Furthermore, the relationship between the torsion moment and the torque transmitted to the bolt shank was also determined. Figure: 4.9 (a) Curve-I, the uniaxial tensile load vs. strain on the 65-bolt curve, (b) Curve-2, preload developed on the bolt head. versus bolt extension without lubricant.
JUSTIFICATION
The design and installation of bolted joints must ensure that the joint remains tight and that the fastener is capable of withstanding the static and dynamic loads applied. How tight should the bolt be and what assurance is there that the assembly process can consistently achieve this level of tightening.
OBJECTIVES
LAYOUT OF THE THESIS
This tightening torque will develop pre-load on the bolt and this pre-load will depend on the lubrication condition of the mating surface. Tensile stresses are approximately constant throughout the bolt section, but torsional stresses increase from zero at the center to a maximum at the outer surface.
PREVIOUS WORK
Mechanics of Bolted Joint
Where Pb is the proportion of the external load P taken by the bolt and Kb is the spring constant of the bolt. When the bolt is tightened, the load on the bolt increases and the deformation of the bolt increases.
![Fig - 2.2 Force deflection of a bolt under loading [15]](https://thumb-ap.123doks.com/thumbv2/filepdfnet/10829699.0/26.834.146.683.222.598/fig-2-2-force-deflection-bolt-loading-15.webp)
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INTRODUCTION
In this study, the focus was on observing the performance characteristics of a well-tightened screw under external loading. In the present investigation, we also studied the influence of other parameters on the mechanical properties of the screw itself. A test rig along with auxiliary components/parts was designed to carry out a detailed experimental investigation of the joint screw.
DESCRIPTION OF THE TEST RIG
After tightening a bolt to the various level of torque, the test rig can be disassembled in such a way that it can be set up in a universal testing machine and external tensile loads can be applied to that part of the test setup.
DETAIL OF THE COMPONENTS .1 Load Cell
In this experiment it was used to transfer the developed preload in the bolt to the load cell. One in the center of the base plate and the other two opposite the center hole. A total of two base plates were used in this experiment, one at the top of the load cell and another at the bottom of the load cell.
The position of the base plates in relation to the weighing cell is shown in Figure 3.1. In this experiment, it was used to tighten the test bolt against the load cell by means of two base plates. The hexagonal nut was installed so that it can hold the screw in a tight state against the measuring cell during disassembly.
Generally, lower plate is fixed with the work table with nut bolt arrangement and upper plate holds the part of the test rig. The section of the test rig containing test bolt, load cell, two base plates and a hexagonal nut is shown in figure 3.14.
TESTING BOLT
SPECIAL ATTACHMENT FOR TENSILE TEST
SPECIAL ATTACHMENT FOR APPLYING EXTERNAL LOAD Figure-3.9 represents the schematic diagram of a special attachment for
AUXILIARY EQUIPMENT .1 Universal Testing Machine
- Torque Testing Machine
- Torque Wrench
- Data Acquisition Equipment a. Strain Meter
The adhesive has been applied to the bolt surface as well as under the surface of the strain gauge. Figure-3.11 represents the applied compressive load vs. strain gauge reading of the strain gauge attached to the load cell. Applied known compressive load was recorded from the universal testing machine and its corresponding load of the load cell was recorded from the strain gauge.
Figure-3.l2 represents the variation of torque applied to a torque load cell with the output reading (mv) obtained from a multimeter. Figure-3.l3 represents the applied torque on the bolt head versus the strain gauge reading of a shear stress gauge attached to the surface of the bolt. The connection of the torque load cell strain gauge was made with a strain gauge in accordance with. the shaft of the dial touched the free end of the test screw.
With the extension of the bolt, the pointer on the dial gauge deflected and the reading was recorded. Torque load cell reading was recorded by the multimeter and bolt elongation was measured by the extensometer.
INTRODUCTION
It can also be seen from the figure that the clamping load developed in this way also changes for different lubrication conditions. It can be seen from the figure that for 88 (N-m) applied wrench torque, the preload developed for no lubrication, with VG-15 lubrication and VG-46 lubrication is 17 kN, 20.5 kN and 24.7 kN, respectively. It was also calculated that the preload increased by 22% when using VG-15 lubricant and 47% when using VG-46 lubricant compared to those without lubricant.
Therefore, it can be concluded that preload development will be higher when higher viscosity grade lubricant is used. From figure.-4.2 it can be concluded that the friction between the bolt under head and fitting surface has a great influence on the development of preload due to applied torque. When friction condition deteriorates, a greater torque is required to achieve a given level of preload.
So, by improving the coefficient of friction between the surfaces, the preload developed in the bolt due to the applied tightening torque can be increased.
Torque Transmission From the Bolt Head to the Shank
Therefore, it can be concluded that the applied torque transfer to the bolt stem depends on the frictional conditions between the bolt under the head and the bearing surface.
Tightening of the Bolt Into the Plastic Region
However, the total elongation of the bolt due to tightening in the plastic region decreases than for a new bolt.
Effect of External Load on Tightened Bolt
- GENERAL
When the applied external load increases to 30.38 kN, the stem torque decreases to 14 N-m at 4 mm bolt elongation, which means that the stem torque is reduced by about 53%. In addition, it was found in Figure 4.16 that when the external tensile load reaches almost the same ultimate load, the reduction in stem torque ceases and the available stem torque remains as the residual bolt torque. It can be seen from the figure that when the external tensile load reaches almost equal to the ultimate load, the stem torque decreases to 10.75 N-m at a bolt elongation of 12 mm, which means that the maximum stem torque reduction was 65%.
Then the applied external load increased up to 32 kN, the shaft torque decreases to 16 N-m at 4.5 mm bolt extension, i.e., the shaft torque decreases to 55%. Furthermore, it was observed from the figure that when the external tensile load reaches almost equal to its ultimate load, the reduction of arm torque ceases and the torque available at the shaft remains as the residual torque of the bolt. It is observed from the figure that when the external tensile load reaches almost equal to the ultimate load, the residual arm torque decreases to 11.5 N-m. with the 10 mm extension of the bolt, i.e. the arm torque is reduced to 67%.
Furthermore, it was seen from the figure that when the external tensile load is almost equal to the ultimate load, the reduction in shank torque ceases and the available torque in the shank of the bolt remains as the residual torque of the bolt. The figure also shows that when the external tensile load is almost equal to the ultimate load, the residual shaft torque decreases to 11.5 N-m when the bolt is extended by 10 mm, that is, the shaft torque decreases by about 70%.
RECOMMENDATION
- General
The torque transfer to the bolt shank without lubrication was 52%, with lubrication by VG-15 and VG-46 62% and 68%, respectively. Thus, it can be concluded that the higher the higher viscosity lubricant used, the higher the rate of torque transfer to the bolt shank and therefore the higher the preload developed. vi). It was observed that when the bolt was tightened to the combined yield point or beyond (i.e. in the plastic region), the maximum tensile load capacity of the bolt remains unaffected. vii).
It was further observed that the lubrication condition has no effect on the maximum load capacity of the bolt. ix). Axial tensile load and torsional load have several effects on the bolt thread, which will be considered to get the best possible result. iv). The sudden change of bolt TPI dimension and type has got some stress concentration effects, to get the best possible result, due consideration will be given to the stress concentration factor. c).
When the external tensile load was applied to the tightened bolt, a special adjustment must be made to measure the bolt elongation accurately to obtain the best possible result, which was not possible in this experiment. vi). Torsion has no effect on the maximum load carrying capacity, so the bolt must be designed based on the uniaxial tensile behavior of the bolt material!.
STRAIN METER
I S.TRAIN GAUGE I
BOLT-C ,
FIGURE-3.13 The relationship between the torque (N-m) applied at the bolt head and the corresponding micro-strain reading of the torsional displacement strain gauge fitted to the bolt shaft recorded by the strain gauge. FIGURE-4.1 The uniaxial tensile load applied to the bolt by a universal testing machine versus the corresponding elongation of the bolt measured by the extensometer. FIGURE-4.2 The relationship between the torque (N-m) applied at the bolt head and preload.
FIGURE-4.3 Relationship between the torque (N-m) acting on the bolt head and the amount of torque (N-m) transmitted to the bolt shank without lubrication. FIGURE-4.5 The relationship between the screwdriver torque (N-m) acting on the screw head and the amount of torque (N-m) transferred to the screw shank by VG-15 lubrication. FIGURE-4.6 The relationship between the torque of the screwdriver (N-m ) acting on the screw head and the amount of torque (N-m) transmitted to the vibration of the screw by lubrication with VG-15.
FIGURE-4.7 The relationship between the torque (N.m) applied at the bolt head and the amount of torque (N.m) transmitted to the shank of the bolt with lubrication by VG-46. FIGURE-4.8 The relationship between the torque (N-m) applied at the bolt head and the amount of torque (N-m) transmitted to the shank of the bolt with lubrication by VG46. Represents the external load applied to the bolt vs. elongation of the bolt without lubrication condition.
FIGURE-4.18 (a)Curve-1, Represents the state of rotation of the bolt arm in relation to the elongation of the bolt when the external tensile load is applied. (b) Curve-2, Represents the external load applied to the bolt versus the elongation of the bolt in the condition of lubrication by VG-46.
![Figure 2.7 Torsion of a solid cylindrical bar (a) Plastic annulus and stress distribution for H=O (b) Torque-angle of twist relationship .r 22]](https://thumb-ap.123doks.com/thumbv2/filepdfnet/10829699.0/33.834.132.718.434.862/figure-torsion-cylindrical-plastic-annulus-distribution-torque-relationship.webp)
