A Loosening Mechanism of Bolted Joints Under Repeated Transverse Displacements

2012 ◽  
Author(s):  
Toshiyuki Sawa ◽  
Mitsutoshi Ishimura ◽  
Takanori Nagao
Keyword(s):  
Testing Machine ◽  
Bolted Joints ◽  
Impact Loads ◽  
Screw Thread ◽  
Spring Plate ◽  
Thermal Changes ◽  
Good Agreement

Loosening accidents sometimes occur under several types of loadings such as winds, vibrations, earthquakes, impact loads and thermal changes. Recently, some studies have been conducted on the screw thread loosening in bolted joints under repeated transverse displacements. It is well known that bolted joints are easily loosened when repeated transverse loadings are applied [1]. In assembling bolted joints, double nut, spring plate washers and hexagon nuts with flange have been used. However, a few studies have been carried out on the loosening mechanism in bolted joints with the above parts for preventing the loosening. In the present paper, the effects of the double nut, spring plate washers and hexagon nuts with flange mentioned above are examined using FEM calculations. The experiments to measure the loosening in bolted joints were carried out using Junker’s testing machine for validation of the FEM calculations. As the results, it is seen that the loosening speed is the maximum when the hexagon nuts with flange is used. In addition, it is also observed that bolted joints in which almost nut parts for preventing loosening are applied are loosened easily in the FEM calculations. The amounts of loosening for bolted joints with double nut, spring plate washers and hexagon nuts with flange are in a fairly good agreement with the measured results. Discussion is made on the loosening mechanism of bolted joints with the above parts under repeated transverse displacements.

A Bolt-Nut Loosening Mechanism in Bolted Connections Under Repeated Transverse Loadings (Effect of Inclined Bearing Surfaces on the Loosening)

2010 ◽  
Author(s):  
Toshiyuki Sawa ◽  
Mitsutoshi Ishimura ◽  
Atsushi Karami
Keyword(s):  
Testing Machine ◽  
Bolted Joints ◽  
Incline Angle ◽  
Impact Loads ◽  
Screw Thread ◽  
Bolted Joint ◽  
Bearing Surface ◽  
Bolted Connections ◽  
Inclined Surfaces ◽  
Thermal Changes

Loosening accidents sometimes occur under several types of loadings such as winds, vibrations, earthquakes, impact loads and thermal changes. Recently, some studies have been conducted on the screw thread loosening in bolted joints under repeated transverse loadings. It is well known that bolted joints are easily loosened when repeated transverse loadings are applied. While, in assembling bolted joints, the contact surfaces between a bolt head/nut and a clamped part are inclined geometrically. However, a lot of researches have dealt with the bolted joints in which the bearing surfaces are perfectly contacted without the inclined surfaces. Thus, it is necessary to examine the incline of the bearing surfaces on the loosening in bolted joint. A lot of parts for preventing the loosening have been proposed and sold at market. Among these parts, the authors have demonstrated that eccentric nuts are especially expected to be the solution for preventing the loosening of the joints under repeated transverse loadings. However, a few studies have been carried out on the loosening and loosening mechanism in bolted joints with inclined bearing surface and the effective solution for preventing loosening of bolted joint with the inclined bearing surfaces under the repeated transverse loadings. Thus, it is necessary to examine the effect of the incline at the bearing surfaces on the loosening and to evaluate the solutions for preventing loosening of the bolted joints with the inclined bearing surfaces. In this study, the effect of the incline at the bearing surfaces on the loosening is examined using FEM calculations. In the FEM calculations, the incline angle at the bearing surfaces is changed as 0, 2 and 3 degree, respectively. The experiments to measure the loosening in bolted joints were carried out using Junker’s testing machine to validities of the FEM calculations for revealing the effect of the loosening in the joints with the inclined bearing surfaces. In addition, nut parts for preventing the loosening in bolted connections with the inclined bearing surface under repeated transverse loadings are examined using the FEM calculations. As the result, it is seen that the loosening increases as the angle of incline increases. In addition, it is observed that bolted joints in which almost nut parts for preventing loosening are applied are loosened easily while the eccentric nut does not loosened. Discussion is made on the loosening mechanism in bolted joints under repeated transverse loadings.

Mechanical Behavior of Rotational Screw Thread Loosening in Bolted Joints Under Repeated Temperature Changes

2008 ◽  
Author(s):  
Toshiyuki Sawa ◽  
Mitsutoshi Ishimura ◽  
Yasumasa Shoji ◽  
Yusuke Fukuba
Keyword(s):  
Finite Element Method ◽  
Finite Element ◽  
Mechanical Behavior ◽  
Experimental Results ◽  
Bolted Joints ◽  
Screw Thread ◽  
Bolted Joint ◽  
Temperature Changes ◽  
Thermal Changes ◽  
The Difference

Bolted joints have been used in mechanical structures. However, loosening accidents sometimes happen under several types of loadings. Recently, some studies have been conducted on the screw thread loosening in bolted joints. It is verified that bolted joints are loosened when transverse repeated loadings are applied. A lot of parts for preventing the loosening in the joints have been proposed. Among these parts, eccentric nut is especially expected to be the solution for preventing the loosening. Some studies on no rotational loosening in bolted joints under thermal changes have also conducted. However, few studies on rotational screw thread loosening in bolted joints have conducted. In our previous study, mechanism of rotational screw thread loosening in bolted joint under repeated temperature changes was examined. However, the difference in the loosening mechanism between the FEM results and the experimental results was substantial. In this study, the effect of the incline at the bearing surfaces was taken into consideration on the loosening. In addition, the loosening in the bolted joint with the eccentric nut under repeated temperature changes was examined using finite element method (FEM) calculations. Discussion is made on the mechanism and a solution of rotational screw thread loosening in the bolted joints under the repeated temperature changes. The results show that a reduction in axial bolt force was increased when the incline at the bearing surfaces was taken into consideration and the eccentric nut was shown for preventing the bolt loosening.

Mechanism of Screw Thread Loosening in Bolted Joints With Dissimilar Clamped Parts Under Repeated Temperature Changes

2014 ◽  
Author(s):  
Mitsutoshi Ishimura ◽  
Shunichiro Sawa ◽  
Yuya Omiya ◽  
Toshiyuki Sawa
Keyword(s):  
Relative Displacement ◽  
Bolted Joints ◽  
Test Machine ◽  
Screw Thread ◽  
Temperature Changes ◽  
Rotational Deformation ◽  
Measured Change ◽  
Bolt Loosening ◽  
Rotational Load ◽  
Good Agreement

It is well known that bolted joints are sometimes loosened under transverse repeated loadings. Recently, some studies have been carried out on the mechanism of the bolt loosening under transverse repeated loadings. In the present research, the mechanism of bolt loosening was examined for a bolted joint using Junker’s type loosening test machine under transverse repeated loadings. Furthermore, a rotational deformation of bolt axis and nut was analyzed using FEM. As a result, it is found that the rotational load is applied and the bolt loosening occurs due to the deformation between the bolt axis and the nut. The measured change in axial bolt force was fairly good agreement with the numerical results. In addition, the bolt loosening in bolted joints with dissimilar clamped parts was examined under temperature changes. Due to the temperature changes, it is assumed that a relative displacement among the bolt bearing surface and the bearing surfaces of the clamped parts and then it is found that a bolt loosening occurs. In FEM calculations, the behavior of the bolt loosening was examined and found to occur a slight loosening. In the experiments, the bolt loosening was measured under temperature changes. The material of dissimilar clamped parts is assumed steel and aluminum. The thickness of the clamped parts is 10mm. The tendency of the bolt loosening is fairly coincided between the numerical and the measured results. It was observed that the bolt loosening occurred easily as the clamped length (gap length) decreased. In the FEM calculations, the slope θ of the bearing surfaces between the bolt head and the clamped part is assumed to be 0.5 degree to 2 degree. The effects of the slope of the bearing surfaces and on the bolt loosening are examined in the FEM calculations. The calculated results are in a fairly good agreement with the measured results. As the conclusions, 1) the bolt loosening of bolted joints under transverse repeated loadings was elucidated using 3-D FEM calculations, 2) Under repeated temperature changes, it was found that the bolt loosening occurred due to the slips between the bearing surfaces and the interfaces of clamped parts. Using FEM calculations, the behavior of the bolt loosening was elucidated.

scholarly journals Design analysis of four-wave-mixing in SiN nanowires integrated with graphene oxide films

2020 ◽  
Author(s):  
David Moss
Keyword(s):  
Graphene Oxide ◽  
Kerr Nonlinearity ◽  
Four Wave Mixing ◽  
Wave Mixing ◽  
Trade Off ◽  
Material Parameters ◽  
Highly Nonlinear ◽  
Thermal Changes ◽  
Strong Mode ◽  
Good Agreement

<p>We theoretically investigate and optimize four-wave mixing (FWM) in silicon nitride (SiN) waveguides integrated with two-dimensional (2D) layered graphene oxide (GO) films. Based on extensive previous measurements of the material parameters of the GO films, we perform detailed analysis for the influence of device parameters including waveguide geometry, GO film thickness, length, and coating position on the FWM conversion efficiency (CE) and conversion bandwidth (CB). The influence of dispersion and photo-thermal changes in the GO films is also discussed. Owing to the strong mode overlap between the SiN waveguides and the highly nonlinear GO films, FWM in the hybrid waveguides can be significantly enhanced. We obtain good agreement with previous experimental results and show that by optimizing the device parameters to balance the trade-off between Kerr nonlinearity and loss, the FWM CE can be improved by as much as ~20.7 dB and the FWM CB can be increased by ~4.4 folds, relative to the uncoated waveguides. These results highlight the significantly enhanced FWM performance that can be achieved in SiN waveguides by integrating 2D layered GO films.<i></i></p>

scholarly journals Development of n-DoF Preloaded Structures for Impact Mitigation in Cobots

2018 ◽  
Vol 10 (5) ◽  
Author(s):  
S. Seriani ◽  
P. Gallina ◽  
L. Scalera ◽  
V. Lughi
Keyword(s):  
Three Dimensional ◽  
Impact Loads ◽  
Single Degree Of Freedom ◽  
Impact Mitigation ◽  
Single Degree ◽  
Future Developments ◽  
Core Issue ◽  
Comprehensive Framework ◽  
Peculiar Behavior ◽  
Good Agreement

A core issue in collaborative robotics is that of impact mitigation, especially when collisions happen with operators. Passively compliant structures can be used as the frame of the cobot, although, usually, they are implemented by means of a single-degree-of-freedom (DoF). However, n-DoF preloaded structures offer a number of advantages in terms of flexibility in designing their behavior. In this work, we propose a comprehensive framework for classifying n-DoF preloaded structures, including one-, two-, and three-dimensional arrays. Furthermore, we investigate the implications of the peculiar behavior of these structures—which present sharp stiff-to-compliant transitions at design-determined load thresholds—on impact mitigation. To this regard, an analytical n-DoF dynamic model was developed and numerically implemented. A prototype of a 10DoF structure was tested under static and impact loads, showing a very good agreement with the model. Future developments will see the application of n-DoF preloaded structures to impact-mitigation on cobots and in the field of mobile robots, as well as to the field of novel architected materials.

Lateral Collapse of Woven-Fabric Composite Tubes under Quasi-Static and Impact Loads

2011 ◽  
Vol 82 ◽  
pp. 296-301
Author(s):  
Sripad S. Tokekar ◽  
Maloy K. Singha ◽  
Narinder K. Gupta
Keyword(s):  
Progressive Failure ◽  
Woven Fabric ◽  
Collapse Mechanism ◽  
Impact Loads ◽  
Composite Tubes ◽  
Finite Element Software ◽  
Progressive Failure Analysis ◽  
Numerical Predictions ◽  
Fabric Composite ◽  
Good Agreement

An experimental investigation on the lateral collapse behaviour of woven fabric glass/epoxy composite tubes under quasi-static and impact loads are presented here. Composite tubes of different diameter to thickness ratios (D/t = 5.33 - 20.67) were compressed between two flat platens or by a short width square indenter. Impact tests were performed at the gravity drop hammer test setup. The fracture process and the energy absorption capability of the composite tubes under quasi-static and impact loads were studied. It was observed that, the lateral collapse mechanism of thick composite tubes (D/t < 10) was different from thinner tubes (D/t > 10). Finally, the progressive failure analysis of the composite tube was performed in finite element software ABAQUS. Good agreement was observed between the experimental results and numerical predictions.

The Effect of the Carbon Epoxy Plate’s Size under Low Velocity Impact

2008 ◽  
Vol 587-588 ◽  
pp. 951-955
Author(s):  
Ana M. Amaro ◽  
Paulo N.B. Reis ◽  
Marcelo F.S.F. de Moura
Keyword(s):  
Numerical Analysis ◽  
Testing Machine ◽  
Three Dimensional ◽  
Experimental Tests ◽  
Low Velocity Impact ◽  
Rectangular Plates ◽  
Low Velocity ◽  
Velocity Impact ◽  
Impact Energies ◽  
Good Agreement

The aim of present work is to study the influence of the plate’s size on low velocity impact on carbon-fibre-reinforced epoxy laminates. Experimental tests were performed on [04,904]s laminates, using a drop weight-testing machine. Circular, square and rectangular plates were tested under low velocity impacts using a hemispherical impactor with 20 mm diameter and 3 J impact energies. The impacted plates were inspected by X-radiography. Numerical simulations were also performed considering interface finite elements compatible with three-dimensional solid elements, which allows to model delamination onset and growth between layers. The results showed that the plate’s size has influence on the delaminated area. Good agreement between experimental and numerical analysis for shape, orientation and size of the delaminations was obtained.

Design analysis of four-wave-mixing in SiN nanowires integrated with graphene oxide films

2020 ◽  
Author(s):  
David Moss
Keyword(s):  
Graphene Oxide ◽  
Kerr Nonlinearity ◽  
Four Wave Mixing ◽  
Wave Mixing ◽  
Trade Off ◽  
Material Parameters ◽  
Highly Nonlinear ◽  
Thermal Changes ◽  
Strong Mode ◽  
Good Agreement

<p>We theoretically investigate and optimize four-wave mixing (FWM) in silicon nitride (SiN) waveguides integrated with two-dimensional (2D) layered graphene oxide (GO) films. Based on extensive previous measurements of the material parameters of the GO films, we perform detailed analysis for the influence of device parameters including waveguide geometry, GO film thickness, length, and coating position on the FWM conversion efficiency (CE) and conversion bandwidth (CB). The influence of dispersion and photo-thermal changes in the GO films is also discussed. Owing to the strong mode overlap between the SiN waveguides and the highly nonlinear GO films, FWM in the hybrid waveguides can be significantly enhanced. We obtain good agreement with previous experimental results and show that by optimizing the device parameters to balance the trade-off between Kerr nonlinearity and loss, the FWM CE can be improved by as much as ~20.7 dB and the FWM CB can be increased by ~4.4 folds, relative to the uncoated waveguides. These results highlight the significantly enhanced FWM performance that can be achieved in SiN waveguides by integrating 2D layered GO films.<i></i></p>

Constitutive Model of Epoxy Resin Filled by Nano-Rubber Particles

2012 ◽  
Vol 557-559 ◽  
pp. 593-598
Author(s):  
Shao Kai Liao ◽  
Jing Nan Zhou
Keyword(s):  
Mechanical Properties ◽  
Constitutive Model ◽  
Epoxy Resin ◽  
Testing Machine ◽  
Low Frequency ◽  
Numerical Fitting ◽  
Static Tensile ◽  
Properties Of Materials ◽  
Parameter Values ◽  
Good Agreement

In the MTS testing machine, Quasi-static tensile mechanical testing is carried on to different Nano rubber epoxy, and have gained its mechanical properties; basing on the testing figures, ZWT constitutive model is used to descript the tensile mechanical properties of materials, and five parameter values are gained under low frequency of the model through numerical fitting; With the comparison of the test data , the numerical fitting result is in good agreement with test, at the same time, it also show that ZWT constitutive model can well descript the Quasi-static tensile mechanical properties of epoxy resin filled by nano-rubber.

Crushing and Flowing Characteristics of Lightweight Foamed Concrete under Different Loading Rates and Temperatures

2013 ◽  
Vol 535-536 ◽  
pp. 569-573
Author(s):  
Wei Guo Guo ◽  
Jian Jun Wang ◽  
Guang Liang Li ◽  
Ya Jie Shi
Keyword(s):  
Strain Rate ◽  
Testing Machine ◽  
Strain Rate Range ◽  
Deformation And Failure ◽  
Loading Rates ◽  
Electric Driving ◽  
Strength Based ◽  
Foamed Concrete ◽  
Three Stages ◽  
Good Agreement

Lightweight foamed concrete is one kind of new and important runway arresting materials for airplanes and other vehicles. To study its crushing and flowing behavior under different loading rates, an electric-driving screw testing machine, and an Instron VHS 8800 higher strain-rate testing machine are used. Crushing mechanical characteristics, and deformation and failure mode with the density of 0.20g/ccm are systematically analysed, while crushing strain-rate range from 0.001/s to about 102/s. Results show this foamed concrete suffers three stages of deformation during loading, namely elastic region, crushing plateau region and densification region; and it presents very low shear strength. Based on testing results, a phenomenological model is established, and comparing model predictions with experimental results, a good agreement is obtained.

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