Dovetail Joints Research Articles

Mechanical behaviour of a novel steel dovetail joint subjected to axial compression loading

In this study, two types of novel steel dovetail joints for single-layer grid shells are proposed and investigated. The design concept, design method, and FE modelling method are discussed. Experimental and numerical analysis methods are adopted to explore the performance of the new joint system under axial compression loads. Moreover, a parametric analysis is conducted to evaluate the impact of design parameters including the hub diameter, hub ring thickness, hub height, hub slot edge thickness, and beam-throat slope angle on the joint behaviour. Based on the experimental and numerical results, both types of joints exhibit the same performance under compression loading, with three main failure modes: beam-throat failure, hub failure, and combined beam-throat and hub failure. Beam-throat failure occurs when the compressive bearing capacity of the hub is greater than that of the beam neck. The hub failure mode occurs when the compressive bearing capacity of the beam is higher than that of the hub, and the combined failure mode occurs when the compressive bearing capacities of the hub and beam-throat are similar. Finally, equations for calculating the yield and ultimate bearing capacities of the examined joints and hubs are proposed and calculated. By comparing the numerical, theoretical, and corresponding experimental results, it is shown that the derived equations can be used to calculate the mechanical performance of the joints in this study.

Computation of damped nonlinear normal modes for large scale nonlinear systems in a self-adaptive modal subspace

The concept of nonlinear modes has been proved useful to interpret a wide class of nonlinear phenomena in mechanical systems such as energy dependent vibrations and internal resonance. Although this concept was successfully applied to some small scale structures, the computational cost for large-scale nonlinear models remains an important issue that prevents the wider spread of this nonlinear analysis tool in industry. To address this challenge, in this paper, we describe an advanced adaptive reduced order modelling (ROM) technique to compute the damped nonlinear modes for a large scale nonlinear system with frictional interfaces. The principle of this new ROM technique is that it enables the nonlinear modes to be computed in a reduced self-adaptive modal subspace while maintaining similar accuracy to classical reduction techniques. The size of such self-adaptive subspace is only proportional to the number of active slipping nodes in friction interfaces leading to a significant reduction of computing time especially when the friction interface is in a micro-slip motion. The procedure of implementing this adaptive ROM into the computation of steady state damped nonlinear mode is presented. The case of an industrial-scale fan blade system with dovetail joints in aero-engines is studied. Damped nonlinear normal modes based on the concept of extended periodic motion is successfully calculated using the proposed adaptive ROM technique. A comparison between adaptive ROM with the classical Craig-Bampton method highlights the capability of the adaptive ROM to accurately capture the resonant frequency and modal damping ratio while achieving a speedup up to 120. The obtained nonlinear modes from adaptive ROM are also validated by comparing its synthesized forced response against the directly computed ones using Craig-Bampton (CB) method. The study further shows the reconstructed forced frequency response from damped nonlinear modes are able to accurately capture reference forced response over a wide range of excitation levels with the maximum error less than 1% at nearly zero computational cost.

Numerical and Theoretical Study on Mechanical Behaviors of New Dovetail Joint System (NDJs) Subjected to Tensile, Compressive, and Out-of-plane Bending Moment Forces

Numerical and Theoretical Study on Mechanical Behaviors of New Dovetail Joint System (NDJs) Subjected to Tensile, Compressive, and Out-of-plane Bending Moment Forces

A Dovetail Joint for a Segment Permanent Magnet on a Rotor

Specific weight-power parameters (kW/kg, (kW/dm3)) of rotary electric machines depend on the rotational speed of the rotor. Bandage in high-endurance titanium [1] or carbon fiber-based nonmagnetic materials is used conventionally to enhance the rotor strength of magnetoelectric excitation high-speed electric machines. Eddy currents induced by tooth harmonics are seen as a major flaw in weighty titanium bandage, while a widened mechanical gap between the rotor and the stator is the principal shortcoming of nonmagnetic bandage, as it reduces magnetic induction values within the gaps. This article discusses a way to increase the rotor top rotational speed (the radial speed) through a dovetail permanent magnet joint solution without using additional titanium or carbon fiber bandage.

Stress Intensity factors of a semi-elliptical crack in a Compressor blade of dovetail joint through numerical approach

Induced fatigue has led to a large number of deviations of service failures in a wide range of applications, where the deterioration of properties occurs due to the slipping between surfaces at a small displacement. In this article, a numerical simulation of a semi-elliptical crack in the dovetail joint of the compressor was performed to understand the destruction of the blade due to the stress contour in the contact area. A three-dimensional crack is modelled using the ANSYS Finite Element Analysis program, and the blade profile is modelled by CATIA V5R20 software. The study considers a model of an open semi-elliptical crack, and the parameters of the movement of the crack tip are estimated using three-dimensional singular elements of the crack tip in ANSYS. Initially, a three-dimensional finite element model of a compressor blade with a dovetail contact area was simulated in CATIA V5 and analysed in the ANSYS working environment to determine the maximum principal stresses in the crack-free region. After the crack front has been precisely identified and confirmed, fracture modelling is used to determine the impact of crack size with one side, as well as rotation speed, on fracture parameters (stress intensity factors).

Fatigue performance of UHPC bridge deck system with field-cast dovetail joint

The Fifth Nanjing Yangtze River Bridge had adopted accelerated bridge construction utilizing precast systems to connect the prefabricated plate with the cast-in-place ultra-high performance concrete (UHPC) wet joint. Wet joints are prone to crack under fatigue load. In this study, the steel wire mesh (SWM) treatment method was adopted to enhance the interface crack resistance, and add coarse aggregate (CA) to UHPC to reduce cost. Decks were tested under static and fatigue loadings to study the effects of CA, SWM interface treatment, and stress level on fatigue performance. Results indicate that the fatigue performance of wet joints using UHPC with CA was similar to that using regular UHPC. Dovetail wet joints using SWM interface treatment effectively guarantee the bridging effect of the fiber at the interface and disperse fatigue cracks. Overloading affected the fatigue performance, and the fatigue damage was linear to the upper limit of stress when the stress ratio was fixed. Secant stiffness was used to evaluate the fatigue damage of decks, and the calculated damage was in good agreement with the actual bearing capacity loss. This study verified that the innovative dovetail wet joint is practical, economical, and guarantees fatigue performance.

Finite Element Analysis of a Controlled Dynamization Device for External Circular Fixation.

Objective To virtually prototype a device for external circular fixation of long bone fractures with controlled dynamization made of two different materials and predict their mechanical behavior by using the finite element analysis (FEA) method. Method A software was used for 3D modeling two metal parts closely attached by a sliding dovetail joint and a high-density silicone damper. Distinctive FEAs were simulated by considering two different materials (stainless steel or titanium), modes (locked or dynamized) and loading conditions (static/point or dynamic/0.5 sec) with uniform 150 kg axial load on top of the device. Results The finite elements (FEs) model presented 81,872 nodes and 45,922 elements. Considering stainless steel, the maximum stress peak (140.98 MPa) was reached with the device locked under static loading, while the greatest displacement (2.415 × 10 −3 mm) was observed with the device locked and under dynamic loading. Regarding titanium, the device presented the maximum stress peak (141.45 MPa) under static loading and with the device locked, while the greatest displacement (3.975 × 10 −3 mm) was found with the device locked and under dynamic loading. Conclusion The prototyped device played the role of stress support with acceptable deformation in both locked and dynamized modes and may be fabricated with both stainless steel and titanium.

A study on the vibration dissipation mechanism of the rotating blade with dovetail joint

The vibration dissipation mechanism of the rotating blade with a dovetail joint is studied in this paper. Dry friction damping plays an indispensable role in the direction of vibration reduction. The vibration level is reduced by consuming the total energy of the turbine blade with the dry friction device on the blade-root in the paper. The mechanism of the vibration reduction is revealed by the variation of the friction force and the energy dissipation ratio of dry friction. In this paper, the flexible blade with a dovetail interface feature is discretized by using the spatial beam element based on the finite element theory. Then the classical Coulomb-spring friction model is introduced to obtain the dry friction model on the contact interfaces of the tenon-mortise structure. What is more, the effects of the system parameters (such as the rotating speed, the friction coefficient, the installation angle of the tenon) and the excitation level on blade damping characteristics are discussed, respectively. The results show that the variation of the system parameters leads to a significant change of damping characteristics of the blade. The variation of the tangential stiffness and the position of the external excitation will affect the nonlinear characteristics and vibration damping characteristics.

INVESTIGATING POSSIBILITIES OF CRACK INITIATION LIFE EXTENSION IN JET ENGINES COMPRESSOR DISKS

This paper deals with jet engines compressor disks which have dovetail joints with blades. A compressor disk with reduced fatigue resistance was taken as an example. Two simplified conceptual solutions of the dovetail joint with blades were devised. Based on the low cycle fatigue theory, the crack initiation life of their critical parts with newly-proposed transition rounding at the bottom of dovetail grooves was estimated. Two different flank angles in the dovetail grooves (60° in the critical part that belongs to the first dovetail joint conceptual solution and 55° in the critical part that belongs to the second dovetail joint conceptual solution), two different aviation steels selected for workmanship (13H11N2V2MF and AISI 304 steel) and two load histories (load history LH1 and load history LH2), were taken into account. By load history LH2 an overload of the critical parts was simulated. The results of crack initiation life estimation of the critical parts in the dovetail joint conceptual solutions show that there is a possibility for the crack initiation life extension of the observed compressor disk. In all analyzed variants, it has been shown that the critical part in the second dovetail joint conceptual solution has longer crack initiation life than the critical part in the first dovetail joint conceptual solution. For example, the critical part in the second dovetail joint conceptual solution made of AISI 304 steel, in the case of load history LH1 has 141.55% longer crack initiation life than the critical part in the first dovetail joint conceptual solution made of 13H11N2V2MF steel. In the case of load history LH2 (an overload case) that percent is greater and amounts to 173.15%.

Joint identification through hybrid models improved by correlations

In mechanical systems coupled with joints, accurate prediction of the joint characteristics is extremely important. Despite years of research, a lot is yet to be learnt about the joints’ interface dynamics. The problem becomes even more difficult when the interface Degrees-of-Freedom (DoF) are inaccessible for Frequency Response Function (FRF) measurements. This is, for example, the case of bladed-disk systems with dove-tail or fir-tree type joints. Therefore, an FRF based expansion method called System Equivalent Model Mixing (SEMM) is used to obtain expanded interface dynamics. The method uses numerical and experimental sub-models of each component and their assembly to produce the respective expanded or hybrid sub-models. By applying substructure decoupling to these sub-models, the joint can be identified. However, the joint can be noisy due to expansion and measurement errors which propagate to the hybrid sub-models.In this paper, a correlation based approach is proposed in the SEMM method wherein the quality of the expanded sub-models is improved. In this new approach, several expanded models are generated systematically using different combinations of the experimental FRFs and computing a parameter, Frequency Response Assurance Criteria (FRAC), to evaluate quality of the contribution of the different measurements. The lowest correlated channels or FRFs can be filtered out based on a certain threshold value of FRAC. Using the improved hybrid sub-models, the joint identification also shows a remarkable improvement. The test object for the method is an assembly of disk and one blade with a dove-tail joint.

Comparative study on the tensile performance of box frames constructed by keyed joints and dovetail joints

The box frame is a common structure in modern furniture, especially for cabinets. Accordingly, the joint contact force of the frame is important in evaluating the stability of classified furniture. In this study, a new type of keyed joint was proposed to alter the dovetail joint used in box frame structures. The tensile strength of the dovetail joint and the keyed joint in the frame were evaluated, and the contact forces and failure modes of these two joints were compared. Three levels (T1, T2, and T3) were proposed for the ratio of groove depth (D) to inclined contact surface height (H), under the condition of the same joint spacing and inclination angle considering the effects of keyed joint size on the contact force. Meanwhile, experimental analysis was performed on both sides (S1 and S2) of the dovetail joint. Results showed that the contact force of the joint under the gluing condition decreased in the order of S2 > T2 > T3 > S1 > T1. In terms of failure modes, the keyed joint could be maintained in good condition, whereas failure of the dovetail joint always occurred at the root of the tenon in the S1 direction.

Furniture Construction Skill Gap Analysis among Technical College Teachers in Zamfara and Katsina States

This study identified the practical skills possessed and skills required by furniture construction teachers in Zamfara and Katsina State, Nigeria. Three research questions that sort to determine the skills needs of furniture construction teachers were answered and one hypothesis was tested at 0.05 level of significance. A descriptive survey research design was adopted for the study. The population for the study was 42 teachers. A structured questionnaire was used to gather data from the 42 woodwork furniture construction teachers. The instrument had a reliability coefficient of 0.89 using Cronbach Alpa statistic. Mean and standard deviation was used to answer research questions and a t-test was used to test the hypothesis using the IBM SPSS version 20. The findings of the study revealed that the respondents require skills on the ability to hold a saw with fore-finger straight out on one side of the handle, the ability to follow the “FEWTEL” method in preparing a piece of wood require further training, setting sliding bevel when marking out dovetail joint and selection of the right adhesive according to the purpose and type of wood as well as amount of force the adhesive would be subjected to required skills. It was recommended that; government should provide opportunities for furniture construction teachers to go on further training on the modern furniture construction technology required. The identified skills required by teachers of furniture construction should form the basis for the up-skill workshop to be organized as in-house training.

Numerical and experimental investigation on the elastic stiffness of glued dovetail joints

This study investigates the stiffness of dovetail joints by both numerical and experimental methods. Test specimens were made of Spruce (Picea abies L) and Beech (Fagus Silvatica L) wood, which were bonded with polyurethane (PUR) and polyvinyl acetate (PVAc) adhesives into dovetail joints. To determine the mechanical behavior, the joints were loaded according to grain direction under compressive and tensile load. The results of the experiment indicated that, under compression load, beech wood bonded with polyvinyl acetate (PVAc) adhesive had maximum elastic stiffness. Based on the experimental results, a numerical model using the finite element method (FEM) was developed by the Abaqus program to predict the stiffness of dovetail joints under compressive and tensile load. For numerical analysis, the assumption was made that arm deflection was caused by a displacement in the supports. The value of deflection corresponds to the limit of linear elasticity and the value of the force reduced stresses, which was determined on the basis of deflections. A cohesive zone was developed, which shows stress behavior under compressive and tensile load. A positive correlation was found between the numerical model and experimental study.

On an improved adaptive reduced-order model for the computation of steady-state vibrations in large-scale non-conservative systems with friction joints

Joints are commonly used in many large-scale engineering systems to ease assembly, and ensure structural integrity and effective load transmission. Most joints are designed around friction interfaces, which can transmit large static forces, but tend to introduce stick-slip transition during vibrations, leading to a nonlinear dynamic system. Tools for the complex numerical prediction of such nonlinear systems are available today, but their use for large-scale applications is regularly prevented by high computational cost. To address this issue, a novel adaptive reduced-order model (ROM) has recently been developed, significantly decreasing the computational time for such high fidelity simulations. Although highly effective, significant improvements to the proposed approach is presented and demonstrated in this paper, further increasing the efficiency of the ROM. An energy-based error estimator was developed and integrated into the nonlinear spectral analysis, leading to a significantly higher computational speed by removing insignificant static modes from the stuck contact nodes in the original reduced basis, and improving the computational accuracy by eliminating numerical noise. The effectiveness of the new approach was shown on an industrial-scale fan blades system with a dovetail joints, showing that the improved adaptive method can be 2–3 times more computationally efficient than the original adaptive method especially at high excitation levels but also effectively improve the accuracy of the original method.

Mechanical and microstructure characteristics of heat-treated of high-Cr WI and AISI4140 steel bimetal beams

Heat treatments are considered as one of the most important methods used to make significant changes in the microstructure of the metallic materials and their alloys, which makes it possible to change the external behavior and properties of these materials. The effect of heat treatment at 900°C on the microstructure, hardness and flexural behavior of bimetal beams has been studied in the present work. The bimetal beams composed of a high-Cr WCI as a wear-resistant part and an AISI4140 steel as a ductile part were fabricated. The two parts of bimetal castings are joined together by means of dovetail joint and/or connector pins. The present experimental and numerical results revealed that all bimetal beams exhibited flexural strength, toughness and maximum deflection higher than those of high-Cr WI specimen and lower than those of AISI4140 specimen in heat treated conditions. Heat treatment of the bimetal casting beams produced significant improvements in both hardness and flexural strength of high-Cr WI and AISI4140 steel. This is due to the formation of secondary carbides in the martensitic matrix surrounded by a network of M7C3 carbides in high-Cr WI, and formation of fine pearlite with proeutectoid α at grain boundaries for AISI4140 steel as revealed by SEM and an optical metallography. Bimetal beam with 12-connector pins (BI12CONN) as a mechanical joint exhibited the highest flexural strength and toughness compared with the other bimetal beams after heat treatment.

Dynamic and static comparison of beech wood dovetail, tongue and groove, halving, and dowel joints

Dynamic and static elastic properties beech wood joints were assessed. Conventional joints, namely dovetail, tongue and groove, dowel, and halving joints were prepared with beech wood (Fagus orientalis Lipsky) using polyvinyl acetate and cyanoacrylate adhesives. The results of the dynamic and static modulus of elasticity of the joints in this research indicated the highest reduction trends in halving, dowel, tongue and groove, and dovetail joints, respectively. The modulus of dovetail joint elasticity, its homogeneous joint texture, and lack of an extended adhesive line, corresponded to that of the jointed samples. The average static modulus of elasticity was approximately 10.5% lower than that of the dynamic modulus of elasticity. The results of the Student’s t-test indicated a significant difference between the mean of dynamic and the mean of static modulus of elasticity, significance at 5% level and the Pearson correlation test indicated that the dynamic and static modulus of elasticity of the samples were significant at the 5% level and indicated a positive correlation. Based on the observed correlation in the dynamic and static tests’ results, using these methods, dynamic assessment of NDTs may be regarded as an appropriate alternative in standardizing destructive static testing for wood assessment and categorization.

Experimental and computational study on mechanical behaviour of carpentry corner log joints

This work concerns experimental and numerical research on carpentry joints used in historic wooden buildings in southeastern Poland and western Ukraine. These structures are mainly sacred buildings, and the types of corner log joints characteristic of this region are primarily saddle-notch and dovetail joints; thus, these two types of joints were analysed in this study.The modelling of historic timber structures is a complex issue, so the following steps are necessary to obtain accurate solutions: verification, validation and uncertainty quantification. The first and third steps were performed in a previous study, so the current research aimed to validate the numerical models and perform simulations of carpentry joints. Herein, the authors created finite element models of two types of joints and subsequently analysed the mechanical behaviour of these joints.Due to issues concerning model validation, the authors designed a testing stand for corner joints, which formed a part of a biaxial testing machine. The joints were subjected to horizontal loads (deformations), which may cause damage to the connection. Thus, special parts were designed for the stand, which made it possible to fix the joint and prevented eccentric forces that could possibly damage the machine during testing.The authors presented the differences and similarities in the behaviour of both types of joints, emphasizing the corresponding advantages and disadvantages. In addition, the authors determined which type of joint was the most susceptible to damage and what elements failed first.This paper also showed the complexity of modelling timber structures and the accuracy of the proposed numerical models for both types of joints through comparisons of the numerical and experimental results. This work primary addressed the problems in accurately reflecting material, load and boundary conditions in numerical modelling of tested carpentry corner log joints.

Analysis on vibration reduction of a rotating dovetailed blade with underplatform damper and installation preload

The vibration reduction characteristics of the flexible blade with a dovetail joint and underplatform damper are studied in this paper. Considering the influence of the platform mass on the inherent characteristics of the blade, this paper regards the underplatform as a particle with mass. Moreover, two types of friction models are introduced on the contact interfaces of the blade. Meanwhile, the normal pressure of the contact interfaces will change with the rotating speed of the blade. Also, the dynamical equation for the rotating blade is established based on the finite element method. The nonlinear friction force on the contact interface is brought into the dynamical equation, and the vibration response of the blade is solved. The effects of the rotating speed, the initial preload, and the contact angle of the underplatform on the vibration reduction characteristic of the blade are investigated.

Experimental study of the mechanical behaviour of a new extruded earth block masonry

The aim of this research is to investigate, through the Digital Image Correlation (DIC) technique, the mechanical performance of a new type of earth masonry, built with extruded blocks and characterized by dovetail horizontally staggered bed joints. The experimental program consists of two levels of investigations: (i) preliminary phase on components, (ii) compression, diagonal compression and combined shear-compression tests on 12 wallettes. Regarding the components, results showed that the mean compressive strength of the earth block was low (3.5 MPa) with respect to traditional bricks and similar to adobe blocks. The dovetail joints were effective in their joining role showing a rather good strength (2.4 MPa) when tested in triplet configuration. Regarding the wallettes, the DIC highlighted failure modes complying with the ones of a traditional masonry under shear, while it showed a “column behaviour” with vertical sliding under compressive tests. Fragile failures occurred during the diagonal compression test. DIC revealed to be a promising technique to recover the full-field strain and crack maps.

Aspects of Fretting Fatigue Finite Element Modelling

Fretting fatigue is a type of failure that may affect various mechanical components, such as bolted or dovetail joints, press-fitted shafts, couplings, and ropes. Due to its importance, many researchers have carried out experimental tests and analytical and numerical modelling, so that the phenomena that govern the failure process can be understood or appropriately modelled. Consequently, the performance of systems subjected to fretting fatigue can be predicted and improved. This paper discusses different aspects related to the finite element modelling of fretting fatigue. It presents common experimental configurations and the analytical solutions for cylindrical contact. Then, it discusses aspects of fretting fatigue crack initiation, such as crack location, orientation, and length, as well as stress averaging approaches. Then, it deals with the propagation stage; crack face interaction, orientation criteria, and crack growth rate are discussed. Lastly, additional aspects of recent research on fretting fatigue are reviewed: out-of-phase loading, cohesive zone modelling, wear effects, heterogeneity, and crystal orientation. Fretting fatigue is a phenomenon not well understood, and much more research is needed so that its understanding is increased and proper criteria and laws may be available for different cases.