Mechanical Fasteners Research Articles

Enhanced Mechanical Joining between Carbon-Fiber- Reinforced Plastic and Steel Plates Using the Clearance-Filling Effect of Structural Adhesive

When carbon-fiber-reinforced plastic (CFRP) and steel are joined using blind riveting and bolting, fastener inclination occurs due to the clearance between the fastener and hole. To this end, this study investigated the unavoidable occurrence of clearance when joining metal and composite materials using mechanical fastening. The effect of inclination on the lap shear strength (LSS) was quantitatively investigated under various conditions. In riveting, breakage occurred mainly in the rivet; the LSS between the CFRP and steel improved by approximately 33% when the clearance was filled with structural adhesive compared to that in the unfilled state. In bolting, a washer was essential since it not only reduced the force exerted on the bolt but also reduced the bending deformation of the steel plate where breakage occurred. The clearance-filling effect showed the same effect as using a washer even without using it. In addition, the LSS was improved by approximately 10% by filling the clearance with a structural adhesive in the case of bolting with washers. Additionally, the force distribution for the fastening segment was calculated under the application of an external force, and the results demonstrated that hybrid-bonded fastening using a clearance-filling during mechanical bonding is essential for strong fastening.

A parametric study of insertion and retention forces in cantilever hook

Adhesive bonding, mechanical fastening, and snap-fit are all ways for attaching plastic components together. Snap-fit is employed to assemble plastic parts because it is an efficient, cost-effective, and fast joining technique. When it comes to snap-fits, you have two options: separable and inseparable. The term separable refers to the ability of the components to be dismantled successfully without breaking, whereas inseparable refers to the plastic parts being permanently attached. This investigation focuses on cantilever snap-fit since it is frequently used in the automotive, aerospace, and other sectors. Numerous aspects and parameters affect the functioning of snap-fits, notably on the forces of the insertion and retention. The parameters are the feature thickness (Tb), beam length (Lb), beam width (Wb), base radius (Rb), mounting (α) and dismounting angle (β). The forces required to attach and detach the snap-fits are thought to increase as the insertion and retention angles increase. The results can be seen that higher insertion and retention angle contributes to higher insertion and retention forces as portrayed from Set 7 with the value of 1.1052 N and -1.0214 N.

Composite Beams Made of Waste Wood-Particle Boards, Fastened to Solid Timber Frame by Dowel-Type Fasteners

To increase the sustainability of prefabricated timber buildings and constructions, composite timber beams with "box" cross-sections were developed in collaboration with an industry partner. They were constructed from a solid timber frame and from webs made of residual waste wood-particle boards from prefabricated timber buildings production. The developed beams' design concepts presented in this paper were governed by architectural features of prefabricated timber buildings, geometrical limitations, available production technology, and structural demand related to various possible applications. The paper presents the results of experimental bending tests of six variations of the developed composite timber beams constructed by mechanical fasteners only. The developed design concept of composite timber beams without adhesives is beneficial compared to glued beams in terms of design for deconstruction and lower VOC emissions. The tests were conducted to study the influence of the following parameters on the beams' mechanical behavior: (i) web material (oriented strand boards (OSBs) vs. cement-particle boards); (ii) the influence of beam timber frame design (flanges and web stiffeners vs. flanges, web stiffeners, and compressive diagonals), and (iii) the influence of stiffener-flange joint design. Besides the beams' load-bearing capacities, their linear and non-linear stiffness characteristics were the main research interest. While adding compressive timber diagonals did not prove to significantly increase the stiffness of the beams in the case of cement-particle board webs, it increased their load-bearing capacity by enabling the failure of flanges instead of prior webs and stiffener-flange joints failure. For beams with OSB webs, failure of the bottom flange was achieved already with the "basic" timber frame design, but timber diagonals proved beneficial to increase the stiffness characteristics. Finally, mechanical characteristics of the developed beams needed in structural design for their application are provided together with further development guidelines.

Experimental and numerical evaluation of pultruded GFRP double-lap joints with different mechanical fasteners

Evaluating the structural behavior of connections is of core importance in the design of a Pultruded Glass Fiber Reinforced Polymer (PGFRP) structure. In this paper PGFRP double lap-joint specimens mechanically fastened by Through-Bolts (TB) and Hollo-Bolts (HB) were tested under uniaxial tension test in static conditions. A three-dimensional progressive Finite Element (FE) model was proposed and validated to simulate joint failure. A parametric study was conducted to investigate the influence of edge distance-to-hole diameter (e/d), number of bolts (single, double, and triple bolts), bolt diameter, width-to-hole diameter (w/d), and thickness. The model agreed well with the experimental results regarding load vs displacement, load vs strain and failure characteristics. From the result analysis, it was found that connection resistance increased with an increase in the number of bolt rows. Hence the triple HB connection with specimen ID T12H4 demonstrated an overall ultimate failure load of 57.75 kN. While the aforementioned values were approximately 26% higher when compared to TB for the same configuration.

Studies on Metallic Glasses in Utsunomiya University

Studies on dissimilar metal welding and mechanical fastening using metallic glasses in Utsunomiya University have been introduced. Metallic glass ribbons placed between the two dissimilar metal plates become supercooled liquid with low viscosity by resistance welding and promote supercooling at the nuggets. As a consequence, the residual stress at the welding boundary and the formation of brittle intermetallic compounds are suppressed, resulting in excellent dissimilar resistance welding with high joint strength and high reproducibility. Mechanical fastening of two metal plates is also demonstrated by resistance heating and viscous flow forming of metallic glass rivets. Producing metallic glass rivets using bulk metallic glasses by a resistance heating is now under examination.

Bonded connections of pultruded sections for floor system studied using digital image correlation

An experimental investigation of bonded connections of Fiber Reinforced Polymer (FRP) pultruded sections for a new floor design is presented. Flat plates with T-up ribs are bonded to the lower flanges of I-beams and used as a structural form for the concrete floor. Adhesively bonded connections with or without mechanical fasteners of different types and configurations were examined through 48 bond specimens tested in tension. Digital Image Correlation (DIC) was used to capture strain and slip profiles along the connection interface, from which shear and peeling stress distributions were established. The study showed that connections reached 80–100% of the full capacity of the member, governed by the transverse strength of the I-beam. Most samples experienced mixed failure modes. The two highest occurrences were fiber-tear of the ribbed plate, where longitudinal fibers appeared on both surfaces, and adhesive failure, where epoxy appeared on one surface only in certain parts. Using fasteners with the adhesive increased the ultimate capacity by up to 19%. Embedment of fasteners inside the concrete had little effect on ultimate strength. A method was developed to convert DIC measured strains into peeling and shear stresses. The combined test data was used to establish the shear-peeling stress failure envelope, which agreed very well with the theoretical interaction expression. A bond-slip relationship was also deduced from the DIC test results.

Secondary bonding of CF/PEKK thermoplastic composites with a PEI film adhesive in a press welding process

High-performance poly-ether-ketone-ketone (PEKK) thermoplastic (TP) composites, which are beginning to gain interest in the aerospace industry, require a joining procedure to integrate the individual parts. Amorphous TP bonding has been recently proposed to address the limitations of commonly used joining techniques for composites, such as mechanical fastening and adhesive bonding. In this study, we investigated the adhesive properties of a polyetherimide (PEI) film applied by hot press welding as an amorphous polymer interlayer of PEKK laminate. The temperature range of the bonding process was determined via differential scanning calorimetry analysis. The bonding strength was evaluated through single-lap shear tests. The effect of process temperature on the bonding strength was qualitatively analyzed via fracture surface morphology analysis. The interface between PEKK and PEI was analyzed via optical microscopy. The adhesive strength was as low as about 5 MPa up to the bonding temperature of 280[Formula: see text]C but then started to improve as the temperature increased, which is attributed to the interdiffusion of the PEKK matrix and PEI adhesive film. The maximum bonding strength of 23 MPa was confirmed at a bonding temperature of 340[Formula: see text]C. A mixed failure mode consisting of a relatively high ratio of fiber-tear failure to light-fiber-tear failure is observed at this process temperature. This failure mode can be attributed to the bonding temperature condition at which PEKK begins to melt.

К ПОВЫШЕНИЮ НАДЕЖНОСТИ СЕЛЬСКОХОЗЯЙСТВЕННЫХ ПРИЦЕПОВ

A method for improving the reliability of agricultural trailers by replacing steel sides with composite sandwich structures is considered, which makes it possible to reduce their weight with a general improvement in performance. The fastening of such boards to the metal frame of the platform is carried out using steel supports. Carrying out loading and unloading operations can be carried out by overturning the side board around the lower hinged supports, with the opening of the latches on the two upper supports. A comparative analysis of the existing methods of joining "steel-composite" (adhesive, with the help of mechanical fasteners, combined, glue-pin) made it possible to identify their shortcomings when using a multilayer composite structure characterized by insufficient strength of the inner layers adjacent to the support. The design of the lower hinged support, devoid of the described shortcomings, has been developed. The connection is carried out using two steel lugs containing profiles with spearshaped fasteners, which are introduced into the skin prepregs at the stage of composite manufacturing. The lugs are tightened with bolts, which allows you to create a reliable connection between the steel hinged supports and the side plate, which consists of a multilayer composite. A method for calculating the lower support has been developed, as a result of which the most loaded fasteners have been identified, and an expression has been obtained to determine the maximum acting force. Recommendations are proposed for calculating the strength of the most loaded fastener according to the allowable shear stresses of its cylindrical part.

Static and Fatigue Strength and Failure Mechanisms of Riveted Lap Joints of CFRP Composites

The background of this work is the search for the most effective ways of joining composites, inter alia in aeronautical applications. The purpose of this study was to analyze the impact of mechanical fastener types on the static strength of lap joints of composite elements and the impact of fasteners on the mechanism of failure of such joints under fatigue load. The second objective was to check to what extent the hybridization of such joints, consisting of supplementing them with an adhesive joint, affects their strength and the mechanism of failure of such joints loaded with fatigue. Damage to composite joints was observed using computed tomography technology. The fasteners used in this study (aluminum rivets, Hi-lok and Jo-Bolt) differed not only in terms of the materials they were made of, but also in terms of the pressure forces they exerted on the joined parts. Finally, in order to check how a partially cracked adhesive joint affects the load on the fasteners, numerical calculations were carried out. Analyzing the results of the research, it was found that partial damage to the adhesive joint of the hybrid joint does not increase the load on the rivets and does not impair the fatigue life of the joint. An important advantage of hybrid joint is the two-stage destruction of the connection, which significantly increases the safety of aircraft structures and facilitates the process of supervising their technical condition.

A Laser Shock-Based Disassembly Process for Adhesively Bonded Ti/CFRP Parts

The application of adhesively bonded joints in aerospace structural parts has increased significantly in recent years and the general advantages of their use are well-documented. One of the disadvantages of adhesive bonding is the relevant permanence, when compared to traditional mechanical fastening. End-of-life processes generally require the separation of the adherents for repair or recycling, and usually to achieve this, they combine large mechanical forces with a high temperature, thus damaging the adherents, while consuming large amounts of energy. In this work, a novel disassembly technique based on laser-induced shock waves is proposed for the disassembly of multi-material adhesively bonded structures. The laser shock technique can generate high tensile stresses that are able to break a joint, while being localized enough to avoid damaging the involved adherents. The process is applied to specimens made from a 3D-woven CFRP core bonded to a thin Ti layer, which is a common assembly used in state-of-the-art aircraft fan blades. The experimental process has been progressively developed. First, a single-sided shot is applied, while the particle velocity is measured at the back face of the material. This method proves ineffective for damage creation and led to a symmetric laser configuration, so that the tensile stress can be controlled and focused on the bond line. The symmetric approach is proved capable of generating a debonding between the Ti and the CFRP and propagating it by moving the laser spot. Qualitative assessment of the damage that is created during the symmetric experimental process indicates that the laser shock technique can be used as a material separation method.

Interlaminar mechanical performance of latent-cure epoxy joints

Because of uncertainty in bond strength of adhesively bonded composite structures for air flight, redundant load paths, such as mechanical fasteners or other crack arresting features, are required for certification. However, these redundant load paths add extra weight to the structure, induce significantly greater fabrication time and cost, and introduce local stress concentrations (in the case of mechanical fasteners) from which damage can more readily initiate. Structures with co-cured joints are more predictable, require much fewer redundant load paths, and are therefore more desirable. A secondary bonding technique for polymer-matrix composites that aims to produce co-cure-like joints with a continuous interface is briefly presented. A brief progression of mechanical testing results is reported and compared to actual co-cured joint performance. The purpose of the work is to determine the feasibility of this technology to produce a secondary bond equivalent in performance and predictability to that of a co-cured material. Joint performance was measured using six ASTM standard tests to measure interlaminar tensile and shear strength as well as mode-I and mode-II interlaminar fracture toughness at ambient temperature. After 50 process iterations, the final overall average joint performance exceeded 80% of the co-cured performance and in some tests had outperformed the co-cured specimens. The results suggest a high degree of feasibility of the technology to be pursued for future development with the intent to increase performance as well as reliability.

Joining of Aluminum Alloy AA7075 and Titanium Alloy Ti-6Al-4V through a Friction Stir Welding-Based Process

Combining dissimilar parts has become imperative for developing the structures based on lightweight materials, such as metal alloys, polymers or polymer matrix composites, and this has become one of the solutions to reverse the current trend of CO2 emissions in the transport sector. However, given the usual property disparities, joining dissimilar materials in multi-material and multi-purpose structures raises new engineering challenges. Advanced joining processes, such as friction stir welding (FSW), have emerged and have been applied across several sectors as a promising alternative to conventional joining processes, such as mechanical fastening or adhesive bonding. In the present work, and in order to avoid the development of intermetallic compounds (IMCs), a different approach from the conventional technique of friction stir welding was applied to the production of dissimilar overlapping joints. These dissimilar joints were fabricated using a high strength aluminum alloy (AA7075-T651) and a titanium alloy (Ti-6Al-4V), both materials widely used in automotive, aeronautics and space industries. To perform a systematic investigation, the Taguchi method was used to determine the process parameter combinations to enable the fabrication of this type of dissimilar joints. The joints were subjected to quasi-static tensile shear tests to assess their mechanical performance and were compared to conventionally riveted joints in different configurations, namely, single and double connection points. The joints produced by the FSW based method showed higher mechanical performance. To assess the local properties, some of the fractured regions of the joints were subjected to hardness assessments, revealing no significant change in the hardness in the tested areas. Finally, a statistical study was performed to analyze the main effects and interactions of the process parameters, to identify their influences on the mechanical performance of the joints.

Modeling of a concrete floor incorporating GFRP Stay-in-Place structural form

A novel concrete floor design, featuring embedded glass fiber-reinforced polymer (GFRP) stay-in-place (SIP) forms adhesively bonded to the bottom flanges of GFRP I-beams has been developed. The paper presents a comprehensive finite element analysis (FEA) of this system with emphasis on the two orthogonal directions, namely perpendicular and parallel to the I-beam. The former incorporates the critical adhesively bonded connection which governs failure. The model incorporates material and geometric nonlinearities, appropriate interfacial and contact relations, robust failure criteria of the constituents, and was successfully verified using experimental results. The study showed that increasing the I-beam size by 33 % resulted in increasing the ultimate load (Pmax) by 25 %, mainly due to increasing the area of the adhesively bonded joint between the I-beam and SIP form. When mechanical fasteners were added to the connection, failure shifted to transverse rupture of the I-beam along its web-to-flange junction at a Pmax 1.8 to 2.8 times higher than that of adhesively bonded joint. A noticeable increase in cracking load occurred when the concrete strength varied 20 to 40 MPa, although led to slight change in Pmax due to failure still remaining by debonding. Increasing the slab thickness by 11 and 22 %, increased Pmax by 10 and 14 %, respectively, where debonding also governed. The floor behavior parallel to the I-beam was studied under different loadings and boundary conditions.

Joining in with the Move Away from PVC and PC

Joining techniques commonly used with polycarbonate and PVC – including adhesives and mechanical fasteners – are not effective on other resin choices. Didier Perret, medical business development manager at Emerson's Branson Welding and Assembly business, discusses the benefits of ultrasonic welding for these materials

Experimental and numerical study on the withdrawal behaviour of lag screws on wood side-grain

In wood connections using lag screws as mechanical fasteners, the tension force transfer mechanisms occur through the interaction between the screw threads and the wood surface. It is necessary to understand the screw withdrawal behaviour in order to make a simple but representative interaction model instead of modeling the geometry of the screw threads. This study aims to evaluate experimentally and numerically the withdrawal failure modes, stiffnesses, and capacities of lag screws on wood side-grain. The experiment is conducted on the withdrawal of lag screws with different diameters and penetration lengths in Meranti wood cubes. The numerical analysis is carried out using ABAQUS finite element program and compared with the experimental results. Both experimental test and numerical analysis results show that the failure of all specimens occurred in the wood around the hole, not due to the slip between the lag screw and the wood's surface, which validates the proposed interaction model between the screw and the wood’s surfaces. The wood's effective material stiffness and strength in numerical models are obtained by matching the load-displacement curves with the experiment results. The effective Fy value range is between 18.5 MPa - 24 MPa, while the effective E value range is between 115 MPa - 680 MPa.

Mechanical Fastening Methods of Polymer-Based Composites

Mechanical Fastening Methods of Polymer-Based Composites

Hard Nuts to Crack

Decades on, Hardlock nuts have proven their place as one of the most vibration-resistant mechanical fasteners available in the market. Sole UK distributor Staytite explains how they work, and how they have continued to benefit rail and other industrial applications

ОПЫТ ЛЕЧЕНИЯ БОЛЬНЫХ ПРИ ПОЛНОМ ОТСУТСТВИИ ЗУБОВ С ПРИМЕНЕНИЕМ ДВУХ ДЕНТАЛЬНЫХ ИМПЛАНТАТОВ

Despite the advances in modern dentistry, a steady increase in the number of patients with complete absence of teeth continues. From 30 to 70% of people need to make removable dentures. This is due to the imperfection of technologies, designs of dentures and materials for their manufacture, changing clinical conditions. The leading cause of clinical failure is poor stabilization of removable dentures on the jaws. In this regard, increasing the effectiveness of prosthetics in the absence of teeth is an urgent problem in modern dentistry. The article presents the experience of treating patients aged 60-75 years with a complete absence of teeth using two dental implants, a conditionally removable prosthesis, mechanical fasteners, and a spherical abutment. Implants of the systems Astra Tech, Nobel Biocare, Mis. We examined 33 patients aged 60-75 years, including 20 women and 13 men, with complete absence of teeth. 10 patients in the control group were made complete removable lamellar dentures. In 23 patients with severe atrophy of the alveolar processes, two dental implants were installed, followed by prosthetics according to the All-on-2 protocol. The follow-up period was 11 years. The data of the results of the observation indicated that in the control group, poor stabilization of the removable denture was registered, in three cases - its breakdown, in two patients, lesions of the oral mucosa were detected. In patients with dental implants, successful stabilization of removable dentures was noted with the preservation of the function of chewing, speech production and all articulatory relationships without damage to the oral mucosa.

Investigations on Factors Affecting 3D-Printed Holes Dimensional Accuracy and Repeatability

This paper investigates the impact of several factors related to manufacturing, design, and post-processing on the dimensional accuracy of holes built in the additively manufactured parts obtained by material extrusion process (MEX). Directly fabricated holes in the 3D prints are commonly used for joining with other parts by means of mechanical fasteners, thus producing assemblies or larger parts, or have other functional purposes such as guiding the drill in the case of patient-personalized surgical guides. However, despite their spread use and importance, the relationship between the 3D-printed holes’ accuracy and printing settings is not well documented in the literature. Therefore, in this research, test parts were manufactured by varying the number of shells, printing speed, layer thickness, and axis orientation angles for evaluating their effect on the dimensional accuracy of holes of different diameters. In the same context of limited existing information, the influence of material, 3D printer, and slicing software is also investigated for determining the dimensional accuracy of hole-type features across different manufacturing sites, a highly relevant aspect when using MEX to produce spare or end-use parts in a delocalized production paradigm. The results of this study indicated that the layer thickness is the most relevant influence factor for the diameter accuracy, followed by the number of shells around the holes. Considering the tested values, the optimal set of values found as optimizing the accuracy and printing time was 0.2 mm layer thickness, two shells, and 50 mm/s printing speed for the straight holes. Data on the prints manufactured on different MEX equipment and slicers indicated no statistically significant difference between the diameters of the holes. The evaluation of 3D-printed polylactic acid test parts mimicking a surgical template device with inclined holes showed that the medical decontamination process had more impact on the holes’ dimensional variability than on their dimensional accuracy.

Modelling and Optimization of Process Parameters during Grooved Hot Rolling of SAE 1020 Steel

ABSTRACT The rolled SAE 1020 steel bars are widely used for production of mechanical components, such as, gears, spindles, camshafts, axles, fasteners, and gudgeon pins etc. Steel industries have been striving for productivity and better yield of hot rolled bar products. The roll separating force (RSF), driving torque (DT), end crop length (ECL), and drive energy (DE) are the important response parameters to be controlled for quality production, maximization of yield (i.e. minimization of rolled bar process scrap), safety of mill and reduction in energy consumption, etc. These response parameters depend on several process parameters – rolling speed, billet temperature, reduction ratio, billet cross-section area, roll diameter, etc. This paper presents a study on the effect of the process parameters on the response parameters during rolling of SAE 1020 steel. Simulation of the rolling process has been attempted using FORGE® NxT 1.1. The simulated results so obtained have been validated through experimental results obtained in a rolling mill, following statistical tests. Regression models showing relationship between the process parameters and the response parameters have been developed. Significant model terms have been obtained using ANOVA. The optimum rolling conditions for minimization of the response parameters have been obtained.