Local Failure Modes and Critical Buckling Loads of a Meta-Functional Auxetic Sandwich Core for Composite Bridge Bearing Applications

This paper presents a novel meta-functional auxetic unit (MFAU) cell designed to improve performance and weight ratio for structural bridge bearing applications. Numerical investigations were conducted using three-dimensional finite element models validated by experimental results. The validated models were exposed to compression and buckling actions to identify structural failure modes, with special attention placed on the global behaviours of the meta-functional auxetic (MFA) composite bridge bearing. This bearing uses an unprecedented auxetic sandwich core design consisting of multiple MFAU cells. Numerical predictions of the elastic local critical buckling loads of the MFAU cell were in excellent agreement with both the analytical and experimental results, with an observed discrepancy of less than 1%. These results demonstrate that local buckling failures of MFAU cells can potentially be incurred prior to yielding under compression due to their slenderness ratios. Surprisingly, the designed sandwich core used in the MFA composite bridge bearing model can mimic an auxetic structure with significant crashworthiness, implying that this novel core composite structure can be tailored for structural bridge bearing applications. Parametric studies were thus carried out in order to enrich our insight into the MFA composite elements. These insights, stemming from both experimental and numerical studies, enable a novel design paradigm for MFAU that can significantly enhance the structural performance of MFA composite bridge bearings in practice.

STATISTICAL INVESTIGATION OF I-SHAPED STIFFENED RECTANGULAR PLATE BY TAGUCHI RESPONSE EVALUATION

In this research, the buckling of stiffened rectangular plate with square opening is studied using techniques of FEA. The stiffener used for analysis is I shaped placed on edges and in vertical configuration. Critical buckling loads are determined from load multiplier values obtained from FEA simulation. The features of stiffener are further optimized with Taguchi response technique to acquire essential responses of variables with respect to yield variables. The sensitivities of various optimization parameters are also determined. The results indicated that substantial enhancement in buckling resistance can be achieved through optimized dimensions of stiffeners. For safety-factor least both lower width and upper width shows positive sensitivities with lower width sensitivity rate is 54.041 (positive) and upper width rate is additionally 54.041 (positive). Hence, both upper width measurements and lower width has same impact on factor noticed for SPSW.

Advanced computational technique based on kriging and Polynomial Chaos Expansion for structural stability of mechanical systems with uncertainties

In this paper, a numerical strategy based on the combination of the kriging approach and the Polynomial Chaos Expansion (PCE) is proposed for the prediction of buckling loads due to random geometric imperfections and fluctuations in material properties of a mechanical system. The original computational approach is applied on a beam simply supported at both ends by rigid supports and by one punctual spring whose location and stiffness vary. The beam is subjected to a deterministic axial compression load. The PCE-kriging meta-modelling approach is employed to efficiently perform a parametric analysis with random geometrical and material properties. The approach proved to be computationally efficient in terms of number of model evaluations and in terms of computational time to predict accurately the buckling loads of a beam system. It is demonstrated that the buckling loads are substantially impacted not only by both the location and the stiffness of the spring, but also by the random parameters.

Stiffness compensation through matching buckling loads in a compliant four-bar mechanism

In this paper a novel alternative method of stiffness compensation in buckled mechanisms is investigated. This method involves the use of critical load matching, i.e. matching the first two buckling loads of a mechanism. An analytical simply supported four-bar linkage model consisting of three rigid links and four torsion springs in the joints is proposed for the analysis of this method. It is found that the first two buckling loads are exactly equal when the two outer springs are three times stiffer than the two inner springs. The force-deflection characteristic of this linkage architecture showed statically balanced behavior in both symmetric and asymmetric actuation. Using modal analysis, it was shown that the sum of the decomposed strain energy per buckling mode is constant throughout the motion range for this architecture. An equivalent lumped-compliant four-bar mechanism is designed; finite element and experimental analysis showed near zero actuation forces, verifying that critical load matching may be used to achieve significant stiffness compensation in buckled mechanisms.

Effect of Matching Buckling Loads on Post-Buckling Behavior in Compliant Mechanisms

In this paper, a novel method for stiffness compensation in compliant mechanisms is investigated. This method involves tuning the ratio between the first two critical buckling loads. To this end, the relative length and width of flexures in two architectures, a stepped beam and parallel guidance, are adjusted. Using finite element analysis, it is shown that by maximizing this ratio, the actuation force for transversal deflection in post-buckling is reduced. These results were validated experimentally by identifying the optimal designs in a given space and capturing the force-deflection characteristics of these mechanisms.

Effect of auxetic honeycomb angular stiffeners in cold-formed perforated and webbed steel upright section under buckling modes

This work was carried out on the buckling effects of cold-formed perforated steel columns with base auxetic polymer stiffeners. Buckling tests were carried out for three thicknesses of steel profiles (1.5–1.8 mm) with and without base stiffeners. Loading conditions were considered to be with displacement variation of 0.1 mm/s and respective axial loads and lateral displacements were noted. Results obtained states that the lateral displacement was found to be 2.2 for 1.8 mm CFS thickness and 93 kN of axial load with the use of auxetic stiffener with 14.8% of the variation in comparison without stiffener. The strain energy of absorption for auxetic stiffener is found to be high as 0.0523 at a lateral load of 80 kN for 1.8 mm CFS thickness. The maximum resistance to local, distortional, and Euler’s buckling loads was found to be high for 1.8 mm thick CFS with stiffener with 11.1%, 17.39%, and 10% in comparison without stiffener.

Nonlinear Buckling of Fixed Functionally Graded Material Arches Under a Locally Uniformly Distributed Radial Load

Functionally graded material (FGM) arches may be subjected to a locally radial load and have different material distributions leading to different nonlinear in-plane buckling behavior. Little studies is presented about effects of the type of material distributions on the nonlinear in-plane buckling of FGM arches under a locally radial load in the literature insofar. This paper focuses on investigating the nonlinear in-plane buckling behavior of fixed FGM arches under a locally uniformly distributed radial load and incorporating effects of the type of material distributions. New theoretical solutions for the limit point buckling load and bifurcation buckling loads and nonlinear equilibrium path of the fixed FGM arches under a locally uniformly distributed radial load that are subjected to three different types of material distributions are derived. The comparisons between theoretical and ANSYS results indicate that the theoretical solutions are accurate. In addition, the critical modified geometric slendernesses of FGM arches related to the switches of buckling modes are also derived. It is found that the type of material distributions of the fixed FGM arches affects the limit point buckling loads and bifurcation buckling loads as well as the nonlinear equilibrium path significantly. It is also found that the limit point buckling load and bifurcation buckling load increase with an increase of the modified geometric slenderness, the localized parameter and the proportional coefficient of homogeneous ceramic layer as well as a decrease of the power-law index p of material distributions of the FGM arches.

Buckling Design of Axially Compressed Cylindrical Shells Based on Energy Barrier Approach

Buckling design of axially compressed cylindrical shells is still a challenging subject considering the high imperfection-sensitive characteristic in this kind of structure. With the development of various design methods, the energy barrier concept dealing with buckling of imperfection-sensitive cylindrical shells exhibits a promising prospect in recent years. In this study, buckling design of imperfection-sensitive cylindrical shells under axial compression based on the energy barrier approach is systematically investigated. The methodology about buckling design based on the energy barrier approach is described in detail first taking advantage of the cylindrical shells whose buckling loads have been extensively tested. Then, validation and discussion about this buckling design method have been carried out by the numerical and experimental analyses on the cylindrical shells with different geometrical and boundary imperfections. Results in this study together with the available experimental data have verified the reliability and advantage of the buckling design method based on energy barrier approach. A design criterion based on the energy barrier approach is therefore established and compared with the other criteria. Results indicate that buckling design based on energy barrier approach can be used as an efficient way in the lightweight design of thin-shell structures.

Analysis of Critical Buckling Loads For Tool-Jointed Drillstrings in Deviated Wellbores

Excessive torque and drag, buckling and shear forces on downhole strings and tubulars are often encountered in the drilling of longer reach or deviational wells. Buckling of drillstring and BHA occurs in drillstring mainly due to high compressive forces. A point may be reached where these compressive forces rise and exceed the critical buckling loads leading to buckling of the drillstring/BHA or tubulars. This study focuses on the evaluation of the effect of tool-joint on the buckling of drillstrings for highly deviated wells. Tool-joint in pipes changes the pipes geometry in the wellbore thus affecting its hydraulics, orientation and stress distribution. A notable error will arise when straight pipe (with uniform outside diameter (OD) models are used to model pipes with end couplings and connections (such as tool joints). These errors may impact critical buckling loads, buckling initiation points, and post-buckling analysis of the pipe or BHA, thus affecting the success of drilling and completion operations. Torque and drag simulation and analysis was carried out for drillstring and BHA components in 9 5/8 in casing and 8.5 in open-hole sections to determine buckling loads. Two cases were considered; case 1 investigated the modeling and definition of buckling conditions for single straight body drillstrings and case 2 evaluated the buckling conditions for tool-jointed pipes. The result shows that buckling in tool-jointed pipes follows similar trend to that of straight body pipes with sinusoidal or lateral buckling being initiated first, and gradually progresses to helical buckling on increased axial force transfer. Furthermore, from the comparison of the results from two cases considered, it was observed that the presence tool-joint in the pipes led to a critical buckling load of 5.8% for sinusoidal buckling modes. The paper suggests that higher compressive force is needed to buckle the tool-jointed ends of the drillstring than the straight ends.

A Superconvergent Isogeometric Method with Refined Quadrature for Buckling Analysis of Thin Beams and Plates

A superconvergent isogeometric method is developed for the buckling analysis of thin beams and plates, in which the quadratic basis functions are particularly considered. This method is formulated through refining the quadrature rules used for the numerical integration of geometric and material stiffness matrices. The criterion for the quadrature refinement is the optimization of the buckling load accuracy under the assumption of harmonic buckling modes for thin beams and plates. The method development starts with the thin beam buckling analysis, where the material stiffness matrix with quadratic basis functions does not involve numerical integration and thus the refined quadrature rule for geometric stiffness matrix can be obtained in a relatively easy way. Subsequently, this refined quadrature rule for thin beam geometric stiffness matrix is conveniently generalized to the thin plate geometric stiffness matrix via the tensor product operation. Meanwhile, the refined quadrature rule for the thin plate material stiffness matrix is derived by minimizing the buckling load error. It turns out that the refined quadrature rule for the thin plate material stiffness matrix generally depends on the wave numbers of buckling modes. A theoretical error analysis for the buckling loads evinces that the isogeometric method with refined quadrature rules offers a fourth-order accurate superconvergent algorithm for buckling load computation, which is two orders higher than the standard isogeometric analysis approach. Numerical results well demonstrate the superconvergence of the proposed method for the buckling loads corresponding to harmonic buckling modes, and for those related with non-harmonic modes, the buckling loads given by the proposed method are also much more accurate than their counterparts produced by the conventional isogeometric analysis.