Bolt Clamping Research Articles

Investigation of bolt clamping force on the fatigue life of double lap simple bolted and hybrid (bolted/bonded) joints via experimental and numerical analysis

In this research, the effect of bolt clamping force on the fatigue life of double lap simple bolted and hybrid (bolted/bonded) joints have been studied both experimentally and numerically. To do so, two kinds of joints, i.e. double lap simple and hybrid (bolted/bonded) joints were studied. For each kind of the joints, three sets of specimens were prepared and subjected to tightening torque of 1, 2.5 and 5Nm and then fatigue tests were carried out at different cyclic longitudinal load levels. Experimental tests revealed that the hybrid joints have higher fatigue life in comparison with the simple bolted joints. In the numerical method, finite element code was used to obtain stress distribution in the joint plates due to clamping force and longitudinal applied loads. Numerical simulation and experimental results showed that the fatigue life of specimens was improved by increasing the clamping force due to compressive stresses created around the hole. In addition, the investigation revealed the positive role of clamping force resulting from torque tightening on the fatigue life of both simple and hybrid joints.

Experimental Investigation on the Tensile Strength of Composite Laminates Containing Open and Filled Holes

An experimental study is performed to evaluate the effects of clamping pressure, friction, and washer size on the static performance of composite laminates with open and bolt-filled holes. The static tensile strength and failure behavior of composite laminates with an open hole and a bolt-filled hole are analyzed and compared. Experimental results show that the static tensile strength of composite laminates is sensitive to pre-existing damage of both open- or filled-hole laminates. In contrast, a comparison between the experimental results of open- and filled-hole specimens proved that whether the hole is open or filled has a feeble influence on the tensile-tensile fatigue strength of studied composite laminates. In comparison, however, it is found that the inserted washer size, bolt clamping force, and friction force strongly affect the tensile strength of open- and filled-hole composite laminates. Moreover, application of thicker washers and hi-lock bolt will significantly increase the static strength and fatigue life of composite laminates with a bolt-filled hole.

Investigating the effect of clamping force on the fatigue life of bolted plates using volumetric approach

In this paper, the effects of bolt clamping force on the fatigue life for bolted plates made from Al7075-T6 have been studied on the values of notch strength reduction factor obtained by volumetric approach. To attain stress distribution around the notch (hole) which is required for volumetric approach, nonlinear finite element simulations were carried out. To estimate the fatigue life, the available smooth S-N curve of Al7075-T6 and the notch strength reduction factor obtained from volumetric method were used. The estimated fatigue life was compared with the available experimental test results. The investigation shows that there is a good agreement between the life predicted by the volumetric approach and the experimental results for various specimens with different amount of clamping forces. Volumetric approach and experimental results showed that the fatigue life of bolted plates improves because of the compressive stresses created around the plate hole due to clamping force.

컴프레서 체결용 볼트의 적정 토크 설정에 관한 연구

When a threaded fastener is tightened, the torque-tension relationship is highly sensitive to two friction components: thread friction and head friction. In this study, we carried out friction experiments and analyses to determine the optimum clamping torque setting for bolt joints. First, we measured the coefficients of thread friction and head friction under the same running conditions of the bolt clamping process for lubricated and non-lubricated bolts. We also measured axial tension through bolt clamping tests using lubricated and non-lubricated bolts attached to a strain gauge. Finally, we compared the experiment and theoretical results.

유한요소해석법을 이용한 고정밀 반사경의 구조 해석

In this paper, the effect of bolt clamping force and form accuray of contact surface between mirror and mount on mirror surface was studied. Normally, mirror used in reflecting optical system was assembled with mount by bolts or adhesive. In this case, the tension caused by bolt clamping force or adhesive force may distort the mirror surface. Also, form accuracy error of the contact surface have a negative impact on wrenched mirror surface which assembled by bolts or adhesive. In this study, stress and distorted displacements on mirror surface were analyzed according to the different contact surface form accuracies and bolt clamping forces by using the finite element analysis method.

Effect of interference fitting and/or bolt clamping on the fatigue behavior of Al alloy 2024-T3 double shear lap joints in different cyclic load ranges

Two applied fatigue life improvement techniques of joints, interference fitting and bolt clamping, have been investigated comparing available experimental and finite element simulation results for Al-alloy 2024-T3 double shear lap joint specimens. Fatigue test results of interference fitted, bolt clamped and combined interference fitted-bolt clamped specimens were used to determine the effect of the different techniques on the fatigue life improvement in comparison with clearance fitted specimens. Also the fracture surfaces of the specimens were analyzed post-mortem to determine the fatigue crack initiation (and growth) locations. These locations were correlated to the applied cyclic load range. Results of the finite element analysis were used to help explain the trends observed in the experimentally obtained S-N data. Results showed that the fatigue life improvement not only changes for different techniques and magnitude of interference fit or tightening torque, but also depends on the applied cyclic load range.

The effect of electroless Ni–P coatings on the fatigue life of Al 7075-T6 fastener holes with symmetrical slits

In this paper, the fatigue behaviour of Al 7075-T6 fastener holes with symmetrical through slits was studied. The holes were coated with electroless nickel (EN) plating with a high phosphorous content of 10–13wt% and a thickness of 40μm. Uncoated open-hole, EN coated open-hole, uncoated bolted hole and EN coated bolted hole specimens were fatigue tested. Bolted samples were clamped with a high tightening torque of 7Nm. The established S–N curves showed 282–1348% improvements in the fatigue life due to the combined effect of EN coating and bolt clamping, depending on the level of maximum alternating stress. Excellent adhesion was observed between the coating and the aluminium substrate along the crack path. Tensile tests results showed a considerable reduction of 54% in the ductility of the coated material while both the yield and ultimate strengths were found to slightly increase by approximately 6% in comparison with the uncoated aluminium alloy.

Finite element investigations of bolt clamping force and friction coefficient effect on the fatigue behavior of aluminum alloy 2024-T3 in double shear lap joint

In this paper, the effect of bolt clamping force on the fatigue life of bolted double shear lap joints was investigated numerically. To do so, finite element simulation results were used to illustrate the trends occurred in experimental fatigue tests showing the effect of bolt clamping on improving the fatigue life of double shear lap joints. The results show that clamping force decreases the resultant longitudinal stress at the hole edge thus the fatigue life increases compared to clearance fit specimens. In general, at higher tightening torque longer fatigue lives were achieved, however, below a certain load level the life improvement was discontinued because of fretting occurrence. Also lubricating the specimens reduces the advantages of the clamping force.

A detailed finite element investigation of composite bolted joints with countersunk fasteners

This paper presents a very detailed FE model of a single lap composite bolted joint, with countersunk fasteners, under static tensile load. The stress states of the CFRP plates and titanium bolts are discussed, the evolution of the contact between the bolts and the holes is analysed, and the numerical results are compared to experimental data. Parametric studies have been performed to study the influence of bolt clamping force, coefficient of friction and bolt–hole clearance on the joint behaviour. It has been found that the model is able to identify correctly the critical locations in the joint (head–shank transition and first thread in bolts and edges of the holes at the faying surface for the plates) and reproduce with accuracy the experimental load–displacement test curves (including an unloading–reloading loop) up to the point where bearing damage occurs. A correlation between the joint stiffness and the contact status between bolts and holes has been found. Five stages have been identified in the joint behaviour: (i) No-Slip, (ii) Slip, (iii) Full Contact, (iv) Damage and (v) Final Failure. The results show that the joint stiffness is higher in the No-Slip stage than in the Full Contact stage, and that this is independent of coefficient of friction and bolt clamping force. The clearance controls the length of the Slip stage and modifies the joint stiffness in the Full Contact stage.

Effect of bolt clamping force on the fracture strength of mixed mode fracture in an edge crack with different sizes: Experimental and numerical investigations

To investigate the effect of bolt clamping force, resulting from torque tightening, on the mixed mode fracture (I and II) strength and effective geometry/loading factor of an edge crack with different lengths, experimental and numerical studies have been carried out. In the experimental part fracture tests were conducted on three batches of simple edge crack and bolt torque tightened with 3.5 and 7Nm edge crack at three different crack sizes of Poly methyl-methacrylate (PMMA) rectangular plate. The specimens’ fracture strength was obtained using a tensile test machine at different loading angles by employing a modified Arcan fixture. In numerical part, finite element simulations were employed to model the three test specimen batches at the three crack lengths to obtain their stress intensity geometry/loading factors. The results show that the bolt tightening torque significantly reduces the effective geometry/loading factor, and thus increases the joint fracture strength compared to bolt-less simple edge crack specimens. However, the bolt clamping effect on increasing the fracture strength was almost the same for different crack lengths.

Effect of cold expansion and bolt clamping on fretting fatigue behavior of Al 2024-T3 in double shear lap joints

In this paper the fatigue behavior of double shear lap joints treated by cold expansion and bolt clamping has been investigated. Fatigue tests and numerical simulations were conducted to study the combined effect of cold expansion and bolt clamping on the fatigue life and failure mode. The results showed significant changes on the fatigue behavior of the double shear lap joints at different load ranges. Depending on the degree of cold expansion and clamping torque, both plain fatigue and fretting fatigue failures were observed. The optimum degree of cold expansion in conjunction with the clamping force differs from those reported for joints that were cold expanded only.

Investigating clamping force variations in Al2024-T3 interference fitted bolted joints under static and cyclic loading

In this paper the variation of bolt clamping force in interference fitted-bolt clamped aluminum 2024-T3 specimens in double shear lap joints have been investigated under static and cyclic loads. In experimental part of the study, static or cyclic longitudinal remote loads have been applied to the joint and the variations of bolt clamping forces were measured in the tests. Finite element analysis was also performed and the results were compared with the results of statically loaded experimental tests. The results showed an initial reduction of the clamping force followed by an increase for bigger longitudinal static load. During cyclic loading in experimental tests, bolt clamping force reduction was observed in the first 1000 cycles, especially for joints with higher size of the interference fit. This reduction was due to the scrape of the protruded region around the hole, left from bolt interference fitting, on the exit plane of the main part.

Investigating bolt clamping force effect on the mixed mode fracture strength and stress intensity factor for an edge crack in PMMA specimens

► The fracture strength of bolted specimens is greater than the simple edge crack specimens. ► The fracture strength of the PMMA specimens in mode II is bigger than mode I. ► The geometry factor of both modes I and II decreases when the specimen is bolt clamped. Experimental and numerical investigations have been conducted to evaluate the effect which the clamping force, resulting from torque tightening a nut and bolt, has on the mixed mode (I and II) fracture strength and effective stress intensity geometry/loading factor of a plate having an edge crack. The experimental tests were carried out on three batches of simple edge crack and bolt torque tightened edge crack specimens made from poly methyl-methacrylate (PMMA) rectangular plate. The specimens’ fracture strengths were obtained using a tensile testing machine in different loading angles using a modified Arcan fixture. In numerical part, finite element simulations were used to model the three test specimens variants used and thereby establish their stress intensity geometry/loading factors. The results show that the bolt tightening torque, and hence the plate clamping force, has a significant effect on reducing the equivalent mixed mode stress intensity factor of all loading angles and the equivalent factor, and thus the joint fracture strength compared to bolt-less simple edge crack specimens.

Experimental and numerical investigations about the combined effect of interference fit and bolt clamping on the fatigue behavior of Al 2024-T3 double shear lap joints

In this paper the fatigue behavior of double shear lap joints treated by different combinations of interference fit and bolt clamping have been investigated both experimentally and numerically. To do so, specimens made from aerospace structural material of aluminum alloy 2024-T3 plates were interference fitted at the sizes of 1.5% and 4.7% and torque tightened with 2 and 4 N m to be prepared for fatigue tests. Consequently, the joints were subjected to cyclic load at different levels to obtain fatigue life. Finite element (FE) analysis was also performed to find the stress and strain distributions and the results were used to help explain the trends observed in the experimentally obtained S–N data. The experimental tests showed that during the interference fit process a protruded region is created at around the hole in the exit plane due to directional material plastic flow as a consequence of the oversized bolt force fitting. This protruded region has a bigger height for the bigger interference fit size. The finite element results showed that the protruded region generally localizes the compressive effect of bolt clamping and reduces its capability in fatigue life enhancement, by relaxing the clamping force. The fatigue test results showed that a better fatigue life improvement was achieved by employing the combination of a smaller interference fit size and bigger clamping force.

An experimental investigation of the bolt clamping force and friction effect on the fatigue behavior of aluminum alloy 2024-T3 double shear lap joint

In this article, the effect of bolt clamping force on the fatigue life of bolted double shear lap joints was investigated. To do so, fatigue tests were carried out on the bolt clamped double shear lap joint specimens made of aluminum alloy 2024-T3. These fatigue tests were conducted with applied torques of 0.25, 2 and 4 N m at different cyclic longitudinal load levels in un-lubricated and lubricated states. From these tests the stress–life ( S– N) data for different clamping forces for un-lubricated and lubricated states were obtained. The results show that clamping force increases fatigue life compared to clearance fit specimens. In general, at higher tightening torque higher fatigue lives were achieved, however, below a certain load level the life improvement was discontinued because of fretting phenomenon. Also lubricating the parts of the specimens reduces the advantage of clamping force or torque tightening.

On the fatigue behavior of cold expanded fastener holes subjected to bolt tightening

Cold expansion literature has been generally devoted to open hole specimens. Nevertheless, cold expanded specimens are practically used in bolted and riveted connections possessing different fatigue behavior than open hole specimens. This paper has sought to investigate the fatigue behavior of cold expanded specimens after being subjected to bolt tightening. Fatigue tests and numerical simulation were conducted to study the role of bolt clamping force on the residual stress distribution, fatigue life and failure mode of bolted cold expanded specimens. The results significantly reveal that bolt clamping contributes more positive effect and prolongs the fatigue life additionally. However, it may also change the failure mode from notch fatigue to fretting fatigue.

Perancangan Fixture Proses FreisUntukProduksi Komponen Sambungan Karburator

The tools are designed to assist and simplify the machining process, and increase the number of products that can be manufactured with quality maintained. The tools aredesigned to use in the manufacture of the carburetor connection with the Freis. Freisprocess here to cut the work piece that originally shaped like a rectangle into a rhombus.The tool is made by using the principle of supporting and supported by the use ofclamping. Supporting made with a flat surface so that the entire supporting surface is assumed to touch the entire workpiece. Meanwhile, the use of bolt clamping aims to unifyworkpieces with supporting so that the workpiece can not be separated and do not moveduring the machining process takes place. This is evidenced by the equation forcesgenerated by the clamping, the force generated is positive so that the proper tool to use.With this tool, production time becomes shorter and the resulting product is also more precise so that the quality and quantity of product is assured. Production costs necessaryto complete the carburetor connection is also cheaper than without using tools. Keywords: fixture, carburator, freis

Investigation of the fatigue life and crack growth in torque tightened bolted joints

The fatigue crack initiation and fatigue crack growth life estimations have been numerically investigated and the total estimated fatigue lives have been compared with available experimental fatigue test results for a single plate of aluminum 7075-T6 bolted with different applied torques. To do so, pre-stresses around the hole due to the torque tightened bolt and stress concentration factor of the combined longitudinally applied load and bolt clamping force were determined using 3D finite element simulations results. The calculated pre-stresses and stress concentration factors for different bolt clamping forces were employed in AFGROW computer package to predict fatigue crack initiation and fatigue crack growth lives. The results show that there is good agreement between the numerically predicted total fatigue lives and available experimental fatigue test results. The numerical results also show that bolt clamping force increases both fatigue crack initiation and fatigue crack growth lives individually.

The conceptual alternative design for ITER magnet gravity support using clamp bolt

In the original reference design of ITER Toroidal Field (TF) gravity support pedestal, the 21 flexible plates are welded to the top and bottom flanges with a 19 mm gap in any two adjacent flexible plates. Fabricating is very difficult for this design. In order to avoid welding, an alternative design for the ITER TF gravity support pedestal, called as “Bolt Clamping Option”, is purposed to substitute for the original one. The detailed design is introduced in this paper. The structural analysis has been performed using ANSYS. The analysis results show that the alternative design is safe, no obvious stress concentration. Therefore it could be seen in the ITER construction.

Prediction of fatigue performance of fastener holes with bolt clamping force based on critical plane approach

In the present study, a series of fatigue tests are conducted on aluminum alloy 2024 to investigate fatigue behavior of fastener holes in reverse double bone specimens. With reference to the finite element results, the fatigue lives of fastener holes in reverse double bone are predicted based on critical plane approaches, including Smith–Watson–Topper (SWT) model and Wang–Brown (WB) model. After that, the predicted values are compared with that from tests. At last, under different far field stress levels, the effect of bolt clamping force on fatigue life of fastener holes is predicted based on the aforementioned two models. The results show that the SWT approach achieves a better accuracy than the WB approach for high cycle fatigue (HCF) while the opposite holds for low cycle fatigue (LCF). The fatigue life of fastener holes decreases with the increase of bolt clamping force.