Buckling of a stiff thin film on an elastic graded compliant substrate

The buckling of a stiff film on a compliant substrate has attracted much attention due to its wide applications such as thin-film metrology, surface patterning and stretchable electronics. An analytical model is established for the buckling of a stiff thin film on a semi-infinite elastic graded compliant substrate subjected to in-plane compression. The critical compressive strain and buckling wavelength for the sinusoidal mode are obtained analytically for the case with the substrate modulus decaying exponentially. The rigorous finite element analysis (FEA) is performed to validate the analytical model and investigate the postbuckling behaviour of the system. The critical buckling strain for the period-doubling mode is obtained numerically. The influences of various material parameters on the results are investigated. These results are helpful to provide physical insights on the buckling of elastic graded substrate-supported thin film.

On the evaluation of plastic buckling of pipeline bending

In the present paper, various formulae for evaluating critical buckling strain of bending pipeline are analyzed on basis of its actual nature, available test data or finite element calculation results. The available test data is from different resources, it provides a more objective comparison; Especially, the experimental bending buckling data of Corona et al. and Kyriakides et al. for Al-6061-T6 aluminum pipes with various D/t value, as well as the prediction of Minnaar’s FEM regressive formula for high grade steel pipe are reanalyzed to check the reasonability of the plastically elliptical cross-section model. It shows that the consequence of the plastically elliptical cross-section model is more reasonable than others for the critical buckling strain prediction of a pipe bending in most cases.

Growth induced buckling instability of anisotropic tube and its application in wound edge instability

Fiber reinforced anisotropic material abounds in biological world. It has been demonstrated in previous theoretical and experimental works that growth of biological soft tubular tissue plays a significant role in morphogenesis and pathology. Here we investigate growth-induced buckling of anisotropic cylindrical tissue, focusing on the effects of type of growth(constraint/unconstraint, isotropic/anisotropic), fiber property(orientation, density and strength), geometry and any interaction between these factors. We studied one-layer and two-layer models and obtained a rich spectrum of results. For one-layer model, we demonstrate that circumferential fiber orientation has a consistent stabilizing effect under various scenarios of growth. Higher fiber density has a destabilizing effect by disabling high-mode buckling. For two-layer model, we found that critical buckling strain at inner boundary is an invariant under same isotropic growth rate ratio between inner/ outer layer(g1 /g0). Then we applied our model to wound healing and illustrate the effects of skin residual stress, fiber property, proliferation region width and wound size on the wound edge stability. We conclude that fiber-reinforcement is an important factor to consider when investigating growth induced instability of anisotropic soft tissue.

Power Law of Critical Buckling in Structural Members Supported by a Winkler Foundation

In the fields of engineering, nanoscience, and biomechanics, thin structural members, such as beams, plates, and shells, that are supported by an elastic medium are used in several applications. There is a possibility that these thin structures might buckle under severe loading conditions; higher-order, complicated elastic buckling modes can be found owing to the balance of rigidities between the thin members and elastic supports. In this study, we have shown a new and simple ‘power law’ relation between the critical buckling strain (or loads) and rigidity parameters in structural members supported by an elastic medium, which can be modelled as a Winkler foundation. The following structural members have been considered in this paper: i) a slender beam held by an outer elastic support under axial loading, ii) cylindrical shells supported by an inner elastic core under hydrostatic pressure (plane strain condition), and iii) complete spherical shells that are filled with an inner elastic medium.

Anisotropic Material Characterization and its Effect on Structural Integrity

In recent years anisotropic pipe material properties have gained more interest due to offshore; strain based design and fracture arrest topics. The effect of anisotropic UOE pipe material characteristic is analyzed in this contribution. Both, anisotropic strain dependent values (Lankford) and anisotropic strength dependent factors (Hill) are compared, and their impact on load bearing and plastic strain capacity is investigated. Several common load cases as internal and external pressure as well as bending are investigated. An analysis of the structural behavior concerning burst pressure and transverse strain capacity, collapse pressure, maximum bending moment and critical buckling strain is performed depending on yield strength variation. Therefore the above load and strain capacities are investigated based on present material anisotropy as well as numerical parametric studies. For the internal pressure as dominating load case, it was found that a higher yield strength in the longitudinal direction decreases burst pressure and increases transverse strain capacity. An increase of radial yield strength increases burst pressure as well as transverse strain capacity. For collapse applications, higher radial and transverse yield strength is beneficial as well as a lower longitudinal yield strength. Increasing longitudinal and radial yield strength leads to beneficial structural responses in terms of bending. Increase of transversal yield strength is thus not recommended as the maximum bending moment is not affected and critical buckling strain is decreased. Further it becomes clear from the above various parametric studies that the structural behavior is prone to differ for every set of distinct anisotropic parameters and the load cases. On the other hand selection of distinct anisotropic material can promote the desired structural behavior.

Buckling of Graphene Embedded in Polymer Matrix Under Compression

Understanding the mechanical behaviors of graphene under different stress states is crucial to their applications. Comparing with the bucking behavior of free standing graphene under compression, the monolayer graphene embedded in the polymer matrix has a higher critical buckling load and smaller atomic length scale wavelengths as well as buckling amplitudes. In this paper, the molecular dynamics (MD) method is adopted to study the buckling behaviors of embedded graphene under uniaxial compression. Two MD models are built, namely the hybrid MD/continuum nanomechanics model and the full MD model. Periodical boundary conditions are applied in the MD simulations. Graphene sheets with different aspect ratios are considered and it is observed that the critical buckling strain of graphene sheets embedded in polymer matrix is independent of their aspect ratios. The current simulation results match well with the reported experimental results. Furthermore, it is demonstrated that the current simulation method can produce clear buckling shapes, which are difficult to observe in nanoscale experiments.

An estimation of critical buckling strain for pipe subjected plastic bending

An approach for estimating critical buckling strain of pipe subjected plastic bending is established in the present paper. A rigid — perfectly plastic material model and cross section ovalization of pipe during bending are employed for the approach. The energy rates of the ovalised pipe bending and the cross section ovalising are proposed firstly. Furthermore, these energy rates are combined to perform the buckling analysis of pipe bending, an estimation formula of critical buckling strain for pipe subjected plastic bending is proposed. The predicting result of the new critical buckling strain formula is compared with the available experimental data, it shows that the formula is valid.

Beam-Mode Buckling of Buried Pipeline Subjected to Seismic Ground Motion

During seismic events, buried pipelines are subjected to deformation by seismic ground motion. In such cases, it is important to ensure the integrity of the pipeline. Both beam-mode and shell-mode buckling may occur in the event of compressive loading induced by seismic ground motion. In this study, the beam-mode buckling of a buried pipeline that occurred after the 2007 Niigataken Chuetsu-oki earthquake in Japan is investigated. A simple formula for estimating the critical buckling strain, which is the strain at the peak load, is derived, and the formula is validated by finite-element analysis. In the formula, the critical buckling strain increases with the pipeline diameter and hardness of the surrounding soil. By comparing the critical strain derived in this study for beam-mode buckling with the critical strain derived in a past study for shell-mode buckling, the formula facilitates the selection of the mode to be considered for evaluating the earthquake resistance of a pipeline. In addition to the critical buckling strain, a method to estimate the deformation caused by seismic ground motion is proposed; the method can be used to evaluate the earthquake resistance of buried pipelines. This method uses finite-element analyses, and the soil–pipe interaction is considered. This method is used to reproduce the actual beam-mode buckling observed after the Niigataken Chuetsu-oki earthquake, and the earthquake resistance of a buried pipeline with general properties is evaluated as an example.