scholarly journals Thermal Prestress in Composite Compliant Shell Mechanisms

2018 ◽  
Author(s):  
Jonathan P. Stacey ◽  
Matthew P. O’Donnell ◽  
Mark Schenk
Keyword(s):  
Thermal Effects ◽  
Compliant Mechanisms ◽  
Large Angle ◽  
Torsional Stiffness ◽  
Internal Stresses ◽  
Structural Behaviour ◽  
Thermally Induced ◽  
Composite Tape ◽  
Out Of Plane ◽  
Good Agreement

Due to the anisotropic nature of fibre-reinforced laminates, thermally-induced internal stresses can remain in the material after manufacture. Mismatches between coefficients of thermal expansion are especially prominent in thin shells with fewer plies or large angle variations. Such stresses cause out-of-plane warping and are therefore often deliberately avoided. Utilising their effects on structural behaviour however, can enable stiffness-tailored composite compliant mechanisms. Work detailed in this paper aims to exploit thermal prestress to reduce the torsional stiffness of cross-ply tape laminate springs. An extension of an analytical tape spring model with composite thermal analysis is presented, which shows that thermal effects cause significant changes to the energy landscapes of thin composite shells. Tape springs that would otherwise be monostable structures become bistable and exhibit greater ranges of low-energy twisting when thermally-induced prestress is present. Predicted shell geometries are compared with finite element models and manufactured samples, showing good agreement between all approaches. The limited feasibility of zero torsional stiffness composite tape springs is discussed, as well as wider challenges involved in manufacturing prestressed composite compliant mechanisms such as fibre misalignment and moisture ingress.

scholarly journals Study on the large-displacement behaviour of a spiral spring with variations of cross-section, orthotropy and prestress

2018 ◽  
Vol 9 (2) ◽  
pp. 337-348 ◽  
Author(s):  
Giuseppe Radaelli ◽  
Just L. Herder
Keyword(s):  
Graphical Representation ◽  
Compliant Mechanisms ◽  
Large Displacement ◽  
Torsional Stiffness ◽  
Nonlinear Behaviour ◽  
Cross Sectional ◽  
Energy Field ◽  
Spiral Spring ◽  
Out Of Plane ◽  
Torsion Stiffness

Abstract. This work is dedicated to the study of the large-displacement behaviour of a spiral spring. Parameters that influence the local torsion stiffness of the beam that constitutes the spiral are varied and their effect is studied. Cross-sectional shape, orthotropic material orientation and prestress are the three classes of parameters that are varied. The effect that the local change in torsional stiffness has on the overall behaviour is illustrated in a linearised way by comparing in-plane and out-of-plane stiffnesses, and nonlinearly, by inspecting a graphical representation of the potential energy field of the system. Several embodiments composed of multiple spirals are showed to illustrate how the understanding of the nonlinear behaviour could be exploited in conceptual design of compliant mechanisms.

scholarly journals Mitigation of Thermal Effects in End Pumping of Nd : YAG and Composite YAG/Nd : YAG Laser Crystas, Modelling and Experiments-=SUP=-1-=/SUP=-

2021 ◽  
Vol 91 (8) ◽  
pp. 1268
Author(s):  
N.M. Al-Hosiny ◽  
A.A. El-Maaref ◽  
R.M. El-Agmy
Keyword(s):  
Stress Intensity ◽  
Thermal Effects ◽  
Focal Length ◽  
Solid State Lasers ◽  
Yag Laser ◽  
Thermally Induced ◽  
Yag Lasers ◽  
Thermal Focal Length ◽  
Composite Laser ◽  
Good Agreement

In this work, we have presented a finite element (FE) numerical modelling simulations to study and analyze the thermal effects in Nd : YAG and composite YAG/Nd : YAG laser rods. We have calculated the temperature distributions, stress intensity and thermal focal lengths at different pump powers for both rods. The FE simulations showed that using composite laser rod of undoped cap reduces the maximum value of stress intensity and thermal focal length by ~35% and ~ 50%, respectively. We have verified the FE calculations experimentally by direct measurement of focal length of thermally induced lens by using Hartmann-Shack wavefront sensor. Good agreement was obtained between FE calculations and experimental measurements. Keywords: Nd : YAG lasers, Thermal lens, Wavefront sensing, solid state lasers.

scholarly journals Thermal Prestress in Composite Compliant Shell Mechanisms

2019 ◽  
Vol 11 (2) ◽  
Author(s):  
Jonathan P. Stacey ◽  
Matthew P. O'Donnell ◽  
Mark Schenk
Keyword(s):  
Mechanical Properties ◽  
Thermal Analysis ◽  
Finite Element ◽  
Composite Laminate ◽  
Compliant Mechanisms ◽  
Low Energy ◽  
Spring Model ◽  
Energy Landscapes ◽  
Thermally Induced ◽  
Good Agreement

This paper explores the ability to tailor the mechanical properties of composite compliant shell mechanisms, by exploiting the thermal prestress introduced during the composite laminate cure. An extension of an analytical tape spring model with composite thermal analysis is presented, and the effect of the thermal prestress is studied by means of energy landscapes for the cylindrical composite shells. Tape springs that would otherwise be monostable structures become bistable and exhibit greater ranges of low-energy twisting with thermally induced prestress. Predicted shell geometries are compared with finite element (FE) results and manufactured samples, showing good agreement between all approaches. Wider challenges around the manufacture of prestressed composite compliant mechanisms are discussed.

Efficient Fatigue Testing of Tubular Joints

2015 ◽  
Author(s):  
P. Thibaux ◽  
J. Van Wittenberghe ◽  
E. Van Pottelberg ◽  
M. Van Poucke ◽  
P. De Baets ◽  
...  
Keyword(s):  
Finite Element ◽  
Fatigue Testing ◽  
Fatigue Loading ◽  
Tubular Joints ◽  
Testing Method ◽  
Out Of Plane ◽  
Resonance Principle ◽  
Tubular Joint ◽  
The Cost ◽  
Good Agreement

Tubular joints are intensively used in off-shore structures for shallow waters. Depending on the sea conditions and the type of structure, the design can be fatigue driven. This is particularly the case for off-shore wind turbines, where turbulences are generating a fatigue loading. Any improvement of the fatigue performance of the tubular joint would be beneficial to reduce the weight and the cost of the structure. To assess efficiently the fatigue resistance of the tubular joint, a testing method has been developed based on the resonance principle. The complete circumference of the welded joint can be loaded, successively in the in-plane and out-of-plane modes at a frequency close to 20Hz. Finite element computations were used to investigate the feasibility of the concept. Then, an X-node was made and successfully tested to investigate the stress distribution along the weld. The experimental results were compared with finite element computations, giving a good agreement.

scholarly journals Out-of-Plane Vibration of Curved Uniform and Tapered Beams with Additional Mass

2017 ◽  
Vol 2017 ◽  
pp. 1-8 ◽  
Author(s):  
Hamdi Alper Özyiğit ◽  
Mehmet Yetmez ◽  
Utku Uzun
Keyword(s):  
Finite Element ◽  
Free Vibration ◽  
Boundary Conditions ◽  
Natural Frequencies ◽  
Variable Cross ◽  
Additional Mass ◽  
Inertia Effects ◽  
Tapered Beam ◽  
Out Of Plane ◽  
Good Agreement

As there is a gap in literature about out-of-plane vibrations of curved and variable cross-sectioned beams, the aim of this study is to analyze the free out-of-plane vibrations of curved beams which are symmetrically and nonsymmetrically tapered. Out-of-plane free vibration of curved uniform and tapered beams with additional mass is also investigated. Finite element method is used for all analyses. Curvature type is assumed to be circular. For the different boundary conditions, natural frequencies of both symmetrical and unsymmetrical tapered beams are given together with that of uniform tapered beam. Bending, torsional, and rotary inertia effects are considered with respect to no-shear effect. Variations of natural frequencies with additional mass and the mass location are examined. Results are given in tabular form. It is concluded that (i) for the uniform tapered beam there is a good agreement between the results of this study and that of literature and (ii) for the symmetrical curved tapered beam there is also a good agreement between the results of this study and that of a finite element model by using MSC.Marc. Results of out-of-plane free vibration of symmetrically tapered beams for specified boundary conditions are addressed.

Computer studies of fast ion trajectories in crystals

1968 ◽  
Vol 46 (6) ◽  
pp. 503-516 ◽  
Author(s):  
D. V. Morgan ◽  
D. van Vliet
Keyword(s):  
Large Angle ◽  
Classical Dynamics ◽  
Perfect Lattice ◽  
Fast Ions ◽  
Angle Scattering ◽  
Initial Work ◽  
Fast Ion ◽  
Thermal Vibrations ◽  
Computer Studies ◽  
Good Agreement

A computer program has been developed which follows the trajectories of fast ions in crystals, based on the assumption of classical dynamics and binary collisions. Initial work has been directed at various aspects of proton channeling in copper in the energy range 5–500 keV. The critical angle and distance of closest approach in a perfect lattice have been evaluated for both rows and planes and compare well with the predictions of the continuum model as developed by Lindhard (1965). We also discuss the overlap of close-packed rows and planes, and the modifications necessary to the basic theory when thermal vibrations are introduced. Experiments have been simulated directly by obtaining a statistical analysis of the velocity distribution of protons reflected from a (100) face of copper and transmitted through a thin (~1800 Â) crystal. In reflection, distinct minima were obtained along directions corresponding to close-packed rows and planes, in good agreement with experimental "blocking patterns" (Nelson 1967a). Transmission patterns also revealed a lack of large-angle scattering parallel to close-packed planes, analogous to the white arms observed experimentally with thinner crystals.

scholarly journals Fundamental principles of structural behaviour under thermal effects

2001 ◽  
Vol 36 (8) ◽  
pp. 721-744 ◽  
Author(s):  
A.S. Usmani ◽  
J.M. Rotter ◽  
S. Lamont ◽  
A.M. Sanad ◽  
M. Gillie
Keyword(s):  
Thermal Effects ◽  
Structural Behaviour

Structural Properties Of Co/Re Superlattices

1991 ◽  
Vol 238 ◽  
Author(s):  
Y. Huai ◽  
R. W. Cochrane ◽  
Y. Shi ◽  
H. E. Fischer ◽  
M. Sutton
Keyword(s):  
Structural Disorder ◽  
Multilayer Films ◽  
Film Plane ◽  
X Ray Diffraction ◽  
X Ray ◽  
Bilayer Films ◽  
Out Of Plane ◽  
Reflectivity Data ◽  
Sharp Interfaces ◽  
Good Agreement

ABSTRACTThe structures of equal-thickness Co/Re multilayer films and several Co/Re bilayer films have been investigated by X-ray diffraction at low and high angles. Analysis of low-angle reflectivity data from bilayer films indicates that interfacial intermixing is limited to three monolayers and that the two interfacial configurations are different. The high-angle X-ray diffraction data show that multilayer films have coherent interfaces and a highly textured structure with hep [002] orientations normal to the film plane for periods 21 Å ≤ Λ ≤220 Å. Detailed structures have been determined by fitting the X-ray spectra to calculated ones using a trapezoidal model. The results indicate that samples with 42 Å≤ Λ ≤220 Å have relatively sharp interfaces, in good agreement with the bilayer results. In addition, an out-of-plane expansion of the Co (002) layer is observed in samples with large Λ and results from structural disorder leading to a reduced atomic density. For Λ <21 Å the interfaces arise from the rougher surfaces of the deposited layers.

The Effect of Stitching on Compression Behavior of Stiffened Composite Panels

2001 ◽  
Author(s):  
Sung S. Suh ◽  
H. Thomas Hahn ◽  
Nanlin Han ◽  
Jenn-Ming Yang
Keyword(s):  
Beneficial Effect ◽  
Compression Behavior ◽  
Stiffened Panels ◽  
Shell Elements ◽  
Stitch Density ◽  
Stiffened Composite Panels ◽  
Out Of Plane ◽  
Post Buckling ◽  
Post Impact ◽  
Good Agreement

Abstract Failure of stiffened panels under compression is preceded by buckling of their skin and hence is affected by the presence of out-of-plane stresses. One of the promising methods of preventing premature delamination is stitching. The present paper discusses the effect of such stitching on compression behavior of blade-stiffened panels that were fabricated from plain weave AS4/3501-6 through resin film infusion process. Kevlar 29 yarn was used at a stitch density of 9.92 stitches per cm2. Some of the panels were damaged by drop-weight impact before compression testing. For comparison purposes unstitched panels with the same materials and dimensions were also tested under the same loading conditions. Stitching resulted in a 10% improvement in strength in the absence of any intentional damage. The beneficial effect of stitching was most obvious when the panels were impacted on a flange: a 50% improvement was observed in post-impact strength. However, stitching could not prevent stiffener from failure when impacted directly. Thus stitching had no beneficial effect when impact occurred on a stiffener. A buckling and post-buckling analysis was carried out using 3-D shell elements on the Abaqus. Predictions were in fairly good agreement with the experimental data.

Torsional Stiffness of a Thin-Walled Beam Braced by Pinned or Rigidly Fixed Transverse Diaphragms

1973 ◽  
Vol 15 (5) ◽  
pp. 351-356
Author(s):  
T. Harrison ◽  
J. M. Siddall
Keyword(s):  
Experimental Evidence ◽  
Theoretical Work ◽  
Torsional Stiffness ◽  
Cross Sectional ◽  
Cross Sectional Profile ◽  
Thin Walled ◽  
Sectional Profile ◽  
Good Agreement

The torsional stiffness of a thin-walled beam of open cross-sectional profile braced by evenly spaced transverse diaphragms is studied. Diaphragms rigidly fixed or attached by frictionless pins are treated and it is seen that, in either case, the only effect is to modify the St Venant torsional constant for the thin-walled beam. The theoretical work is supported by experimental evidence from two braced perspex channels which simulate the two assumed methods of attaching the diaphragms. Good agreement is demonstrated.

Sign in / Sign up

Export Citation Format

Share Document