Papers by Keyword: Bolted Joint

Abstract: The use of composite materials as a replacement for commonly used metals such as aluminium and steel are increasing in the engineering industry, particularly in the aerospace sector. The move towards light weight and high stiffness structures that have good fatigue durability and corrosion resistance has led to the rapid move from metal to composites. This change allows for further flexibility in design and fabrication of various components and joints. There are three main categories of joints used in composite materials – mechanically fastened joints, adhesively bonded joints and the combination of the two called hybrid joints. In order to adequately understand the effectiveness of these joints, substantial testing and validation is required, particularly in the use of hybrid joints for real life applications. Static testing, load distribution and parametric studies of hybrid joints have been investigated by various researchers; however further work is still required in understanding the durability and fatigue of hybrid joints and ensuring that both the adhesive and mechanical fasteners can work together effectively in producing an optimum joint. Mechanical fastening alone in composite laminates is not a preferred joining method as they create high stress concentrations around the fastener holes. Adhesive bonding although has numerous benefits it is difficult to detect the bond defect particularly in cases where weak bonds can occur during applications and it is sensitive towards the environmental conditions. Thus hybrid joints are seen arguably as being more effective in joining composite components together and offer greater residual strength. Hence the performance, strength and long-term durability of these joints need to be further investigated and be applied to practical situations whilst assisting in repair certification.

Abstract: The bolted joint is the important fastening parts of structures. Its fatigue and self-loosing will affect the safety of the system. In this paper, the finite element contact models are built to analyze the mechanical property of bolted joint numerically. The stress, strain and clamping force when the bolted joint is subjected to preload, axial force and transverse load are investigated. The results show that the bolt is the most dangerous part of bolt-nut connected member. The clamping force of bolted joint will gradually lose with the increasing loading cycles of cyclic transverse load which generally explains the stress loosing rule of bolted joint.

Abstract: The authors proposed fiber-optic-based damage monitoring of carbon fiber reinforced plastic (CFRP) bolted joints. Optical fibers were embedded along bolt holes and strain change along the optical fiber induced by internal damage was measured by a Brillouin Optical Correlation Domain Analysis (BOCDA), which is a high spatial resolution distributed strain sensing system. This study began by investigating damage modes of CFRP bolted joints after bearing failure. Effective embedding positions of optical fibers were then proposed and their feasibility was evaluated by finite element analysis simulating the damage propagation in the bolted joint and consequent strain change. Finally, verification tests were conducted using specimens with embedded optical fibers at various positions. It was clearly shown that damage could be detected using residual strain due to fiber-microbuckling (kinking) damage or permanent deformation of neighboring plies. Furthermore, damage size and direction could be estimated from the change in the strain distribution. The system developed is quite useful for a first inspection of large-scale composite structures in aerospace applications.

Abstract: The Brillouin optical correlation domain analysis (BOCDA) technology is one of the distributed optical sensing technologies utilizing the Brillouin scattering phenomena. The authors are developing, verifying and validating this technology. They are also developing the installation technique of optical fiber sensors, evaluating the durability of the BOCDA system and manufacturing the new device compatible to avionics bays for size. Furthermore, the authors are also improving the monitoring ability for composite damages. This paper reports the developmental status of the BOCDA monitoring ability for composite damages such as debonding at adhesive joints and micro-damages at bolted joints. First, debonding detection tests were conducted using carbon fiber reinforced plastics (CFRP) stiffened or repaired panels. In this test, test plates with a sheet stringer or a repair patch were applied tension load, and expanding of debonding areas was monitored by measuring strain distribution changes near these areas. Second, bearing damage detection tests were conducted using CFRP bolted joint specimens. In this test, multi-fastener single-lap CFRP specimens were applied tension load, and occurrences of micro-damages near bolt holes was detected. Micro-damages were detected by monitoring shapes changes of the Brillouin Gain Spectrum, which is one of the BOCDA measurement results.

Abstract: An experimental investigation was conducted to determine the bearing stress of single-lap double bolted composite joints. The bearing stress of a group of specimen was presented and the relationship between the stress and strain was obtained. The experimental results show that the damage of the bolted joints was a progressive process; and the ultimate bearing stress depends not only on the laminates’ strength but also on the bolt strength. A finite element model was created based on the bolted joint specimen to simulate the loading – displacement response. The numerical results verified the experiment results qualitatively.

Abstract: The results of an experimental investigation on the shear strength of structural joints are presented and discussed. Joint typologies generally employed in structural frames of industrial warehouses and intermediate floors are taken into consideration. Specimens were supplied by an industrial shelving manufacturer, in two different configurations: the first one characterized by steel pressed geometrical connectors and the second one consisting in bolted fittings to angular welded supporting plates. A specific testing device has been designed in order to transfer axial loading into shear loading applied to a couple of joints in a symmetrical testing configuration. Quasi-static loads were applied with increasingly intensity steps, until the yielding of the material or the overall structure collapse were reached. Failure modes of the tested joints are analyzed and discussed.

Abstract: To accurately analyze the force and deformation of the transmission tower, it is necessary to study performance of bolted joint in the tower. In the paper single shear and double shear bolted joint with number of bolts changed is tested. Based on the actual data in test, nonlinear finite element model of bolted joint is established with ABAQUS, considering the bolt clearance and preload, and shows good agreement with test results, which is proved correct and applicable. Eventually, through a comparison of FEM and test results, the factors that affect bolt slip and the changing relationship of axial force of bolt and friction force is described.

Abstract: Engineering assembly structures will suffer joint damage inevitably under environmental loads, which may affect the integrity and functionality of structures, even cause the catastrophic event. In the paper, a method using chaotic excitation and attractor geometrical property analysis to identify the joint damage is investigated. This method utilizes the property that different joint conditions will alter the filtered chaotic signal dimension. Damage features are extracted from reconstructed attractors and used to identify the joint condition. A new parameter based on the attractor local variance is tested as damage feature. An experimental jointed frame structures is designed and the joint damage are induced by varying the fastener preload. The results show that this approach works well for detecting the joint damage and the feature is monotonic varying with the damage increase.

Abstract: GLARE laminates with outstanding impact resistance, high fatigue resistance and a number of excellent performances are combined by ductile aluminum layers and high strength FRP layers. An experimental program was conducted to estimate the influence of geometric parameters, ply orientation and tightening torque on the performances of GLARE bolted joint. The study showed that the parameters of GLARE bolted joint have intrinsic properties of metal bolted joint and composite bolted joint. The design threshold values including of geometric parameters, ply orientation and tightening torque were given.

Abstract: Based on phenomenological method, the paper carried out experimental study for a kind of typical bolted joint structure, three kinds of testing specimens was designed, from the test result, the phenomenological model was obtained and the nonlinear mechanics behavior was comprehended, at last, the phenomenological model was verified experimental and numerical