Asymmetric Joints Research Articles

An experimental-cohesive zone model approach to predict fatigue life of adhesive joints with varying modes of loading and joint configurations for automotive applications

ABSTRACT Predictive fatigue life models of adhesive joints are necessary to enable the assessment of automotive-bonded structures while reducing costly experimental testing. However, contemporary models have typically been calibrated for specific joint configurations and modes of loading, limiting their applicability to large-scale structures. Additionally, available models are based on simulation of cumulative fatigue cycling, making them computationally prohibitive. In the current study, cross-tension (CT) (load angles of 0°, 45°, and 90°) and single-lap shear joint (SLJ) configurations were bonded using an epoxy adhesive (BetaGuard CI6125R; PPG, France) used in automotive production (one part) and tested under fatigue cyclic loading. A total of nine joint configurations, having symmetrical (same material and thickness) and asymmetrical (dissimilar material or unequal thickness) joints, were tested. Fatigue tests at load levels between 25% and 75% of the static peak load were performed until joint failure or to runout (two million load cycles). The static tests of the joints were simulated to failure using finite element (FE) models with the cohesive zone method (CZM). The maximum strain energy release rates ( G max ) were calculated within the adhesive bond line at static loads corresponding to the peak loads of the fatigue tests. The G max values, computed from single cycle, specimen-specific FE simulations, were correlated with the measured fatigue life ( N f ) of the adhesive joints with varying modes of loading and joint configurations. The fatigue life prediction model, based on G max − N f correlation and following a crack propagation approach, predicted the cycles to failure for 85% of the fatigue tests, and 81% of the independent validation tests. The proposed fatigue life prediction approach provides computational efficiency and large-scale compatibility.

Component method for bolted SHS end plate splice joints loaded in tension

Bolted end plate connections are traditional solutions for splice joints with square hollow sections (SHS). A cover plate could be used on one side or two adjacent sides of SHS where the end plate is flushed, resulting in two types of asymmetric splice joints. The advantage of the asymmetric joints is that no space is required between the façade panel and the member surface whilst the easy assembly feature remains. The component method is used to design the bolted end plate connection, as stipulated in prEN 1993–1–8. However, the design rule is only available for connections with open cross-sections. In this paper, a modified component method for predicting the tensile resistance (end plate fails with failure mode 1 according to prEN 1993–1–8) and stiffness of the asymmetric bolted SHS end plate splice joints is proposed. First, a parametric study is carried out to develop the component method for the traditional symmetric bolted SHS end plate splices based on the validated finite element (FE) model. Next, a simplified two-dimensional FE model is employed to evaluate the effect of the asymmetric feature on the stiffness of the joint. Finally, a parametric study is carried out on two types of asymmetric joints to validate the interaction model of individual components. The resistance and stiffness of the asymmetric end plate splice joints are well predicted using the modified component method.

The role of overstrength in welded joints for rebar substitution in damaged RC columns

Rehabilitating corroded or seismically damaged reinforced concrete (RC) bridge columns often involves replacing the longitudinal steel rebar. Welded joints offer a practical and efficient in-situ solution for connecting new rebar segments to existing undamaged rebar, even with irregularities in the steel reinforcement. However, traditional approaches to rebar joint welding have paid little attention to the overstrength of the welding seam, which can result in a brittle response. Properly designing such joints should aim for a ductile rebar failure. However, in-situ rehabilitation solutions often require reducing the seam length to save time and material costs and, not secondarily, avoiding the plastic hinge formation in the rehabilitated column. Therefore, providing the seam with adequate overstrength is crucial to achieving a ductile failure of the welded joint. This study presents an experimental investigation into the most effective methods for connecting existing and new rebar segments through welding, addressing on-site welding challenges such as limited operational space and weld orientation. Over 100 tensile tests have been conducted at Fuzhou University’s laboratory in China to understand the response of nine welded joints. Among indirect butt joints, the study identifies two performance groups based on the ductile failure rate as the welding seams reduce. The symmetry of the joint and the presence of additional direct butt welding also in asymmetric joints can significantly improve the joint performance, determining a ductile failure with minimal welding lengths. In a second step, following a probabilistic approach, the study assesses the overstrength of indirect butt joints as a function of seam length for the two identified performance groups. Empirical failure probabilities of the rebar and the seam are estimated to fit probability density functions representative of the tensile strength of the rebar and the seam. Based on a target reliability class, the overstrength factors are estimated.

Improved mechanical performance of quasi-cubic lattice metamaterials with asymmetric joints

In this paper, we propose a simple method for the modification of the unit cells in the lattice metamaterials that provides an improvement of their impact strength. The idea is based on the introduction of small mutual offsets of the interconnected struts inside the unit cells. In such way, the joints between the struts become asymmetric and the overall geometry of the unit cells can be defined as the quasi-cubic with the axis of chirality. Considering four types of cubic lattices with BCC, BCT, FCC and octahedron structures, we modified their geometry and investigated the influence of the offsets and the unit cell size on the overall performance in static and dynamic tests. From the experiments we found that the small offsets (less than the strut diameter) can allow to increase the impact strength of 3d-printed polymeric specimens in 1.5–3 times remaining almost the same density and static mechanical properties. Based on the numerical simulations, we show that the explanation of the observed phenomena can be related to the increase of plastic deformations and damage accumulation in the unit-cells with asymmetric joints leading to the transition from the quasi-brittle to the ductile type of fracture in tested specimens.

Experimental comparison between threaded‐bars and single‐bolts end plate asymmetrical steel joints

AbstractEnd plate beam‐column bolted joints are widely used in the field of steel structures. The usual configuration consists of individual bolts that join the end plate of the beam with the column flange. Usually, the use of stiffeners is needed in this type of joints, in order to reinforce the tension and compression zones of the column web, and to avoid local buckling problems.This configuration, applied to asymmetric connections, gives rise to the appearance of shear stresses in the column web, even with symmetric loading conditions on both sides of the connection.The method proposed in this work to improve the behavior of end plate asymmetrical steel joints, without using welded stiffeners (which significantly increases the cost of the joint), consists in using threaded bars as joining elements, instead of single bolts. Threaded bars have several purposes: to create the joint itself, to reinforce the tension and compression zones, and to reduce the shear stresses in the column web panel.In the present work, two end plate steel joints made up of an HEA200 column, and IPE200 and IPE300 beams have been tested. One of them with threaded bars with double nuts (internal and external) in the traction and compression zones, and the other one with single bolts.Symmetrical forces have been applied at the ends of the beams, subjecting the joints to symmetrical bending moments on both sides of the connection. The tests have been instrumented through the use of load cells, displacement sensors and inclinometers. The results show an important increase in the stiffness and the resistance of the joint with threaded bars, compared with the single bolts joint.This work will serve as the basis for the calibration of the corresponding finite element models, and the subsequent parametric study of this type of joints.

The Role of CD1 Gene Polymorphism in the Genetic Susceptibility to Spondyloarthropathies in the Moroccan Population and the Possible Cross-Link with Celiac Disease.

Spondyloarthropathies (SpA) are a group of chronic inflammatory disorders usually affecting the axial spine and asymmetrical peripheral joints. Strong evidence links genetic and environmental factors to SpA pathogenesis. The HLA-B27 is the most important genetic factor associated with SpA. Nevertheless, the involvement of other HLA and non-HLA loci has been also reported. Some patients with SpA may also manifest features of celiac disease (CeD), thus suggesting a genetic overlap across these autoimmune diseases. Recently, CD1 glycoproteins, a class of molecules able to bind and present non peptidic antigens to T cells, aroused interest for their contribution to the pathogenesis of CeD. Therefore, to evaluate whether functional polymorphisms of CD1A and E genes also influence susceptibility to SpA, we analyzed 86 patients from Morocco affected by SpA and 51 healthy controls, using direct sequencing analysis. An increase of CD1E*01/01 homozygous genotype (p = 0.046) was found in SpA, compared with controls. CD1E*01/01 genotype was associated particularly to patients with sacroiliac joints/spine/peripheral joints pain (p = 0.0068), while a decrease of CD1E*01/02 genotype was evidenced compared to controls (p = 0.0065). Results from haplotypes analysis demonstrated that CD1A*02-E*02 decreased the risk of SpA, while CD1A*02-E*01 increased risk to develop disease. Our data indicate a relationship between CD1 genes and susceptibility to SpA in the Moroccan population and suggest the existence of shared genetic risk loci across SpA and CeD that might be useful to explain common pathogenetic features and define novel therapeutic strategies.

Prediction of bonded asymmetric metallic cross-tension and single lap shear joints using finite element model with material-level adhesive properties and cohesive zone method

Predictive finite element (FE) models of adhesive joints are needed to enable the design and evaluation of adhesively joined structures, particularly large-scale structures that may be costly to assess experimentally. Although models calibrated to coupon-level tests have provided an important first-step, models based on material-level characterization are needed to enable joint assessment in complex modes of loading. In the present study, a structural epoxy adhesive was characterized using rigid double cantilever (Mode I) and bonded shear (Mode II) specimens to provide material-level input properties. Three single-lap shear (SLJ) and seven cross-tension (CT) specimen configurations were fabricated with aluminum and steel sheet materials. The specimens included symmetrical (the same adherend material and thickness) and asymmetrical (dissimilar adherend material or unequal thickness) configurations, with three loading angles (0°, 45°, 90°) for the CT specimens. Finite element models of the SLJ and CT specimens were developed using Cohesive Zone Modeling for the adhesive, with properties determined from the Mode I and Mode II characterization tests. The FE models of the SLJ and CT test specimens predicted the peak load within an average difference of 2%–19%. The joint strength varied between different test configurations, owing to adherend deformation, load eccentricity and mixed-mode loading. Importantly, the model parameters were not calibrated to the SLJ and CT tests. The FE models were able to predict joint response for varying test specimen geometry, adherend thickness, adherend material, and modes of loading.

Effect of rotational speed on the microstructure and mechanical properties of rotary friction welded AISI 1018/AISI 1020 asymmetrical joints

Abstract Asymmetrical joints (joining of the plate with rod) were joined using traditional fusion welding processes. However, the usage of unsuitable filler wire tends to lower weld penetration over the material surface, which also results in the attainment of hot or solidification cracks over the weld surface. To overcome these issues, solid-state welding processes are preferable. This study investigates the rotary friction welding (RFW) of AISI 1018 low carbon steel plate with AISI 1020 low carbon steel rod of asymmetrical joints. The friction welding process parameters such as rotational speed were taken as variable, and other parameters like friction pressure, forging pressure, friction time, and forging time were kept constant in this investigation. The impact of rotational speed on macrostructure, microstructure, and mechanical characteristics of joints such as microhardness, tensile strength, and fractography studies was analyzed. The fractured surface of the tensile specimen was examined through a scanning electron microscope (SEM). The maximum tensile strength of the joint about 452 MPa was observed. Maximum hardness at the weld interface was perceived at about 252Hv. Increasing rotational speed tends to increase the strength of the asymmetrical steel joints in rotary friction welding.

Mechanical properties of coated fabric membranes at high temperature

A model about the strength of polyvinyl chloride coated polyester at high temperature was proposed in this paper. The model can predict the warp-direction strength, weft-direction strength, and off-axis strength at high temperatures according to the uniaxial tensile strength in warp direction at room temperature. In this paper, the strength model of coated fabric membrane bearing biaxial tension was established by off-axis tensile test. Next, the strength of weld joints of coated fabric membrane at normal and high temperature were compared. Then, a strength predicting method for symmetric and asymmetric weld joints at high temperatures was proposed. Finally, the relation between temperature and fracture energy of weld seam was proposed.

Hysteretic Behavior on Asymmetrical Composite Joints with Concrete-Filled Steel Tube Columns and Unequal High Steel Beams

In order to acquire the hysteretic behavior of the asymmetrical composite joints with concrete-filled steel tube (CFST) columns and unequal high steel beams, 36 full-scale composite joints were designed, and the CFST hoop coefficient (ξ), axial compression ratio (n0), concrete cube compressive strength (fcuk), steel tube strength (fyk), beam, and column section size were taken as the main control parameters. Based on nonlinear constitutive models of concrete and the double broken-line stress-hardening constitutive model of steel, and by introducing the symmetric contact element and multi-point constraint (MPC), reduced-scale composite joints were simulated by ABAQUS software. By comparing with the test curves, the rationality of the modeling method was verified. The influence of various parameters on the seismic performance of the full-scale asymmetrical composite joints was investigated. The results show that with the increasing of fcuk, the peak load (Pmax) and ductility of the specimens gradually increased. With the increasing of n0, the Pmax of the specimens gradually increases firstly and then gradually decreases after reaching a peak point. The composite joints have good energy dissipation capacity and the characteristic of stiffness degradation. The oblique struts force mechanism in the full-scale asymmetrical composite joint domain is proposed. By introducing influence coefficients (ξ1 and ξ2), the expression of shear bearing capacity of composite joints is obtained by statistical regression, which can provide theoretical support for the seismic design of asymmetrical composite joints.

Effect of Facet Tropism on Postoperative Cervical Range of Motion After Single-Level Cervical Disc Arthroplasty.

Study Design:Retrospective analysis.Objectives:Cervical disc arthroplasty (CDA) was designed to replace the degenerated disc with the prosthesis to preserve cervical motion. The commonly used artificial discs are designed symmetric, whereas the facet joints were reported to be asymmetric in many people. This study aimed to evaluate the effect of facet tropism on the cervical range of motion (ROM) after single-level CDA using Prestige LP.Methods:A total of 90 patients who underwent single-level CDA using Prestige LP from 2012 to 2017 were retrospectively reviewed. Radiographs were taken at each time point to measure the C2-C7 ROM and the ROM at the surgical segment. The pre-operation CT scans were utilized to reconstruct and calculate the angular direction of facet joints with respect to transverse, coronal, and sagittal reference planes. Facet tropism above 7° was defined as facet joint asymmetry.Results:No significant difference was found in flexion-extension C2-C7 ROM or ROM at the surgical segment between patients with symmetric and asymmetric fact joints regarding the sagittal plane. Patients with coronal asymmetric facet joints had lower flexion-extension ROM at the surgical level. Patients with transverse asymmetric facet joints had both lower flexion-extension C2-C7 ROM and ROM at the surgical level. After CDA surgery, patients obtained good clinical outcomes including increased Japanese Orthopedic Association (JOA) and decreased Neck Disability Index (NDI) as well as Visual Analogue Scale (VAS).Conclusion:The coronal and transverse tropism seemed to be correlated with decreased flexion-extension ROM after CDA using Prestige LP.

A Case of Reactive Arthritis Presenting with Ocular Symptoms

Reactive Arthritis (RA), formerly known as Reiter’s Syndrome, refers to non-septic joint inflammation that develops in reaction to an infection in another part of the body. RA is often characterized by a classic triad of symptoms: inflammation of multiple asymmetric joints usually in the lower limbs, inflammation of the eyes in the form of conjunctivitis or uveitis and urethritis in men or cervicitis in women. These three symptoms may occur separately, all at once or not at all.

Development of a 7-DoF Power Soft Robot driven by Hydraulic Artificial Muscles

The mechanisms of the current robotics are completely different from the muscle driving mechanisms of humans or animals. The 7-DOF power soft robot arm driven by hydraulic artificial muscles developed in this study can potentially achieve the coexistence of strength and softness while having motion characteristics close to those of humans. This robot has two antagonistic joints on the shoulder, two asymmetrical antagonistic joints on the upper arm and the lower arm, and the wrist and elbow have rotational pull-wire drive joints, a total of 29 hydraulic artificial muscles.

Shear Mechanical Properties of Artificial Rock Specimen with Symmetrical and Asymmetric Toothed Structural Joints

Direct shear tests on cement mortar samples with symmetrical and asymmetric toothed structural joints were conducted in this study. The main objective is to study the effect of the left undulation angle (i1), the right undulation angle (i2), and the length (l) of the undulation body on the shear properties of artificial jointed rock samples. The test results show that for artificial rock samples with through-symmetrical toothed structural joints (i1 = i2), there is a significant increase in the shear strength and cohesion c of the test specimens when i1 remains constant and l gradually increases. An increase occurs in the shear strength and internal friction angle φ when there is a gradual increase in i1 and l remains constant. For those samples with through-asymmetrical toothed structural joints (i1 ≠ i2), there is a significant increase in the shear strength and cohesion c of the test specimens when i1 remains constant and l gradually increases, and the shear strength of the specimen first increases and then decreases when i1 increases from 15° to 75° and l remains constant.

Design and Kinematics Analysis of a Robotic Pediatric Neuroendoscope Tool Body

Endoscopy is often used to treat hydrocephalus, a common pediatric neurosurgical condition. Rigid endoscopic tools used in these procedures have many limitations. In this article, we propose four novel designs for a steerable two degree-of-freedom robotic tool body to be deployed through a rigid endoscope and a handheld controller for such a tool body. Each of these designs make use of tendon-driven joints known as asymmetric notch joints, while varying tendon routing techniques. Furthermore, we design a compact handheld controller for this steerable tool body, which consists of dc motors driving lead screws to actuate the tendons for each of the robot's joints. A disturbance observer-based control system for these motors is designed to allow the motor to reach the desired tendon displacements under various loading conditions. Next, we analyze the kinematics of the bidirectional asymmetric notch joint, deriving a relationship between the joint angle and corresponding tendon displacement. Finally, we test each of our four proposed designs for interjoint coupling and provide some insights into the results of our tests. We find that tendon routing strategies play an important role in minimizing tendon coupling for meso-scale continuum tendon-driven robots and combining the properties of each of these asymmetric joints can prove to be beneficial in improving the performance of such two degree-of-freedom robots.

Mode I fracture toughness of asymmetric metal-composite adhesive joints

In this work, the mode I fracture toughness of dissimilar metal-composite adhesive joints is experimentally investigated using the double cantilever beam (DCB) test. The particular joint under study is resulted by the adhesive joining of a thin titanium sheet with a thin carbon fiber reinforced plastic (CFRP) laminate and is envisioned to be implemented in the hybrid laminar flow control system of future aircraft. Four different industrial technologies for the joining of the titanium and CFRP adherents are evaluated/compared; co-bonding with and without adhesive and secondary bonding using either thermoset or thermoplastic CFRP. The vacuum-assisted resin transfer molding (VARTM) technique is employed for the manufacturing of the panels. After manufacturing, the panels are cut into test specimens that, because they are too thin (approximately 2.4 mm thick), needed to be stiffened from both titanium and composite sides with two aluminum backing beams to ensure the non-yielding of the titanium during the subsequent DCB tests. Towards the determination of the fracture toughness of the joint from the experimental data, an analytical model recently developed by the authors, that considers the bending-extension coupling of both sub-laminates constituting the test specimen as well as the manufacturing-induced residual thermal stresses, is applied. For the four manufacturing options (MO) investigated, the load-displacement behaviors, failure patterns, and fracture toughness performances are presented and compared.

Metamodelling of stiffness matrices for 2D welded asymmetric steel joints

Beam-column steel joints usually have a semi-rigid behaviour, and this must be taken into account when carrying out a global analysis of the structure. Rotational springs at each side of the joint are commonly used to simulate this behaviour by means of the component method, but asymmetric welded beam-column steel joints are not included in the formulations of Eurocode 3. This research work proposes a new methodology to obtain the stiffness of welded asymmetrical beam-column steel joints, by means of a cruciform element of 4 nodes and 12 DOF, whose stiffness matrix is directly obtained by means of the meta-modelling of its elements using Kriging's method. The authors have carried out a wide study of 754 different asymmetric welded beam-column steel joints, whose finite element models have been analysed, and then the static condensation method has been used to obtain the equivalent condensed stiffness matrix (Kcond) of the cruciform element for the joints belonging to the training set. These matrices have been used to build the Kriging's model, and the rest of joints have been used for testing the method, which yields very good results. The use of meta-modelling methods to obtain the stiffness matrix of the joint is not only easier in its application than the component method, but it also leads to a formulation that is more accurate, and also takes into account the interactions between the different parts of the joint.

Mode II fracture toughness of asymmetric metal-composite adhesive joints

The paper presents an experimental investigation of the mode II fracture toughness behavior of dissimilar metal-composite adhesive joints using the end-notched flexure (ENF) test. The adhesive joint under study consists of a thin titanium sheet joined with a thin CFRP laminate and is envisioned tobe applied in the hybrid laminar flow control system of future aircraft. Four different industrial technologies for the manufacturing of the joint areevaluated; co-bonding with and without adhesive and secondary bonding using either a thermoset or a thermoplastic composite. The vacuum-assisted resin transfer molding (VARTM) technique is employed for the manufacturing of the titanium-CFRP joint. After manufacturing, the joint is stiffened from its both sides with two aluminum backing beams to prevent large deformations during the subsequent ENF tests. Towards the fracture toughness determination from the experimental data, an analytical model recently reported by the authors is applied; that model considers the bending-extension coupling of each sub-laminate of the joint as well as the effect of the manufacturing-induced residual thermal stresses. The load-displacement behaviors, failure patterns, and fracture toughness performances for each of the four manufacturing options (MO) investigated are presented and compared.

Direct analysis of steel frames with asymmetrical semi-rigid joints

Semi-rigid joints have been widely studied in literature in recent decades because they affect greatly the structural response of frames. In literature, the behavior of semi-rigid joints is commonly assumed to be identical under positive and negative moments which are obviously incorrect in many cases where joint details such as bolt arrangement or placement of haunch are vertically asymmetrical. This paper evaluates two common types of steel frames with asymmetrical beam-to-column joints by Direct Analysis allowing for plasticity. A refined design method of steel frames using a proposed simple forth order curved-quartic element with an integrated joint model allowing for asymmetrical geometric joint properties is presented. Furthermore, the ultimate behavior of six types of asymmetrical end-plate connections under positive and negative moment is examined by the Finite Element Method (FEM). The FEM results are further applied to the proposed design method with the curved-quartic element for Direct Analysis of two types of steel frames under dominant gravity or wind load. The ultimate frame behavior under the two different scenarios are examined with respect to their failure modes and considerably different structural performances of the frames were observed when compared with the identical frames designed with the traditional method where symmetrical joints characteristics were assumed. The finding of this research contributes to the design of steel frames as their asymmetrical beam-to-column joints lead to different frame behavior when under positive and negative moment and this aspect should be incorporated in the design and analysis of steel frames. This consideration of asymmetrical joint behavior is recommended to be highlighted in future design codes.

Er/Yb Codoped Double Clad Fiber Modal Interferometer and Its Application as Fiber Sensor

An Er/Yb codoped double clad fiber (EYDF) modal interferometer and its application as fiber sensor are proposed and demonstrated. It has the single mode fiber (SMF)-EYDF-SMF structure with two asymmetrical splice joints. The MI is sensitive to refractive index (RI) and temperature. Experimental results show that the pump power can tune its operation wavelength, and the higher power will lead to the more redshift of its transmission spectrum. What's more, appropriate change of RI can improve the wavelength tuning range induced by pump power. Moreover, its RI and thermal sensitivities are pump power dependent, and higher pump power will lead to its lower RI sensitivity and lower thermal sensitivity.