the elastic longitudinal displacement of the rail prior to sliding approximately grow linearly with the growth of the installation torque. The presence of a guardrail can alleviate the track–bridge interaction in the range of the CGB, but exacerbate the interaction near the abutment with moveable bearings. This fact enables the abutment position to be considered as a new control point for the design of CWR on bridges. Considering the changing rules of the rail longitudinal force and rail gap, it is recommended that the installation torques of the guardrail fastener and guardrail joint are 40–60 N·m and 700–800 N·m, respectively. The recommended maximum longitudinal stiffness of piers for CGBs is evaluated. When the longitudinal stiffness of the pier for a CGB is lower than the recommended value, the influence of the guardrail can be neglected in the design of the CWR.

Changes in friction of zinc flake coated threaded fasteners due to humidity, temperature and storage duration

The friction coefficient of a specific material combination is often assumed to be invariant in manufacturing processes such as during the tightening of threaded fastener joints. This paper considers the impact of storage conditions on threaded fastener friction. Fasteners were stored in hot humid and sub-zero temperature conditions to study friction in the thread and under-head contacts. Four Zn-flake coatings, commonly used in the automotive industry were considered. Consequent tightening of these fasteners at room temperature revealed that storage history had a significant impact on their friction coefficients, halving under-head friction in some cases. This varied behavior was considered to be a response to coating nano-hardness and structure and differences in adsorption/absorption of water and zinc-oxide formation during storage.

Railway defect detection based on track geometry using supervised and unsupervised machine learning

Track quality affects passenger comfort and safety. To maintain the quality of the track, track geometry and track component defects are inspected routinely. Track geometry is inspected using a track geometry car (TGC). Measured values are stored in the machine and processed to evaluate the track quality. However, track component defects require more effort to inspect. Track component defects can be inspected manually which is time- and workload-consuming or using sensors installed at additional cost. This study presents an approach using track geometry obtained by a TGC to detect track component defects, namely, rail, switch and crossing, fastener and rail joint defects. Detection models are developed using several supervised machine learnings. The relationships between track component defects are analysed to gain insights using unsupervised machine learnings. From the study, the best model for detecting track component defects using track geometry is a deep neural network with an accuracy of 94.31% followed by a convolutional neural network with an accuracy of 93.77%. For the exploration of insights, k-means clustering is used to cluster the track components defects, and association rules are used to find the relationships between them. Examples of the insights from applying these two techniques are that switch and crossing defects are usually found where the radius of curvature is less than 2000 m and the gradient is positive, the most common defects when the radius of curvature higher than 4000 m are rail defects, or a worn wing rail will be found when the rail section has failed, ties in switches and worn point blades are found with the confidence of 92.17%. The findings of the study can be applied to detect track component defects using track geometry where additional cost is not required and unsupervised machine learning provides the insights that will be beneficial for railway maintenance. The information obtained from machine learning models will be complementary information to support decision making and improve the maintenance efficiency in the railway industry.

A Two-Dimensional Model for Pin-Load Distribution and Failure Analysis of Composite Bolted Joints.

Multibolt composite joints are widely used in aircraft structures. The determination of the pin-load distribution among the bolts is a critical step in the failure prediction of bolted joints. In this paper, a two-dimensional model of the multibolt composite structure is established for the pin-load distribution analysis. Its accuracy is validated by experimental results and the results from a 3D finite element model. Based on the determined pin-load distribution, FE models for a laminated plate with three-row fastener joints are built for failure prediction. Hashin stress criteria and the degradation guidelines of the material stiffness with respect to the different failure modes proposed by Tserpes are applied for the failure evaluation and the material degradation, respectively. The failure location and ultimate load are well predicted, which further validates the effectiveness and applicability of the proposed model for the pin-load distribution analysis.

ЧИСЛЕННОЕ ИССЛЕДОВАНИЕ РАБОТЫ ЗАМКОВОГО СОЕДИНЕНИЯ СТЕНОВЫХ ПАНЕЛЕЙ НА РАСТЯЖЕНИЕ ДО ОБРАЗОВАНИЯ ТРЕЩИН

A large-panel design scheme includes floor elements, wall panel elements, and joints between them. The rigidity and strength characteristics in tension, compression and shearare required to be knownfor correct modeling of large-panel buildings. Due to the lack of universal formulas in the normative and reference literature for determining the strength and rigidity of various types of joints, it is necessary to conduct additional research. In 2014 a new type of vertical monolithic joint for large-panel buildings was developed: the fastener joint of wall panels, which has significant strength and rigidity. The fastener includes acheck clamp, which connects the loop outlets on panel ends and the steel plate, which connects the ends of the clamp. It isnecessary to correctly evaluate the strength and rigidity of the joint for its fully- functional application. The experimental research on the joint in tension discovered its bilinear force-deformation relationship (with great rigidity before cracking, and with marginal one after). To analyze the large-panel buildings under the influence of the main operational loads, it is enough to model the joint’s work on the first stage (before cracking). The aim of the research is to study the fastener joint in tension before cracking. The paper compares the results of numerical modeling with the sample testing results, and determines the rigidity and cracking load for joints with other values of the grouting concrete strength and the diameters of the loop outlets. The research was carried out using flat finite-element model in the Lira-SAPR CAD software package. The results of calculation of the joint model are generally consistent with the results of samples testing. In addition, the rigidity and cracking load were determined for joints with various parameters (concrete strength and loop outlet diameter). The results of the study can be usedfor designing large-panel buildings with this type of joint.

A study on prognostic analysis of attachment lugs under off-axis loading

PurposeLug joints with fasteners play a crucial role in connecting many major components of the aircraft. Most of the failures in the past were credited to the damages initiating and progressing from these types of joints. Ensuring the structural integrity of these fastener joints is a major issue in many engineering structures, especially in aerospace components, which would otherwise lead to fatal failure. The purpose of this paper is to adopting the prognostic approach for analysing these lug joints with fasteners subjected to off-axis loading by estimating the crack initiation and crack growth life of these joints. This data will be useful to estimate the remaining life of these joints at any given stage of operations, which is mandatory in structural health monitoring (SHM).Design/methodology/approachStraight and tapered lug joints are modelled using the finite element method in MSC PATRAN and analysed in MSC NASTRAN. These lug joints are analysed with a push fit fastener. The contact/separation regions at the pin–lug interface are carefully monitored throughout the analysis for various loading conditions. Critical locations in these lug joints are identified through stress analysis. Fatigue crack initiation and fatigue crack growth analysed is carried out at these locations for different load ratios. A computational method is proposed to estimate the cycles to reach crack initiation and cycles at which the crack in the lug joint become critical by integrating several known techniques.FindingsAnalysis carried out in this paper describes the importance of tapered lug joints, particularly when subjected to non-conventional way of loading, i.e. off-axis loading. There is a partial loss of contact between pin and lug upon pin loading, and this does not change further with monotonically increasing pin load. But during load reversals, there is a change in contact/separation regions which is effectively handled by inequality constraints in the boundary conditions. Crack growth in these lug joints pertains to mixed-mode cracking and is computed through the MVCCI technique.Originality/valueMost of the earlier works were carried out on in-plane pin loading along the axis of symmetry of the lug. The current work considers the off-axis pin loading by loading the lug joints with transverse and oblique pin load. The significance of taper angle under such loading condition is brought in this paper. The results obtained in this paper through prognostic approach are of direct relevance to the SHM and damage tolerance design approach where the safety of the structural components is of foremost priority.

Behavior of glued laminated bamboo and bamboo-oriented strand board sheathing-to-framing connections

In order to extend the application of bamboo-based products in the field of construction, this study reports on a preliminary experimental evaluation of the behavior of sheathing-to-framing connections comprised of bamboo oriented strand board (BOSB) and glued laminated bamboo (GLB) and the applicability of the load–displacement model to the GLB–BOSB connections. Different dowel types and edge distances were considered in monotonic tests. In order to conduct a direct comparison of the behavior of the BOSB connection to plywood and oriented strand board (OSB) sheathing in shear walls, three panels for sheathing were subjected to monotonic and cyclic tests. The results indicated that different types of dowel affected significantly the lateral resistance performance of GLB–BOSB connections. The hex head self-tapping screw joint had stiffer and stronger lateral resistance performance but lower deforming ability. In addition, the edge distances of fastener joints significantly influenced the lateral load carrying capacity. The results of monotonic and cyclic tests of the three sheathing panel connections indicated that BOSB panels showed a pattern of superior lateral load capacity, and the energy dissipation by BOSB joints was greater than that of OSB and plywood connections with the same framing prior to the damage. Furthermore, the exponential prediction equation modeled the shape of experimental curves with reasonable accuracy that was applicable to GLB–BOSB connections.

Topology optimization of joint load control with geometrical nonlinearity

This paper presents an extended topology optimization approach considering joint load constraints with geo-metrical nonlinearity in design of assembled structures. The geometrical nonlinearity is firstly included to reflect the structural response and the joint load distribution under large deformation. To avoid a failure of fastener joints, topology optimization is then carried out to minimize the structural end compliance in the equilibrium state while controlling joint loads intensities over fasteners. During nonlinear analysis and optimization, a novel implementation of adjoint vector sensitivity analysis along with super element condensation is introduced to address numerical instability issues. The degrees of freedom of weak regions are condensed so that their influences are excluded from the iterative Newton-Raphson (NR) solution. Numerical examples are presented to validate the efficiency and robustness of the proposed method. The effects of joint load constraints and geometrical nonlinearity are highlighted by comparing numerical optimization results.

Fatigue Life Benefits of Cold Worked Holes in Fastener Joints

Lug joints with fasteners play a vital role in connecting major components of flight vehicles by acting as primary load carrying members. The structural integrity of these fastener joints and in particular fatigue life is of prime concern from the design point of view. Cold working of holes is one of the methods of achieving enhancement of fatigue life of these joints and this aspect is computationally addressed in this paper. The process of cold working is modeled, consists of introduction of a large diameter mandrill into the hole and withdrawing it leaving behind plastically stretched material around the hole periphery. Later one can use this hole with interference or clearance fit pins for better fatigue life. Material non-linear analysis is employed during the cold working process. These issues are addressed in this paper through computational approach using FEM software MSC NASTRAN/PATRAN. The fatigue life is computed at the identified critical locations through stress analysis using modified Basquin’s equation with Morrow’s mean stress effect. Life of the lug joints before and after cold working of the hole are estimated and compared.

Optimal Selection for Dissimilar Materials using Adhesive Bonding and Mechanical Joining

In the present study, an investigation of double lap joints using two different joining methods was carried out. Carbon fiber and glass fiber reinforced materials were the composite materials that joined with the conventional steel and aluminium. Adhesive bonding joint and a combination of adhesive and mechanical fastener joints were used as a joining approach. It is found that adhesive bonding joint provided a better performance compared to the hybrid joint, where the holes created in the specimens for inserting mechanical fasteners caused a lower strength. It is observed that the adhesive joining of the glass fiber and steel obtained a maximum load of 35.5 KN, which is the highest strength among all other combinations examined in this study, while the similar combination joined using adhesive bonding and mechanical fastener showed a maximum load less than the adhesive joining by 21.4 %.

Ouput Property of Smart Bolt and Loosening Sensing of Adjoining Bolt in In-line Array Shear Fastener Joint

Ouput Property of Smart Bolt and Loosening Sensing of Adjoining Bolt in In-line Array Shear Fastener Joint

Experimental Study on Bearing Capacity of Reinforced Steel Tubular Scaffold under Uniform Loads

Five groups of tests were designed to analyze the influence of node types (fastener connection and mortise‐and‐tenon joint) and reinforcement modes of top horizontal cross rods (weak truss and stiffening truss) on the bearing capacity of the steel tubular scaffold under vertical uniform loads. Loading phenomenon, bearing capacity, failure mode, displacement at key positions, and strain development characteristics during tests were analyzed. The following conclusions were drawn: (1) The fastener scaffold reinforced by a top truss showed the highest bearing capacity and high material utilization. (2) The fastener scaffold reinforced by a top weak truss increased the bearing capacity and caused coordinated deformation of the top horizontal force rods. (3) The node displacement of the mortise‐and‐tenon scaffold was smaller than that of the fastener joint, whereas its bearing capacity was higher. (4) Vertical diagonal bracing can slightly increase the bearing capacity of the mortise‐and‐tenon scaffold but can also constrain the deformation of the vertical rods and change the failure mode.

Fracture Behavior of Fastener Joints of CFRP Laminates Subjected to Bearing Force and Bypass Force

Fracture Behavior of Fastener Joints of CFRP Laminates Subjected to Bearing Force and Bypass Force

Experimental and analytical study of an CF-PEEK Fastener all composites single-lap shear joint under static and fatigue loading

This paper presents a detailed experimental study on carbon fibre (CF) polyether etherketone (PEEK) composite fasteners designed to join conventional high performance composites (CFRP). The failure mechanisms of two CF-PEEK fasteners with countersunk heads joining two laminate plates in a single-lap configuration were investigated under static (tensile) and cyclic loading (tension–tension). The failure process of the bolted joints is described in detail using acoustic emission and microscopic cut views. For comparison the CF-PEEK fasteners were replaced by metal fasteners (Titanium) under the corresponding conditions and loadings. The experimental results are in good agreement with the newly developed “closed-form” model up to the damage point of the joints. This enhanced analytical approach is a closed-form extension of the spring-based method, where bolts and laminates are represented by an arrangement of springs and masses. The model covers in all variables influencing the joint behaviour, such as fastener position, joint material, fastener type, hole diameter, joint thickness, bolt-hole clearance, and bolt torque.

Research on Pin-load Distribution for Countersunk Joint Considering Accumulated Damage of Composite Laminates

The paper presents a numerical simulation about the damage process of the multiple countersunk bolted double-lap joints based on the cumulative damage theory which is widely used to estimate the mechanical strength of fastener joints, the Hashin’s failure criterion, and the Tan’s stiffness degradation model, and investigates the influence of the composite materials cumulative damage on the pin-load distribution. The numerical model of composite joints has been established in the commercial finite element software ANSYS to research the influence of the composite cumulative damage on the pin-load distribution, to assess the feasibility of integral analysis as well as to evaluate the error and rationality of traditional methods by applying the global analysis technology. The conclusions demonstrate that the results obtained with the method of composite cumulative damage considering properties degradation are close to those of conventional methods. The pin-load distribution is characterized by “Bolts at both ends bearing greater load, the central bolts bearing smaller load” during the whole loading process. Using conventional methods to study the pin-load distribution is easy and efficient to meet the needs of engineering application.

CTH shock physics simulation of non-linear material effects within an aerospace CFRP fastener assembly due to direct lightning attachment

This study examines detailed CTH simulation results of a carbon fiber composite panel assembly where the binding titanium fastener joint is the attachment point of a direct lightning strike. A refined COMSOL Multiphysics electromagnetics calculation is performed on the undeformed installed fastener geometry to obtain current and electric field solutions in time using SAE ARP5412B lightning test waveforms. Electro-mechanical coupling is achieved through the use of Joule heating resulting from J·E, the power per unit volume dispersed throughout the structure due to the lightning energy transport. The shock physics code CTH is used to model the fluid-structure calculations which involve highly non-linear and high temperature effects. Experimental data, in the form of material effects images, are used for validation of material and equation of state selections. Discussion of the effects created by the lightning energy depositions focuses primarily on gas conditions in the inner spaces surrounding the fastener and the associated local geometrical changes. The spatiotemporal pressure evolution within the fastener assembly cavities are compared with experimental results and the importance of modeling chemistry changes in future work are discussed within the conclusion.

Detection of Bolt Loosing in Shear Fastener Joint of In-line Array by Smart Bolt

Detection of Bolt Loosing in Shear Fastener Joint of In-line Array by Smart Bolt

A hysteresis model for timber joints with dowel-type fasteners

Predicting the mechanical behaviour and the failure mechanism of timber joints with dowel-type fasteners requires consideration of several factors, including the geometrical and mechanical properties of the metal fastener, the physical properties of timber and the interaction between such elements. This paper proposes a numerical model where a joint is schematized as an elasto-plastic beam in a non-linear medium with a compression-only behaviour. Unlike the differential approach adopted by most of the hysteresis models published in literature, this model predicts the load-displacement response using simple mechanical relationships and basic input parameters. Furthermore, the model is capable of reproducing the effect of the cavity formed around the fastener by timber crushing, and simulates the hysteretic behaviour and the energy dissipation under cyclic conditions. Shear tests are reproduced on nailed steel-to-timber joints in Cross-Laminated Timber and results are compared to the experimental test data obtained on similar single fastener joints. Simulations lead to accurate predictions of both the mechanical behaviour (initial stiffness, maximum load-carrying capacity, global shape of the loading curve and of the hysteresis cycles) and the total energy dissipation observed in the tests.

Experimental and Numerical Research on Tensile Performance of Inter-Panel Fastener Joints of Large-Panel Buildings

When designing large-panel buildings, it is necessary to take into account the work of wall panel joints. In addition to welded joints, monolithic joints in the form of pinned joints of the loop releases of adjacent wall panels are widely used. The main characteristics of a joint in the design scheme are its rigidity and bearing capacity under the action of shear and tensile (compressive) forces. This paper studies a new type of an inter-panel joint in the form of a fastener junction of wall panels made using a bracket of reinforcing steel and a metal plate joining the ends of the bracket. Due to the creation of a closed loop of voltages in the node, its high load-bearing capacity is assumed as well as the possibility of using this connection under dynamic effects on the building. An experimental study of the strength and rigidity of the joint at tensile loading along the joint axis was carried out, the breakdown of the joint, the stiffness characteristics and the bearing capacity of the samples were determined. The numerical modeling of the joint’s work on stretching to the formation of cracks is carried out.