Top-hat Cross-section Research Articles

Investigations Into the Stability of Thin-Walled Composite Structures with Top-Hat Cross-Sections

Abstract This paper presents a study of compressed thin-walled composite columns with an open cross-section. The tested specimens with a top-hat cross-section were made of CFRP material. Two arrangements of composite layers [0/-45/45/90]s and [90/0/90/0]s were compared. The paper focuses on the buckling phenomenon and the determination of the critical loads of the structure. It includes both numerical analyses using the finite element method (FEM) and validation on real specimens made using the autoclave technique. A comparison is made between the results obtained by both methods. The critical forces of the real specimens were determined using the P-wc3 approximation method. Both the evaluation of the buckling shape and the values of the critical forces showed a significant correlation between the experimental and numerical tests. This paper also compares the tested lay-ups.

Failure phenomenon of compressed thin-walled composite columns with top-hat cross-section for three laminate lay-ups

This paper presents an experimental and numerical study of the failure phenomenon of compressed composite top-hat (CFRP) columns with three different lay-up arrangements of the composite. The research was conducted both experimentally on physical structures and numerically based on advanced numerical models (based on the finite element method – ABAQUS® program). The research was conducted especially in the range of failure of thin-walled structures, with capturing the phenomena directly accompanying the loss of load-carrying capacity: damage initiation and evolution, as well as delamination. As part of the experimental study, the course of a time-shortening (universal testing machine) and acoustic emission signals were recorded (AMSY-5), allowing for an in-depth evaluation of the failure. Numerical simulations were conducted using independent failure models - progressive failure analysis (PFA) and cohesive zone model (CZM). This approach allowed for a comprehensive assessment of the failure phenomena, both in the context of the analysis of phenomena contributing to the loss of load-carrying capacity of the structure, as well as the delamination phenomenon. The main objective and novelty of this paper, was to compare the test results for three different composite lay-ups, in the context of failure studies. The research conducted in this paper on composite profiles with open sections, is a prelude to the research from the project from the National Science Centre (Poland) No. 2021/41/B/ST8/00148 on composite profiles with closed sections. In this paper, a preliminary methodology is presented for the realization of the research to be carried out on profiles with closed sections.

Failure study of compressed thin-walled composite columns with top-hat cross-section

This paper presents considerations on the failure of axially compressed thin-walled composite structures with open sections (using an top-hat section structure). The analyzed columns were made of composite material — carbon fiber reinforced polymer (CFRP) using the autoclave technique. The study was conducted in a comprehensive approach using both experimental methods and advanced numerical simulations based on the finite element method (in ABAQUS® program). Investigations were performed up to the total failure of the structure, while considering the phenomena directly contributing to the failure (damage initiation, damage evolution, delamination). During the conducted experimental studies, both the postbuckling equilibrium paths obtained from the universal testing machine and the acoustic emission signals were registered. Regarding the simultaneously conducted numerical simulations, two independent advanced damage models (progressive failure analysis — PFA and cohesive zone model — CZM) were used, allowing for a thorough analysis of the complex mechanism of the composite material failure phenomenon. Both numerical and experimental results show high agreement. This paper provides a more comprehensive understanding how failure occurs such that the design of the analyzed composite sections. The most important aspect of this paper is the potential to enable to understand the failure of the top-hat stiffeners during post buckling such that made it possible to utilize the stable, undamaged region of the post-buckling region. In addition, the paper conducts an advanced study based on the simultaneous use of two independent damage models, allowing in particular for a thorough analysis of the damage with delamination phenomenon detection, on structures with a complex shape of the end cross-sections of the structure.

Investigation of cold-formed steel open channel element under gravity loads

The specimen study consists of short, thin-walled columns made of cold-formed steel with an open top-hat cross-section. The walls in the specimens analyzed are made up of thin sheet component. Profiles were analyzed to classify the critical forces and post-critical stability paths. The ends of the column profile are considered to be supported. The numerical investigation was undertaken using the finite element method. The research includes an investigation of the post-critical stage of the profile on the different gravity loads of different thicknesses, depending on the eigenvalues of the profiles. The numerical simulation of the profiles is done using the ABAQUS® software. Based on a comparison of the outcomes of the profiles, an optimal profile is recommended for further analysis.

Failure analysis of thin-walled composite structures using independent advanced damage models

The aim of the study is to present a complex phenomenon of damage in thin-walled composite structures with an top-hat cross-section subjected to axial compression. Actual structures were prepared using the auto-clave technique (CFRP composite). Research was conducted in a full range of load – until construction damage. In the case of experimental testing both post-critical equilibrium paths and acoustic emission signals were recorded. Numerical simulations were realised using progressive fracture analysis (PFA) and cohesive zone model (CZM). Such approach allowed one to assess the loss of load capacity along with demonstrating the delamination phenomenon. A measurable effect of the experimental-numerical research was presenting the influence of axial compression on post-critical behaviour of the structure and damage phases.

Experimental-numerical study into the stability and failure of compressed thin-walled composite profiles using progressive failure analysis and cohesive zone model

This study investigates the stability and failure of thin-walled composite structures with a top-hat cross section under axial compressive loading. The tested profiles were made of CFRP composite material by autoclaving. The scope of the research included experimental tests of real samples and numerical analysis by the finite element method using the ABAQUS® program. Both experimental tests and numerical analysis were performed over the full range of loading until structural failure. In experiments, postbuckling equilibrium paths and acoustic emission signals were measured, which allowed a comprehensive analysis of failure for the composite material. Numerical calculations were performed by progressive failure analysis, considering the failure initiation criteria under Hashin’s theory and failure evolution based on the energy criterion. Additionally, the cohesive zone model (CZM) was used to simulate delamination. Numerical results and experimental findings show high agreement. Moreover, the results reveal an interesting relationship between the compressive load and the buckling, postbuckling and failure of the analyzed structures.

Progressive Failure Analysis of Thin-Walled Composite Structures Verified Experimentally.

The subject of the presented research was a thin-walled composite column made of CFRP (carbon-epoxy laminate). The test sample had a top-hat cross-section with a symmetrical arrangement of laminate layers [90/−45/45/0]s. The composite structure was subjected to the process of axial compression. Experimental and numerical tests for the loss of stability and load-carrying capacity of the composite construction were carried out. The numerical buckling analysis was carried out based on the minimum potential energy criterion (based on the solution of an eigenvalue problem). The study of loss of load-carrying capacity was performed on the basis of a progressive failure analysis, solving the problem of non-linear stability based on Newton-Raphson’s incremental iterative method. Numerical results of critical and post-critical state were confronted with experimental research in order to estimate the vulnerable areas of the structure, showing areas prone to damage of the material.

Buckling and limit states of thin-walled composite columns under eccentric load

Abstract The objective of this study was to investigate the influence of eccentric compressive load on the buckling, post-buckling and load-carrying capacity of thin-walled top-hat cross-section composite columns. The CFRP columns were manufactured by the autoclave technique. The scope of the study involved performing experimental tests on real structures as well as numerical calculations by the finite element method. The experimental tests were conducted in the full range of loading, until the structure's failure. Post-buckling equilibrium paths and acoustic emission signals were measured in order to determine actual condition of the composite material. Nonlinear FEM calculations were made by the progressive damage criterion, in which the damage initiation of the composite material was estimated based on Hashin's theory, whereas damage evolution was described by the energy criterion. The numerical simulations were performed using the commercial software ABAQUS®. The numerical results were in good agreement with the experimental results obtained for real structures. The results demonstrated a significant influence of eccentric compressive load on the buckling and post-buckling characteristics of the tested structures.

The Fe Analysis and Variation of Composite Top Hat Shaped Beam

Abstract The main goal of this work is to provide a composite alternative to an already existing beam which has top hat cross section. The main part of this work is focused on using the finite element method to solve the problem. Firstly, a duralumin version will be used to calibrate the computation, then the problem will be solved for different options of slightly adjusted geometry. The computation itself will include general static analysis as well as analysis of buckling.

Numerical and experimental analysis of stability of thin-walled composite structures subjected to eccentric load

The study investigates the effect of eccentric load on the stability and post-critical states of thin-walled composite top-hat cross-section columns made of CFRP under compression. The specimens were subjected to compressive load on the universal testing machine Zwick Z100 with regard to both axial and eccentric compressive loads. On the basis of the experimental studies, numerical models of thin-walled composite profiles were designed and verified by numerical analysis based on the FEM. The first stage of the conducted studies was performing a linear buckling analysis of stability of composite structures. The second stage of the analysis involved performing a nonlinear analysis of the thin-walled structures with geometric imperfections reflecting the lowest buckling modes. The obtained test results showed various effects of non-axial compressive load on the critical load values and stiffness of the construction in the post-critical state. In the case of eccentric loading in the direction parallel to the web of the top-hat profiles, the critical load values practically did not change – a drop in the force did not exceed 1.5%, as well as there was no change in the stiffness of the structure in the post-critical state. The realization of the eccentricity in the direction perpendicular to the profile web caused a drop in the critical force equal 43% and a significant decrease in the stiffness of the structure. On the other hand, implementation of the eccentricity load toward the web caused an increase in the critical force by more than 20%, despite very small eccentricity values of only 4mm were applied. This proved high sensitivity of the tested structures to the non-axial load in the direction perpendicular to the web of the profile. The FEM results and the experimental findings showed satisfactory agreement.

Numerical and experimental failure analysis of thin-walled composite columns with a top-hat cross section under axial compression

The paper describes a numerical and experimental study investigating the load carrying capacity of thin-walled composite columns with a top-hat cross section under axial compression. The tested columns were made of carbon-epoxy laminate with symmetrical lay-up and ply orientation [0/90/0/90]s. The experiments were performed on a universal testing machine, Zwick Z100, under full load conditions until total failure of the structure. In the experiments, post-critical equilibrium paths of the structure were determined, defining the relationship between compressive force and deflection and enabling the validation of the numerical models. Based on the obtained post-critical equilibrium paths, the critical load of the structure was determined by approximation methods. Simultaneously, a numerical analysis was performed by the finite element method using the Abaqus® software. The critical state was determined via a linear eigenvalue analysis, and the critical load and a corresponding buckling mode were estimated. The next stage of the numerical analysis involved solving a nonlinear stability problem for a structure with initialized geometric imperfection reflecting the lowest buckling mode. The geometrically non-linear problem was solved by the Newton-Raphson method. The load carrying capacity of the composite structure in the post-buckling state was determined by the progressive failure criterion which estimates damage initiation in the composite material based on the Hashin criterion, while the progression of damage is described with the energy criterion describing the degradation of stiffness of finite elements. The numerical and experimental results show high agreement, which confirms the adequacy of the developed numerical models of composite structures. Results presented in the paper are part of a study conducted under the project no. UMO-2015/19/B/ST8/02800 financed by the National Science Centre Poland.

Forming of an axially tailored automotive channel section through hot stamping of tailor-welded blanks

In this work, top-hat cross-section axial crush rail specimens with tailored properties along their length were investigated. These top-hat channels were hot stamped in a fully cooled die set from tailor-welded blanks (TWBs). The blanks were laser-welded and comprised Usibor® 1500-AS joined to Ductibor® 500-AS in 1.2 mm and 1.6 mm thicknesses. Micro-hardness measurements were taken along the length of the formed specimens to map the hardness profile along their length. The effect of gauge thickness on hardness was evaluated. The hardness profile of these TWB parts was compared to that of parts formed using tailored in-die heating (IDH).

Experimental-numerical test of open section composite columns stability subjected to axial compression

Purpose: The aim of the work was to analyse the critical state of thin-walled composite profiles with top-hat cross section under axial compression. Design/methodology/approach: The purpose of the work was achieved by using known approximation methods in experimental and finite element methods for numerical simulations. The scope of work included an analysis of the behavior of thin-walled composite structures in critical state with respect to numerical studies verified experimentally. Findings: In the presented work were determined the values of critical loads related to the loss of stability of the structures by using well-known approximation methods and computer simulations (FEM analysis). Research limitations/implications: The research presented in the paper is about the potential possibility of determining the values of critical loads equivalent to loss of stability of thin-walled composite structures and the future possibility of analyzing limit states related to loss of load capacity. Practical implications: The practical approach in the actual application of the described specimen and methodology of study is related to the necessity of carrying out of strength analyzes, allowing for a precise assessment of the loads upon which the loss of stability (bifurcation) occurs. Originality/value: The originality of the research is closely associated with used the thinwalled composite profile with top-hat cross-section, which is commonly used in the fuselage of passenger airplane. The methodology of simultaneous confrontation of the obtained results of critical loads by using approximation methods and using the linear eigenvalue solution in numerical analysis demonstrates the originality of the research character. Presented results and the methodology are intended for researchers, who are concerned with the topic of loss of stability of thin-walled composite structures.

Experimental and Numerical Study of the Buckling of Composite Profiles with Open Cross Section under Axial Compression

The object of the research are short, thin-walled columns with an open top-hat cross section made of multilayer laminate. The walls of the investigated profiles are made of plate elements. The entire columns are subjected to uniform compression. A detailed analysis allowed us to determine critical forces and post-critical equilibrium paths. It is assumed that the columns are articulately supported on the edges forming their ends. The numerical investigation is performed by the finite element method. The study involves solving the problem of eigenvalue and the non-linear problem of stability of the structure. The numerical analysis is performed by the commercial simulation software ABAQUS®. The numerical results are then validated experimentally. In the discussed cases, it is assumed that the material operates within a linearly-elastic range, and the non-linearity of the FEM model is due to large displacements.

Load carrying capacity of functionally graded columns with open cross-sections under static compression

The nonlinear problems of static interactive buckling of thin-walled columns with a top hat cross-section and a lip channel cross-section, which are made of functionally graded materials (FGMs), are considered. The FG structures are subjected to static compression. The effect of temperature is neglected. It is assumed that functionally graded materials are subject to Hooke’s law. An interaction of different modes has been analyzed in detail. Numerous different combinations of buckling modes have been computed. In all cases the theoretical value of load carrying capacity has been determined.In order to obtain the equilibrium equations of thin-walled structures from Hamilton’s Principle for the asymptotic analytical–numerical method. The classical laminate plate theory (CLPT) which has been modified in such a way that it additionally accounts for the full Green’s strain tensor and the second Pioli–Kirchhoff’s stress tensor has been applied. The study is based on the numerical method of the transition matrix using Godunov’s orthogonalization. Distortions of cross-sections and a shear-lag phenomenon are examined. This paper is a continuation of the study described in the work of the authors entitled: “Static interactive buckling of functionally graded columns with closed cross-sections subjected to axial compression” Composite Structures 123, 2015, 257–262.