Mechanical Fasteners Research Articles

Cracking Stopping in the Bondline of Adhesively Bonded Composite Adherents by Means of a Mechanical Fastener: Numerical and Experimental Investigation

Cracking Stopping in the Bondline of Adhesively Bonded Composite Adherents by Means of a Mechanical Fastener: Numerical and Experimental Investigation

Self-sensing time-domain reflectometry for detection of the bearing failure of a CFRP laminate fastener hole: effect of peeling of the insulator

Carbon-fiber-reinforced polymer (CFRP) composites are used in aerospace and automobile structures. For many CFRP structures, mechanical metallic fasteners are adopted. In internal structures such as a wing box, damage to CFRP structures around the fastener holes is difficult to see. A simple method of finding damage around fastener holes is thus required for CFRP structures. This study applies self-sensing time-domain reflectometry to detect bearing failure around fastener holes of CFRP structures. In a previous paper, the effect of fasteners was minimized when the micro-strip line (MSL) was placed apart from the fasteners. This study numerically and experimentally investigates the peeling of glass-fiber-reinforced polymer (GFRP) insulator. A bearing failure results in embossing at the edge of a fastener hole. The embossing produces a wedge that causes the peeling of GFRP, generating a gap between the GFRP and CFRP. The gap strongly affects the characteristic impedance of the MSL.

Effect of Elevated Temperatures on the Mechanical Performance of Pultruded FRP Joints with a Single Ordinary or Blind Bolt

Presented in this paper is a combined experimental and analytical modeling study of the strength of pultruded fiber-reinforced polymer (FRP) single-bolted double-lap joints subjected to tensile loading and elevated temperatures. Dynamic mechanical analysis (DMA) and thermogravimetric analysis (TGA) are conducted on the polymeric composite material to determine the glass transition temperature and decomposition temperature, respectively. Based on the DMA and TGA results, and to cover glass transition without any material decomposition, the six temperatures selected for the test program are +23+23, +60+60, +100+100, +140+140, +180+180, and +220°C+220°C. Three nominally identical joints are tensioned to failure at each temperature. A total of 36 double-lap joints are tested, comprising 18 joints fabricated with ordinary steel bolting and the other 18 with novel blind bolting. A comparison is made based on load-displacement curves, failure modes, and maximum (ultimate) loads. It is found that both methods of mechanical fastening experience a reduction of 85% in maximum load as the test temperature increases from +23+23 to +220°C+220°C. Three proposed empirical or mechanism-based models for characterizing strength under elevated temperatures are shown to provide good predictions for the maximum loads obtained in the test program.

Evaluation of Corrosion Performance of Zinc-Plated Underhood Automotive Fasteners Using Salt Spray Test

Mechanical fasteners such as screws, nuts, bolts, and washers are integral components in a vehicle. Rust or corrosion mechanisms of fasteners in the automotive industry is complex and may probably due to many factors includes temperature, pH, ion concentrations, coatings compositions as well as fastener geometry. Most of underhood fasteners used by PROTON models are Zinc coated fasteners. PROTON requires interior fasteners are coated to a minimum of 5 μm, while exterior fasteners are of 8 μm minimum thickness. There is a need to understand the corrosion performance of such fasteners in order to improve cosmetic and functional performances of these fasteners. The main objective of this study is to evaluate corrosion performance of three different compositions of Zinc-coated underhood fasteners using laboratory test. Samples were subjected to salt spray test with 5% NaCl for specific periods of time, in accordance ASTM B117-90 and JIS Z 2371:2000 conforming to their corrosion resistance requirements based on coating type and thickness. Results of the study revealed that Zn-Ni and Zinc-flake platings exhibit superior corrosion resistance characteristics with rating number (RN) of 10 compared to conventional 8 μm hexavalent-chrome free plated fasteners.

Experimental analysis of single-lap composite joints with two different adhesives at various conditions

Composite materials have been used in the transport industry in the recent years. The assembly of composite materials has been performed with either adhesive joints or other mechanical fasteners. Adhesive joints are more preferred because of their easy usages, lightness and the stress concentration, which is very important in the design, occurs less than the other type joints. In this study, load-carrying capacity of single-lap joints bonded with different adhesives was found, experimentally. Woven glass fibre–epoxy composites manufactured by using vacuum assisted resin infusion method (VARIM) were used as adherends. FM73 epoxy film adhesive and DP-460 paste adhesive were used as adhesive materials. Several loading conditions, 5, 10 and 15 J, that possibly happen in the operation life were considered. The tests were carried out room temperature (25℃), 50℃ and 80℃. From the results, it is observed that the load-carrying capacity of single-lap joints significantly varies with adhesive types and temperature.

Extensive characterisation of advanced manufacturing solutions for the ITER Central Solenoid pre-compression system

The ITER Central Solenoid (CS), positioned in the center of the ITER tokamak, will provide a magnetic field, contributing to the confinement of the plasma. The 13m high CS consists of a vertical stack of 6 independently driven modules, dynamically activated. Resulting opposing currents can lead to high separation forces. A pre-compression structure is implemented to counteract these opposing forces, by realising a continuous 180 MN coil-to-coil contact loading. Preload is applied by mechanical fastening via 9 subunits, positioned along the coil stack, each consisting of 2 outer and 1 inner tie plate. The tie plates therefore need to feature outstanding mechanical behaviour in a large temperature range. High strength, Nitronic®-50 type F XM-19 austenitic stainless steel is selected as candidate material. The linearised stress distribution reaches approximately 250MPa, leading to a required yield strength of 380MPa at room temperature. Two different manufacturing methods are being studied for the procurement of these 15m long tie plates. A welded solution originates from individual head- and slab-forgings, welded together by Gas Metal Arc Welding (GMAW). In parallel, a single piece forged solution is proven feasible, impressively forged in one piece by applying successive open die forging steps, followed by final machining. Maximum internal stress is experienced during cool-down to 4K as a result of a large difference in thermal contraction between the support system and the coils. Furthermore, the varying magnetic fields in the independently driven coils introduce cyclic loading. Therefore, assessment of the two manufacturing solutions, in terms of both static and dynamic mechanical behaviour, is performed at ambient as well as cryogenic temperature. An extensive characterisation including microstructural and mechanical examination is conducted, evaluating the comparative performance of both solutions, reporting, amongst others, yield strength reaching the requirement for both solutions.

Failure modes and reinforcement techniques for timber beams – State of the art

Highly loaded and large span timber beams are often used for halls, public buildings or bridges. Reinforcement of beams may be required to extend the life of the structure, due to deterioration or damage to the material/product or change of use. The paper summarises methods to repair or enhance the structural performance of timber beams. The main materials/products cross sections and geometries used for timber beam are presented. Furthermore, their general failure modes are described and typical retrofitting and reinforcement techniques are given. The techniques include wood to wood replacements, use of mechanical fasteners and additional strengthening materials/products.

Connection Performance for LVL-Concrete Composite Floor System

The LVL-concrete composite (LCC) structure is a hybrid in system which the LVL member is well connected to the concrete slab by a connector to produce composite action. Various types of connector with different stiffness and shear capacity are available in the market currently. The stiffness of the connector is identified through the push-out experiment. The notch connections for LVL concrete composite beams have higher stiffness and strength compared to mechanical fasteners. This paper discusses the experimental results of symmetrical push-out tests on 3 different types of connector, 150mm rectangular notch with 10mm diameter screw, 100mm rectangular notch with 8mm diameter screw and 100mm triangular notch with 8mm diameter screw. The experimental test was shear push out to failure and the type of failure was discussed. The 150mm rectangular notch was found to be strongest among all and low cost. The 100mm rectangular notch was found to be slightly stiffer than 100mm triangular notch but 100mm triangular notch is easier to construct with only 2 cut. The maximum strength and stiffness at ultimate limit states and serviceability limit states of each type of connection were discussed in this paper.

차체 소재 다변화에 따른 체결 및 접합기술

Abstract The ultimate goal of developing body is revealed the “lightweight” at latest EuroCarBody conference 2012 and the most core technology is joining process to make lightweight car body design. Accordingly, in this study, the car body assembly line for the assembly process applies to any introduction, particularly in the assembly of aluminum alloy and composite materials applied by the process for the introductory approached. Process were largely classified by welding (laser, arc, resistance, and friction stir welding), bonding (epoxy bonding) and mechanical fastening (FDS, SPR, Bolting and clinching). Applications for each process issues in the case and the applicable award was presented, based on the absolute strength of the test specimens and joining characteristics for comparative analysis were summarized. Finally, through this paper, we would tried to establish the characteristics of the joint for lightweight structure.Key Words : Lightweight, Joining technology, Mechanical fastening, Adhesive bonding, Euro car body, Tensile shear strengthISSN 1225-6153Online ISSN 2287-8955

Short-time procedure for fatigue assessment of beech wood and adhesively bonded beech wood joints

Timber as a structural material has experienced a revival for aspects related to sustainability, positive effect on interior building and increased architectural possibilities. To overcome a series of limitations related to partly obsolete traditional techniques, timber engineering sets high expectations on adhesive bonding as a joining method. Research on adhesively bonded timber joints has proven their superiority over mechanical fasteners in terms of strength and stiffness. Research on methods to design adhesively bonded timber joints under static loads is currently ongoing and significant progress has already been achieved. The topic of fatigue behaviour, however, has only been addressed very rarely, largely because “classical” methods for fatigue assessment based on Woehler curves, is extremely time-consuming. This paper aims to fill this gap by describing and validating an advanced time- and cost-efficient approach to quantify the behaviour of bonded timber joints under fatigue. Therefore the fatigue behaviour of beech wood as base material and adhesively bonded beech wood joints as structural elements were investigated by means of a short-time procedure. In this approach, cyclic tests with a stepwise increase of the stress amplitude were performed while the plastic strain amplitude was measured. The plastic strain amplitude gives reliable signals for an estimation of the fatigue strength. This is validated by traditional cyclic tests with constant stress amplitudes. It could be shown that the testing approach provides reliable results and has a high potential in time and cost savings for wood and adhesively bonded wood joints.

Intelligent Thermal Control of Resistance Welding of Fiberglass Laminates for Automated Manufacturing

A novel approach to automate large-scale resistance welding of thermoplastic composite materials, based on real-time temperature control, is presented in this paper. Resistance welding, a kind of fusion bonding, is a widespread alternative process to mechanical fastening and adhesive bonding in joining thermoplastic composites. A second-order linear observer was identified to estimate the online temperature at the weld interface. A fuzzy logic controller (FLC) was designed to control the weld temperature using both process voltage and linear weld speed as the control inputs and using the temperature estimate as the feedback signal. The FLC was implemented in real time with the experimental setup using an industrial robot—KUKA KR 210. The closed-loop controller was capable of successfully controlling the weld temperature within 10% of the desired temperature, resulting in superior weld quality when compared to open-loop results. The results thus affirm the suitability of the control strategy for large-scale automated welding.

Pullout Performance of Common Construction Fasteners from Long Fiber Thermoplastic Composites

The recent increase in cyclone activity in the last 20 years has pressured the construction industry to look for alternative materials for roof construction. Although plywood is a cheap material, its mechanical properties are highly dependent on moisture content. Long fiber thermoplastics are an emerging type of plastic materials that feature enhanced mechanical properties due to high aspect ratio discontinuous fibers in a tough polymer matrix. The present study focuses on comparing the pullout strength of commonplace fasteners from plywood and long fiber thermoplastic composite panels. Specimens were tested according to ASTM standards D1761-88 and D6117-97 for mechanical fasteners in wood and long fiber thermoplastic (LFT) composites. Common construction nails like 6D, 10D and 16D and a #8 screw were used to compare the performance in terms of withdrawal. The data showed that LFT composites had withdrawal strength on average two to three times that of plywood for all tested fasteners types. Experimental data was analytically verified by APA TT-109 guidelines.

On the analysis of force during secondary processing of natural fiber‐reinforced composite laminates

The rising concern regarding global warming has ignited a quest in the research fraternity towards development of sustainable materials that can reduce the carbon footprint. Natural fiber reinforced composites have made an excellent impression in the area of sustainable development because of their environmental and ecological aspects. These materials are widely used for manufacturing of engineering products. But, the use of natural fiber composites for engineering applications necessitates making of holes in order to ascertain assembly of several components by means of mechanical fastening. In this research endeavor, the drilling behavior of nettle/polypropylene (PP) composites has been experimentally investigated. The relative significance of the input process variables has also been studied with the help of statistical technique called analysis of variance (ANOVA). The present study established few significant facts in context of drilling of natural fiber reinforced composites. It has been observed that the facts established for drilling of synthetic fiber reinforced thermoset composites cannot be directly applied for natural fiber reinforced composites. POLYM. COMPOS., 38:164–174, 2017. © 2015 Society of Plastics Engineers

The Effect of Interlayer on the Structural Behavior of Timber Concrete Composite Utilizing Self-Compacting and Conventional Concretes

TCC consists of timber and concrete members acting compositely together. The strength, stiffness, location and number of connectors play a crucial role for the composite action and structural performance of TCCs. In upgrading of timber floor to TCC, existing floorboards can be used as a permanent formwork whilst the concrete is then poured over connectors inserted into timber floorboards. Hence, the influence of interlayer on mechanical properties of TCC joints and floor is of interest. To date, conventional concrete has been used in most investigations on TCCs. Self-compacting concrete (SCC) is recognized as a highly workable which is compacted without use of conventional vibration methods. As such, there is a potential for application of SCC in TCCs where the pumping, and compacting of conventional concrete poses a challenge e.g. difficult to access areas in the renovation of timber floors in multi-story buildings. This paper focuses on utilizing mechanical fasteners for their ductility and stiffness to connect a SCC slab (with and without interlayer) to a timber beam, that is, the use of SCC forms an important parameter of this research. The experiment consists of push-out tests to characterizeload capacity and various stiffness. The responses of the specimens are also compared to that of TCCs with conventional concrete.

Process modeling, joint virtual testing and construction of joint connectors for mechanical fastening by flow-drilling screws

In this work, a computational approach is proposed in order to help establish the effect of various flow-drilling screw process and material parameters on the quality and the mechanical performance of the resulting flow-drilling screw joints. Toward that end, a sequence of three distinct computational analyses is developed. These analyses include the following: (a) finite element modeling and simulations of the flow-drilling screw process; (b) determination of the mechanical properties of the resulting flow-drilling screw joints through the use of three-dimensional, continuum finite element–based numerical simulations of various mechanical tests performed on the flow-drilling screw joints and (c) determination, parameterization and validation of the constitutive relations for the simplified flow-drilling screw connectors, using the results obtained in (b) and the available experimental results. The availability of such connectors is mandatory in large-scale computational analyses of whole-vehicle crash or even in simulations of vehicle component manufacturing, for example, car-body electro-coat paint-baking process. In such simulations, explicit three-dimensional representation of all flow-drilling screw joints is associated with a prohibitive computational cost. The approach developed in this work can be used, within an engineering-optimization procedure, to adjust the flow-drilling screw process and material parameters (design variables) in order to obtain a desired combination of the flow-drilling screw joint mechanical properties (objective function).

Effect of laser shock peening and cold expansion on fatigue performance of open hole samples

Mechanical fastening is still one of the main methods used for joining components. Different techniques have been applied to reduce the effect of stress concentration of notches like fastener holes. In this work we evaluate the feasibility of combining laser shock peening (LSP) and cold expansion to improve fatigue crack initiation and propagation of open hole specimens made of 6061-T6 aluminum alloy. LSP is a new and competitive technique for strengthening metals, and like cold expansion, induces a compressive residual stress field that improves fatigue, wear and corrosion resistance. For LSP treatment, a Q-switched Nd:YAG laser with infrared radiation was used. Residual stress distribution as a function of depth was determined by the contour method. Compact tension specimens with a hole at the notch tip were subjected to LSP process and cold expansion and then tested under cyclic loading with R=0.1 generating fatigue cracks on the hole surface. Fatigue crack initiation and growth is analyzed and associated with the residual stress distribution generated by both treatments. It is observed that both methods are complementary; cold expansion increases fatigue crack initiation life, while LSP reduces fatigue crack growth rate.

Enhancement of shear transfer in composite deck with mechanical fasteners

Reinforced concrete construction and steel construction are two of the most common contemporary construction methods. Both methods make use of composite decks as floor systems and diaphragms. During the design of composite decks, the interaction between the steel deck and concrete slab is typically disregarded when calculating the strength of the composite diaphragm due to lack of complete shear transfer, as existing practices such as stamping are not effective to provide substantial composite action. This conservative assumption essentially results in non-efficient use of material. This paper presents a method for ensuring shear transfer through the use of conventional sheet metal screws, driven through the corrugated steel deck and embedded in the fresh concrete. This method is proposed for use in the field between formed steel beams. Both experimental and analytical studies support an increase in strength with the addition of embedded fasteners. Further, experimental results indicate an additional increase in strength with the addition of synthetic reinforcing fibers. The increase in strength with the addition of the fasteners is on the order of 100%. When fasteners are already in use, the addition of synthetic reinforcing fibers can increase strength on the order of 10%. The ultimate deflection of enhanced deck is comparable to deck tested without fasteners, but the initial stiffness of enhanced deck is much higher.

Self-Sensing TDR for Bearing Failure Detection of CFRP Laminate Fastener Hole with Particular Reference to the Effect of Fasteners

Carbon fiber reinforced polymer composites (CFRP) have been applied to aerospace and automobile structures. For many CFRP structures, mechanical metallic fasteners are usually adopted. For the fasteners used in internal structures such as a wing box, the damage to the CFRP structures around fastener holes is visually quite difficult to find. A simple method to find the damage around fastener holes is required. In this study a self-sensing time domain reflectometry (TDR) method is newly applied to detect bearing failure around the fastener holes of CFRP structures. A microstrip-line method is generally used to create a transmission line. When the transmission line is mounted near the metallic fasteners, they may affect the impedance of the transmission line. In this study, the effect of distance between the fasteners and the transmission line was numerically investigated using a finite difference time domain analysis method. After finding the appropriate distance, experiments were performed to detect the bearing failure around a fastener hole. The experiments showed the performance of the self-sensing TDR for detecting bearing failure.

Adhesive thickness effects of a ductile adhesive by optical measurement techniques

Adhesive bonding is an excellent alternative to traditional joining techniques such as welding, mechanical fastening or riveting. However, there are many factors that have to be accounted for during joint design to accurately predict the joint strength. One of these is the adhesive layer thickness (tA). Most of the results are for epoxy structural adhesives, tailored to perform best with small values of tA, and these show that the lap joint strength decreases with increase of tA (the optimum joint strength is usually obtained with tA values between 0.1 and 0.2mm). Recently, polyurethane adhesives were made available in the market, designed to perform with larger tA values, and whose fracture behaviour is still not studied. In this work, the effect of tA on the tensile fracture toughness (Gnc) of a bonded joint is studied, considering a novel high strength and ductile polyurethane adhesive for the automotive industry. This work consists on the fracture characterization of the bond by a conventional and the J-integral techniques, which accurately account for root rotation effects. An optical measurement method is used for the evaluation of crack tip opening (δn) and adherends rotation at the crack tip (θo) during the test, supported by a Matlab® sub-routine for the automated extraction of these parameters. As output of this work, fracture data is provided in traction for the selected adhesive, enabling the subsequent strength prediction of bonded joints.

Static and fatigue testing thin riveted, bonded and hybrid carbon fiber double lap joints used in aircraft structures

The static strength and fatigue resistance of mechanically fastened, bonded and hybrid double lap joints using relatively thin carbon fiber adherends have been experimentally investigated. The aim was to compare the static strength and fatigue resistance of a hybrid joint configuration consisting of both bonding and riveting, a purely riveted joint and a purely bonded joint. The effect of changing various parameters such as the mechanical fastener array configuration, rivet clamping pressure, bond strength, initial defects and curing conditions were also investigated.No significant difference in the static strength of the bonded joints and hybrid joints was observed. However, the investigation showed that the fatigue resistance of a hybrid joint is superior to that of a bonded joint, particularly in the case where defects are present in the adhesive bondline; such defects may include cracking or an improperly cured bondline that would significantly reduce joint static strength and fatigue life.The damage mechanism and failure mode in these three different joint configurations varied, ranging from bearing failure of the riveted joints through to tension failure in the hybrid joints. These were found to be controlled by the various parameters such as adhesive bond strength, clamping pressure and adherend bearing strength.