Prediction of the spring-in of cylindrically orthotropic media and cross-ply laminates

The equation for prediction of the spring-in angle of a cylindrically orthotropic segment is shown to be independent of all material properties except for the anisotropic coefficients of thermal expansion and a stress-free state is insured for the corresponding unconstrained deformation. In contrast, the complete cylindrical geometry is shown to provide constraint to thermal deformation and thereby induce thermal residual stresses in the form of a moment. The method of superposition is demonstrated whereby traction-free conditions yield stress-free cylindrical elements with corresponding angular displacements at the element free boundaries. The first derivation of the spring-in equation is attributed to Radford, in contrast to the widely accepted view that the equation was first developed by Spencer et al. Finite-element methods, combined with the superposition approach, further validate the accuracy of the Radford equation for cylindrically orthotropic segments and explore its limitations for multiaxial composite laminates.

Calculating the gravity-free shape of sheet metal parts

This paper presents an iterative finite element (FE)–based method to calculate the gravity-free shape of nonrigid parts from an optical measurement performed on a non-over-constrained fixture. Measuring these kinds of parts in a stress-free state is almost impossible because deflections caused by their weight occur. To solve this problem, a simulation model of the measurement is created using available methods of reverse engineering. Then, an iterative algorithm calculates the gravity-free shape. The approach does not require a CAD model of the measured part, implying the whole part can be fully scanned. The application of this method mainly addresses thin, unstable sheet metal parts, like those commonly used in the automotive or aerospace industry. To show the performance of the proposed method, validations with simulation and experimental data are presented. The shown results meet the predefined quality goal to predict shapes within a tolerance of ± 0.05 mm measured in surface normal direction.

STUDY OF THE SHELF LIFE OF SEALANTS BASED ON LIQUID THIOKOL IN A STRESS-FREE STATE

The work carried out studies of the physicomechanical properties of polysulfide sealants of brands of U-30M and UT-31 after thermal, light aging, and the assessment of mushrooms. The data on the resistance of sealants of brands U-30M and UT-31 are investigated and summarized after the impact of accelerated climatic tests and aggressive environments. The optimal time and conditions for the storage of vulcanized sealants in the unattended state and components of sealants in warehouse conditions are determined, as well as the causes of different storage of sealing pastes based on liquid thiocola.

Non-dimensional thermoelastic model of a compound annular cylinder in a stress-free state with internal heat generation

A non-dimensional, axisymmetric, thermal-stress model for a three-layer cylinder with internal heating has been developed. Such a geometry is encountered in an annular target for isotope production. The middle cylinder is the heat generating source with an assumed thermal expansion coefficient that is smaller than that of the other two cylinders enclosing it. Hence, the development of the solution is based on the assumption that interfacial separation occurs at the interface of the middle cylinder and the outer cylinder, while contact is reinforced between the middle cylinder and the inner cylinder. The commercial finite element code Abaqus FEA is used to obtain a numerical model which is validated using the developed analytical solution. The non-dimensional analytical solution has been presented in a simplified, generalized form, and can be applied to either of the cylinders by adjusting a few parameters. The non-dimensional variable groupings allow physical insight into how the stresses and temperature distributions evolve. A detailed solution procedure along with a discussion of the results has been provided.

On the recovery of the stress-free configuration of the human cornea

Purpose: The geometries used to conduct numerical simulations of the biomechanics of the human cornea are reconstructed from images of the physiological configuration of the system, which is not in a stress-free state because of the interaction with the surrounding tissues. If the goal of the simulation is a realistic estimation of the mechanical engagement of the system, it is mandatory to obtain a stress-free configuration to which the external actions can be applied. Methods: Starting from a unique physiological image, the search of the stress-free configuration must be based on methods of inverse analysis. Inverse analysis assumes the knowledge of one or more geometrical configurations and, chosen a material model, obtains the optimal values of the material parameters that provide the numerical configurations closest to the physiological images. Given the multiplicity of available material models, the solution is not unique. Results: Three exemplary material models are used in this study to demonstrate that the obtained, non-unique, stress-free configuration is indeed strongly dependent on both material model and on material parameters. Conclusion: The likeliness of recovering the actual stress-free configuration of the human cornea can be improved by using and comparing two or more imaged configurations of the same cornea.

Modeling of subsurface ceramic inclusions in metallic matrices

All engineering materials have the potential to contain inhomogeneities that can act as initiators for fatigue cracks during cyclic loading. One class of inhomogeneity that can occur as a result of the processes used to create metallic materials is a ceramic inclusion, typically resulting from the raw material contamination during the melting process. This article examines the predicted behavior of hard ceramic inclusions in a nickel-base superalloy metallic matrix. Compressive residual stresses are created in the inclusion during cool down from a stress-free state at high temperature. The influence of the proximity of the inclusion to the surface of the matrix material is examined, together with the impact of subsequent uniaxial loading on the stress field in the inclusion and in the surrounding material. The stress field in the ceramic inclusion is observed to transition from compressive to tensile as a function of the proximity of the inclusion to the surface of the material and the applied uniaxial stress field. For deep subsurface inclusions, the uniaxial stress field required to achieve a tensile stress in the inclusion is close to the yield stress of the material. The sensitivity of this critical stress to material cyclic hardening behavior and to the temperature difference between the stress-free state and the operating state is also explored. The significance of these modeling results is discussed in terms of the sensitivity of nickel-base superalloys to crack formation and growth from ceramic inclusions and hence the impact on probabilistic fatigue life assessments of the presence, location and size of the ceramic inclusions.

A Modified Energy Method for Equilibrium Structure and Strain Energy of Armchair Single-Walled Carbon Nanotubes

Based on molecular mechanics, a modified energy model was proposed to study the angular variation and strain energy of armchair carbon nanotubes under stress-free conditions. In this model, the inversion energy term is added to make the calculation more accurate. The results show that the strain energy of armchair carbon nanotubes is more significantly affected by the added energy term under small diameter, especially when the diameter is less than 1 nm. This has a lot to do with the curvature of the tube. As compared with the unmodified model, the strain energy deviation between the two models decreases with the increase of tube diameter, which also verifies the remarkable characteristics of small diameter. At the same time, the angles change of armchair carbon nanotubes was calculated by using the modified model in the stress-free state, which is also quite different from that of the unmodified one in the small diameter.