Joint Configuration Research Articles

Effect of heat input on corrosion behavior of automotive zinc-coated steel joint

Abstract Lately, coated steel sheets have replaced bare steel in the automotive sectors due to their corrosion protection. Among them, zinc-coated high strength interstitial free (HIF) steel is widely used due to its durability, formability, good surface finish, impact resistance, and corrosion resistance. However, joining galvannealed (GA) steel using conventional fusion welding processes is challenging as it results in porosity and potentially harmful fumes. To overcome these challenges, this work uses a pulse MIG (metal inert gas) brazing technique to join the HIF-GA steel sheet with a lap joint configuration utilizing Cu-Si base filler wire (CuSi3Mn1) in an argon atmosphere. The study aims to evaluate the effect of heat input on bead geometry and Zn degradation in MIG brazed joints by adjusting the current from 40 to 60 A and brazing speed from 400 to 500 mm min−1. It is observed that the heat input is inversely proportional to the wetting angle and directly proportional to the bead width, leg length, and cross-sectional area. Heat input influences Zn degradation on both the front (at the toe) and back sides of the lap joint. The corrosion behavior of joints is studied using an electrochemical test (in 3.5% NaCl solution) and a salt spray test (in 5% NaCl solution). Further, the Zn degradation is analyzed with EDS line scanning to understand the corrosion resistance of the MIG brazed joints. A potentiostatic polarization study is also conducted to determine the corrosion rate using a Tafel plot. It is found that the lowest corrosion rate in base metal (BM) increased from 0.88 to 12.26 mm year−1 with the increase in heat input from 61 to 113 J mm−1.

Design Concepts for Peel-Dominant Adhesive Joints in Aeronautic Applications

The adhesive bonding technique is employed from the aeronautical/aerospace industry to current house products. To comply with the requirements of distinct applications, different joint configurations are available to the designer. While single-lap joints (SLJ) are the most common in application and research, double-lap joints, scarf joints and T-joints find specific applications. T-joints are seldom studied in the literature, but these are used, for instance, in aircraft to bond the stiffener beams to the skin, or in the cars between the B-pillar and the rocker. Due to the high stress concentrations, T-joints often fail under average stresses much lower than the adhesive strengths, giving rise to the necessity for proper design and strength improvement methodologies. This work initially aims to validate the cohesive zone modelling (CZM) technique with experiments, and then use it to numerically evaluate and optimize the performance of T-joints subjected to peel loads. CZM is nowadays regarded as the most powerful strength prediction tool for adhesive joints, and can be a valuable tool to improve T-joints. Different features are addressed for a complete analysis: adhesive type, geometrical parameters, dual-adhesive technique for strength improvement, and composite joints. The evaluated geometrical parameters are the base adherend thickness (a), T-part thickness (t), overlap or bonding length (l) and curvature radius (r). As a result of this work, the model was successfully validated, and clear design guidelines were provided to define the ideal geometric and material (adhesive) conditions for best performance.

Design, development, and analysis of the lower body of next-generation 3D-printed humanoid research platform: PANDORA

AbstractThe main contribution of this paper is the design and development of the lower body of PANDORA (3D-Printed Autonomous humaNoid Developed for Open-source Research Applications), a new humanoid robotic platform implementing additive manufacturing techniques. The three joint configurations (hip, knee, and ankle) along with the major three structural parts (pelvis, thigh, and shin) of the lower body are discussed. The use of 3D printing and PLA+ material makes the robot an affordable solution for humanoid robotics research that gives a high power-to-weight ratio by significantly reducing the number of parts, as well as manufacturing and assembly time. The range of motion of the lower body of PANDORA has been investigated and is found to be comparable to a human lower body. Further, finite element analysis has been performed on the major parts of the lower body of PANDORA to check the structural integrity and to avoid catastrophic failures in the robot. The use of in-house developed actuators and robot electronics reduces the overall cost of the robot and makes PANDORA easily accessible to the research communities working in the field of humanoids. Overall, PANDORA has the potential for becoming popular between researchers and designers for investigating applications in the field of humanoid robotics, healthcare, and manufacturing, just to mention a few. The mechanical designs presented in this work are available open source to lower the knowledge barrier in developing and conducting research on bipedal robots.

Effect of Alloying Elements on Intermetallic Formation during Friction Stir Welding of Dissimilar Metals: A Critical Review on Aluminum/Steel

The main drawback of friction stir welding (FSW) dissimilar metals is the formation of intermetallic compounds (IMCs), which are brittle and affect the strength of the joint. The formation of these compounds is inevitable due to their low enthalpy of formation; however, their emergence is an indication of metallurgical bonding between dissimilar metals. This means that the determining factors of intermetallics should be optimal to ensure the formation of the joint and, at the same time, the performance of the joint. It is known that various parameters such as welding parameters, joint configuration, and tool geometry have an influence on the formation of these compounds. However, the influence of the base metal is not adequately addressed in the literature. The current review paper focuses on intermetallic formation during the friction stir welding of aluminum/steel (Al/St) alloys to explore how the types of alloys affect the thicknesses and morphologies of the intermetallics. Different structural steels and stainless steels were considered to see how they affect intermetallic formation when welded to different types of aluminum alloys. The thicknesses of the IMCs in the FSW of different aluminum/steel alloys were taken from the literature and averaged to provide insight into the contribution of the elements to IMC formation. Thermodynamic and kinetic analyses were used to explain this effect. Finally, the mechanism of intermetallic formation is explained to provide a useful guide for selecting dissimilar metals for welding using friction stir welding.

Design development and control of a shape memory alloy linear actuation based XYθ motion stage

This article addresses the development and trajectory tracking analysis of the three degrees of freedom Shape memory alloy (SMA) actuation-based 4- P PR motion stage. The developed motion stage is of four legs of the PPR (Prismatic-Prismatic-Revolute) configuration, having the first prismatic joint as the active joint. SMA spring is incorporated as the linear actuator of the motion stage. The three degrees of freedom motion of the end-effector is achieved based on a new type of SMA-driven PPR joint configuration to provide two translations and one rotational motion. The advantages of the SMA as an actuator is such as lightweight, higher accuracy, and micron-level movement to establish linear motion and silent actuation. The kinematic and jacobian relations are derived for the developed motion stage. The actuation of the SMA (Nitinol) spring actuator is accomplished by the use of a programmable power supply. In addition, the close loop PID control scheme to the SMA linear actuator is investigated. The mechanism has some inherent errors, as geometric errors (kinematic error), friction between the elements of the mechanism, etc, are significant issues in tracking the trajectory of the motion stage. Thus, to address the above issues, this study incorporates the dual-loop control scheme for better trajectory tracking and error compensation of the proposed motion stage. The control method employs a redundant feedback approach, in which discrete joint space displacements and mobile platform coordinates, and task space coordinates are determined as feedback signal using suitable sensors. In this control scheme, the actual joint displacement errors are computed using the redundant feedback data and corrected the desired joint displacement trajectory to obtain the desired task space trajectory. To measure the effectiveness of the used control scheme, a real-time prototype of the proposed motion stage (4- P PR) is developed and investigated the performance of the control method using some simple geometric trajectories. It is observed from the experiments that the motion stage using SMA linear actuation technique has good tracking performance using the control scheme. The developed motion stage can be implemented in the micro-stereolithography process and micron-level positioning application.

Experimental study on demountable CFST K-joints designed with blind bolts

Developing demountable structures that enable the replacement of damaged components and the reuse of intact parts in their extended service-life is an effective approach to reducing carbon emissions and prompt sustainable construction. This paper presents an experimental investigation on the behavior of novel demountable K-joints formed by concrete-filled steel tubular (CFST) chords and circular hollow sectional (CHS) braces connecting through blind bolts and curved endplates. A series of tests are conducted on the demountable K-joint specimens, where pined supports are applied at the ends of two braces whilst one end of the chord is under tension and the other is left free. Based on the tests, the failure mode, the ultimate capacity, the joint stiffness and the deformability of the demountable joints are investigated. After the initial loading, the damaged components are disassembled and replaced by new ones to form new joints which are then loaded again for the 2nd and 3rd service periods. It is found that the differences in joint ultimate capacity during multiple service periods are generally within 5%, testifying the effective reuse of the main structural components such as CFST chords and blind bolts. The effects of important parameters related to the demountability design, the joint configuration and the material strengths are evaluated through the tests. Finally, a simplified ultimate capacity prediction method for such demountable CFST K-joints is proposed and validated.

EFFECT OF WEIGHTBEARING AND FOOT POSITION ON 3D DISTAL TIBIOFIBULAR JOINT PARAMETERS

The aim of this study was to investigate the effect of different loading scenarios and foot positions on the configuration of the distal tibiofibular joint (DTFJ).Fourteen paired human cadaveric lower legs were mounted in a loading frame. Computed tomography scans were obtained in unloaded state (75 N) and single-leg loaded stand (700 N) of each specimen in five foot positions: neutral, 15° external rotation, 15° internal rotation, 20° dorsiflexion, and 20° plantarflexion. An automated three-dimensional measurement protocol was used to assess clear space (diastasis), translational angle (rotation), and vertical offset (fibular shortening) in each foot position and loading condition.Foot positions had a significant effect on the configuration of DTFJ. Largest effects were related to clear space increase by 0.46 mm (SD 0.21 mm) in loaded dorsal flexion and translation angle of 2.36° (SD 1.03°) in loaded external rotation, both versus loaded neutral position. Loading had no effect on clear space and vertical offset in any position. Translation angle was significantly influenced under loading by −0.81° (SD 0.69°) in internal rotation only.Foot positioning noticeably influences the measurement when evaluating the configuration of DTFJ. The influence of the weightbearing seems to have no relevant effect on native ankles in neutral position.

Joint Resource Allocation and Configuration Design for STAR-RIS-Enhanced Wireless-Powered MEC

In this paper, a novel concept called simultaneously transmitting and reflecting RIS (STAR-RIS) is introduced into the wireless-powered mobile edge computing (MEC) systems to improve the efficiency of energy transfer and task offloading. Compared with traditional reflecting-only RIS, STAR-RIS extends the half-space coverage to full-space coverage by simultaneously transmitting and reflecting incident signals, and also provides new degrees-of-freedom (DoFs) for manipulating signal propagation. We aim to maximize the total computation rate of all users, where the energy transfer time, transmit power and CPU frequencies of users, and the configuration design of STAR-RIS are jointly optimized. Considering the characteristics of STAR-RIS, three operating protocols, namely energy splitting (ES), mode switching (MS), and time splitting (TS) are studied, respectively. For the ES protocol, based on the penalty method, successive convex approximation (SCA), and the linear search method, an iterative algorithm is proposed to solve the formulated non-convex problem. Then, the proposed algorithm for ES protocol is extended to solve the MS and TS problems. Simulation results illustrate that the STAR-RIS outperforms traditional reflecting/transmitting-only RIS. More importantly, the TS protocol can achieve the largest computation rate among the three operating protocols of STAR-RIS.

Correlation between the spinopelvic type and morphological characteristics of lumbar facet joints in degenerative lumbar spondylolisthesis.

The correlation between the spinopelvic type and morphological characteristics of lumbar facet joints in patients with degenerative lumbar spondylolisthesis (DLS) was investigated. One hundred forty-two patients with L4 DLS were enrolled (DLS group), and 100 patients with lumbar disc herniation without DLS were selected as the control group (i.e., non-lumbar spondylolisthesis [NL] group). Morphological parameters of L4-5 facet joints and L4-5 disc height and angle were measured on 3D reconstructed CT images; namely, the facet joint angle (FJA), pedicle-facet joint angle (PFA), facet joint tropism, and facet joint osteoarthritis (OA). The L4 slip percentage, sacral slope, and lumbar lordosis were measured on radiographs. Patients in the DLS and NL groups were divided into 4 subgroups according to Roussouly classification (types I, II, III, and IV). In the DLS and NL groups, as the spinopelvic type changed from type II to type IV, the facet joint morphology showed a gradual sagittal orientation in the FJA, a gradual horizontal orientation in the PFA, a gradual severity in OA, and a gradual increase in the slip percentage, but changes were completely opposite from type I to type II. Additionally, compared with the NL group, the facet joint morphology in the DLS group had more horizontal orientation in PFA, more sagittal orientation in the FJA, and the facet joint tropism and OA were more severe. Facet joint morphology was correlated with spinopelvic type in the slip segment of DLS. Facet joint morphology was part of the joint configuration in different spinopelvic types, not just the result of joint remodeling after DLS. Moreover, morphological changes of the facet joints and DLS interacted with each other. Additionally, morphological remodeling of the facet joints in DLS played an important role in spinal balance and should be taken into consideration when designing a surgical approach.

Edge AI as a Service: Configurable Model Deployment and Delay-Energy Optimization With Result Quality Constraints

We propose a configurable model deployment architecture (CMDA) for edge AIaaS and present a flexible working mechanism by enabling the joint configuration of data quality ratios (DQRs) and model complexity ratios (MCRs) for the AI tasks. Along with commonly used resource allocation operations, the manager can improve the energy and delay performance of AI services with the desired quality of results (QoRs). We develop an energy-delay minimization problem under the framework of CMDA and propose a polynomial regression based relaxing method to solve the task configuration subproblem. We conduct experiments and simulations on the ImageNet classification and the common objects in context (COCO) object detection tasks using state-of-the-art deep learning models. We present the corresponding result quality tables (RQTs) and QoR regression models to illustrate the proposed method. The results of single task configuration and multi-task configuration and resource allocation on ImageNet classification and COCO object detection tasks demonstrate that the proposed method can achieve over 5× HDEC improvement compared with non-optimization schemes, and also show that joint configuration of DQR and MCR can achieve over 1.2× HDEC improvement compared with the methods that only configure DQR or MCR.

On the static failure behaviour of co-cured composite joints with enhanced interlaminar fracture energies via multiscale toughening

This paper is focused on the multiscale toughened co-cured composite interfaces of carbon/epoxy laminates using vacuum infusion and out-of-autoclave curing—with an emphasis on the role of enhanced interlaminar fracture energies on the static failure of laminate joints. To toughen co-cured interlaminar regions, three toughening routes are used: (i) epoxy matrix toughening with 10 wt% core–shell rubber (CSR) nanoparticles, (ii) 10 g/m2 polyphenylene sulfide (PPS) non-woven micro-fibre veil toughening, and (iii) multiscale toughening by combining epoxy matrix toughening with 10 wt% CSR nanoparticles and 10 g/m2 PPS veils. Double cantilever beam and end-notch flexure tests are conducted with the toughened interfaces for mode-I and mode-II fracture energies. Moreover, three co-cured joint configurations (viz. double-notch single lap, stepped scarf and skin-stiffener joints with the three toughening routes) are tested to characterise the role of enhanced interlaminar fracture energies on the static failure of laminate assemblies. The results show that the three toughening routes have significantly altered the R-curve behaviour and interlaminar fracture energies and that the degree of enhancement in mode-I and mode-II fracture energies is sensitive to the type of toughening route. Based on the material systems tested, the mode-I fracture initiation energy is enhanced by ∼150% with multiscale toughening, ∼65% with particle toughening, and ∼60% with veil toughening; whereas, the mode-II fracture initiation energy is enhanced by ∼85% with veil toughening and ∼35% with multiscale toughening—but reduced by ∼20% with particle toughening. The joint tests show that the toughening routes affect the static failure of the three joint configurations and that the strength and damage evolution of the co-cured joints depend on the interlaminar fracture energies. The strength of the co-cured single lap joints is increased by ∼50% with multiscale toughening and ∼40% with veil toughening; whereas, the strength of the co-cured skin-stiffener joints is enhanced by ∼35% with multiscale toughening and ∼45% with veil toughening. The failure mechanisms observed on the fracture surfaces indicate that the strength/failure behaviour of the co-cured joints depends on the dominant interlaminar fracture mode and the corresponding fracture energies. Overall, it is shown that the multiscale interlaminar toughening routes that are used to address the issue of delamination can also be effectively explored to enhance the static failure of co-cured laminate assemblies by toughening the co-cured interfaces/bondlines.

The investigation on dynamic damage evolution and energy absorption of FML pin joints with different ply stacking sequences

With fiber reinforced composites widely applied in aerospace, the crashworthiness aspects for aircraft have been an important part of the design. Fiber metal laminate (FML) is a kind of hybrid composite fabricated by fiber reinforced plastic composites and metal layers, showing a potential application on energy absorption. In this work, the damage evolution and energy absorption of FML pin joints are investigated comprehensively. The configurations of FML pin joints with constant geometric parameters are designed to avoid net-tension damage failure in the experiments. The damage evolution processes of specimens are captured by a high-speed camera, and the surface strain is calculated by Digital Image Correlation (DIC) method. Abaqus/Explicit solver is adopted to simulate the mechanical responses of FML pin joint considering ductile damage of metal, damage evolution of composites, and delamination of the interface. The results indicate that the initial dynamic ultimate bearing strength of FML incorporate notable contribution from inertia effects. The average bearing strength associated with energy absorption efficiency is related to the ply stacking sequence of composites. The fiber direction of laminates should be perpendicular to the movement direction of pin as much as possible under the premise that the initial ultimate bearing strength satisfies the design requirement. The results obtained in this work provide comprehensive design guidance for the improvement of crashworthiness in the composite fuselage.

On the Secure Performance of Intelligent Reflecting Surface-Assisted HARQ Systems

This paper analyzes the physical layer security performance of hybrid automatic repeat request (HARQ) systems with the assistance of an intelligent reflecting surface (IRS) and aims to reveal the primary factors that enhance PLS. First, closed-form expressions for the connection outage probability (COP) and secrecy outage probability (SOP) in HARQ with chase combining (HARQ-CC) are acquired using the generalized-K (KG) distribution. Then, these two critical metrics are derived while adopting HARQ with incremental redundancy (HARQ-IR), resorting to the mixture gamma (MG) distribution and the Mellin transform. Diversity and coding gain are also addressed through an asymptotic analysis of the COP and SOP. Finally, an evaluation of the numerical results demonstrates that a greater gain in the main channel and the wiretap channel can be produced by increasing the number of meta-surfaces rather than increasing the maximum transmission number, except for the higher signal-to-noise (SNR) region of HARQ-IR where the latter is preferred. This finding provides a significant guidance for the joint configuration of IRS and HARQ to achieve secure communication.

Energy Efficiency of a Wheeled Bio-Inspired Hexapod Walking Robot in Sloping Terrain

Multi-legged robots, such as hexapods, have great potential to navigate challenging terrain. However, their design and control are usually much more complex and energy-demanding compared to wheeled robots. This paper presents a wheeled six-legged robot with five degrees of freedom, that is able to move on a flat surface using wheels and switch to gait in rugged terrain, which reduces energy consumption. The novel joint configuration mimics the structure of insect limbs and allows our robot to overcome difficult terrain. The wheels reduce energy consumption when moving on flat terrain and the trochanter joint reduces energy consumption when moving on slopes, extending the operating time and range of the robot. The results of experiments on sloping terrain are presented. It was confirmed that the use of the trochanter joint can lead to a reduction in energy consumption when moving in sloping terrain.

Patient-specific femoral implant design using metamaterials for improving load transfer at proximal-lateral region of the femur

Loading configuration of hip joint creates resultant bending effect on femoral implants. So, the lateral side of femoral implant which is under tension retracts from peri‑implant bone due to positive Poisson's ratio. This retraction of implant leads to load shielding and gap opening in proximal-lateral region, thereby allowing entry of wear particle to implant-bone interface. Retraction of femoral implant can be avoided by introducing auxetic metamaterial to the retracting side. This allows the implant to push peri‑implant bone under tensile condition by virtue of their auxetic (negative Poisson's ratio) nature. To develop such implants, a patient-specific conventional solid implant was first designed based on computed-tomography scan of a patient's femur. Two types of metamaterials (2D: type-1) and (3D: type-2) were employed to design femoral meta-implants. Type-1 and type-2 meta-implants were fabricated using metallic 3D printing method and mechanical compression testing was conducted. Three finite element (FE) models of the femur implanted with solid implant, type-1 meta-implant and type-2 meta-implant were developed and analysed under compression loading. Significant correlation (R2=0.9821 and R2=0.9977) was found between the experimental and FE predicted strains of the two meta-implants. In proximal-lateral region of the femur, an increase of 7.1% and 44.1% von-Mises strain was observed when implanted with type-1 and type-2 meta-implant over the solid implant. In this region, bone remodelling analysis revealed 2.5% bone resorption in case of solid implant. While bone apposition of 0.5% and 7.7% was observed in case of type-1 and type-2 meta-implants, respectively. The results of this study indicates that concept of introduction of metamaterial to the lateral side of femoral implant can prove to provide higher osseointegration-friendly environment in the proximal-lateral region of femur.

Geometric and Material Modelling Aspects for Strength Prediction of Riveted Joints

The aim of this study is to develop a methodology for static strength and failure mode simulation of hot-driven riveted joints. The purpose is to be able to accurately estimate a rivet joint’s static strength behaviour and its failure mode without relying on experiments, to save both time and resources during the design of joints. The non-linear finite element analysis modelling framework considered the rivet joint configurations and geometry, the material properties of the plate and rivet as well as the clamping force of the hot-driven rivet. A ductile damage model was also implemented to capture the stress softening of the materials and the failure modes of the joints. Using experimental data from literature, the modelling framework is validated, and it is shown that it is able to capture the strength behaviour and failure modes of different configurations of rivet joints markedly well. The effect of the rivet pre-load on the mechanical response of the joint is also studied and it is shown that the strength of the joint increased with the increase in rivet pre-load. The modelling framework is then applied to an industrial component. The modelling framework is used to compare welding and riveting as joining methods in a component built in two grades of high-strength steel. It is found that the welded joint possessed greater strength compared to the proposed riveted joint. However, using the proposed simulation methodology developed, a riveted joint with matching strength to the welded joint could be designed.

A geometrical parameter study of the analytical stress calculation in adhesive joints with thick bonding layers

AbstractStrength and failure analyses are critical to the safe and sustainable design of any structure. In the case of adhesively bonded joints, particular attention must be paid to the adhesive layer, which is comparably compliant and subject to high stresses. Determining the stresses in the adhesive layer is essential to identify critical areas in the joint and prevent the formation of cracks. In most applications, bonded joints have thin adhesive layers that can already be accounted for with highly simplified analytical models. However, for the consideration of thicker adhesive layers, advanced models are required that take the adhesive layer into account in more detail.Therefore, in this work, an analytical model with a higher‐order displacement approach is presented to account for more complex deformation behavior in the adhesive layer. The applied advanced displacement approach is particularly suitable for joints with thicker adhesive layers. In addition, the model enables the calculation of stresses and strains in bonded joints for a wide range of joint configurations and applications. A parameter study is carried out to evaluate the effect of different thicknesses of the adhesive layer and to show the advantages of the current model compared to other existing ones. For verification, all analytical results were compared with corresponding Finite Element Analyses.

Enhancement on the low-pressure shot peened process of monotonic plastic deformation behaviors of Ni–4Cu–3Mo alloy/super austenite stainless steel dissimilar joints using laser beam welding

This research paper mainly discusses the low-pressure shot-peened (LPSP) process of 2 mm thick sheet plates of monotonic mechanical behaviors of Ni–4Cu–3Mo alloy/super austenite stainless steel (SASS) dissimilar materials joint by laser beam welding. Three types of butt joint (Sample-1, Sample-2, and Sample-3) configuration methods of the laser beam welding process were implemented at the Ni–4Cu–3Mo alloy/SASS dissimilar weldments and LPSP weldments. The microstructure image of the fusion zone revealed that the high heat inputs were distributed at the grain boundary and the prior coarse grain structures were converted into NiCr and C–Cr with significant improvement in the α'-martensite structure. To achieve continuous improvement in yield strength of LPSP weldments compared to the dissimilar weldments, the plastic deformations rate was decreased in the shot-peened weldments. The base metals of tensile samples length were prepared as ±5 mm; however, samples clearly indicated that the dissimilar weldments and LPSP weldments showed the failure in the fusion zone. The average elongation of dissimilar LPSP weldments was increased by 13%; however, the heat inputs collapsed the grain boundaries growth and the structure was converted into twin boundaries and α-martensite structures. The hardness measurement at the fusion zone of dissimilar and LPSP weldments was performed and the average hardness value of 290 HV at the fusion zone and 211 HV at the heat-affected zone was observed for LPSP weldments. The fracture morphology revealed that neither major cracks nor minor voids at the fusion zone of the tensile sample were formed.

Analysis of fracture toughness and fatigue crack growth rates of electron beam-welded dissimilar nickel-based superalloys: Mode-I cracks oriented normal to the weld

This paper discusses the experimentally obtained results of fracture toughness and fatigue crack growth rates of dissimilar metal-welded joints of Inconel 718 to Nimonic 80A. The dissimilar metal-welded joints were prepared in butt joint configuration using electron beam welding. Mode-I cracks were oriented normal to the weld. The base metals have different yield strength values (plastic mismatch) and ultimate tensile strength values but have the same elastic modulus and thermal expansion coefficients. The experiments were conducted using single-edge notched bend specimen design. The fracture toughness ( J) and fatigue crack growth rates of dissimilar metal-welded joints were affected by the direction of crack growth, such as cracks moving from stronger metal to weaker metal or vice versa. In comparison to Nimonic 80A (base metal), the J value of dissimilar metal-welded joint with crack direction from Nimonic 80A (stronger) to Inconel 718 (weaker) was lower. Moreover, the J value of dissimilar metal-welded joint was higher than that of Nimonic 80A (base metal) when crack traveled from Inconel 718 (weaker) to Nimonic 80A (stronger). In the fatigue crack growth rate test, the crack grew faster as it approached the weld interface from Nimonic 80A toward Inconel 718 due to crack acceleration. Conversely, the crack grew slowly in the opposite direction due to crack shielding. The onset of these effects began sooner for higher loads than lower loads.

Construction details affecting flanking transmission in cross laminated timber structures for multi-story housing

The desire of the building developers to leave the surfaces of cross laminated timber constructions in multi-story housings visible for the building user, leads to acoustic problems with the flanking sound transmission that cannot be controlled by means of wall linings. As a result, controlling flanking sound transmission by measures directly in the joint is getting increasingly important. The main parameter for describing the vibrational power transmission over a junction between structural elements is the vibration reduction index Kij. For this quantity, some planning values are spread over numerous publications. None of the currently available data sources represents a holistic view on the building acoustic performance of the on the market available products for elastic interlayers and fasteners which are used in a wall-ceiling junction. The following paper shows results of measurements of vibration reduction indexes of different configurations of a wall-ceiling joint in a test facility. Different elastic interlayers and fasteners were investigated. The vibration reduction indexes spread from 16db to 26dB as a function of the joint configuration and the load applied on the joint. The measurement results obtained are discussed and the essential parameters for influencing the flanking sound transmission are worked out and quantified.