[pt] Há um interesse crescente na aplicação de vigas e colunas de paredes finas de materiais compostos em vários campos da engenharia. No entanto, pouco se sabe sobre seu comportamento não linear local e global sob cargas estáticas e dinâmicas. Aqui se apresenta a análise local e global de um perfil com seção canal de polímero reforçado com fibras. Na análise global, as equações não lineares de movimento da coluna de parede fina são derivadas em termos dos dois deslocamentos de flexão e do ângulo de torção, levando em consideração grandes deslocamentos, efeitos de empenamento e encurtamento. As equações de movimento não lineares governantes são discretizadas no espaço usando o método de Galerkin. Para a análise local, a seção do canal é discretizada em três placas, que são modeladas usando duas teorias não lineares de placas: a teoria clássica e a teoria de deformação por cisalhamento de primeira ordem. O sistema contínuo é discretizado usando o método de Ritz. Inicialmente são determinados analiticamente, através da resolução dos respectivos problemas de autovalor, a carga e modo crítico, as frequências naturais de vibração, bem como a relação carga-frequência do perfil em função da sua geometria e das propriedades do material. A seguir são obtidos, usando o método de Newton-Raphson e técnicas de continuação, os caminhos pós-críticos da estrutura perfeita e os caminhos não lineares de equilíbrio da estrutura imperfeita e investiga-se a sensibilidade a imperfeições, considerando diversos tipos de imperfeições geométricas. Finalmente, investigam-se as oscilações não lineares e a instabilidade paramétrica da coluna sob cargas axiais harmônicas. As equações de movimento não lineares são resolvidas numericamente pelo método de Runge-Kutta de quarta ordem. As regiões de instabilidade paramétrica são determinadas como uma função dos parâmetros do material ortotrópico, amortecimento e geometria da seção transversal. Os diagramas de bifurcação são obtidos empregando técnicas de continuação e o método da força bruta, e a estabilidade das soluções é posteriormente investigada usando a teoria de Floquet. A análise de bifurcação permite a identificação das bifurcações associadas às fronteiras de instabilidade paramétrica, bem como a existência de soluções coexistentes. Em seguida, a evolução das bacias de atração das soluções coexistentes em função da magnitude da excitação é investigada, a fim de avaliar a integridade dinâmica das soluções. Os resultados demonstram que a coluna pode perder estabilidade em níveis de carga bem abaixo da carga de flambagem estática e, portanto, o projetista deve ter cuidado ao lidar com essas estruturas sujeitas a cargas axiais variáveis no tempo. / [en] The continuous system is discretized using the Ritz method. Initially, the load and critical mode of the profile, its natural frequencies, as well as the load-frequency relation are determined analytically as a function of the column geometry and material properties by solving the respective eigenvalue problems. Next, using the Newton-Raphson method and continuation techniques, the post-critical paths of the perfect structure and the non-linear equilibrium paths of the imperfect structure are obtained and the imperfection sensitivity is investigated, considering several types of geometric imperfections. Finally, the nonlinear oscillations and parametric instability of the column under harmonic axial loads are investigated. Non-linear equations of motion are solved numerically by the fourth-order Runge-Kutta method. The regions of parametric instability are determined as a function of the parameters of the orthotropic material, damping ratio and cross-sectional geometry. The bifurcation diagrams are obtained using continuation techniques and the brute force method, and the stability of the solutions is further investigated using Floquet s theory. The bifurcation analysis allows the identification of the bifurcations associated with the boundaries of parametric instability, as well as the existence of coexisting solutions. Then, the evolution of the basins of attraction of the coexisting solutions as a function of the forcing magnitude is investigated, in order to evaluate the dynamic integrity of the solutions. The results demonstrate that the column can lose stability at load levels well below the static buckling load and, therefore, the designer must be careful when dealing with these structures subject to time-varying axial loads.

Das Innenhochdruck-Umformen (IHU), ein Verfahren der Metallformung zur Herstellung von anspruchsvollen Bauteilen mit komplexer Geometrie aus meist hohlzylindrischen Halbzeugen, wird in einigen Branchen seit mehreren Jahrzehnten mit großem Erfolg angewendet. Insbesondere die vielfältigen Applikationen aus dem Automotivbereich wie z.B. Elemente der Abgasanlage, Strukturbauteile oder auch Antriebselemente können hergestellt werden. Da die Trends der Rohr- und Blechumformung in Richtung Leichtbau, komplexer Bauteile mit geringen Ausbringungsmengen und hoher Genauigkeit gehen, ist perspektivisch mit der Erschließung weiterer Anwendungs-gebiete zu rechnen. Um das Verfahren effizienter zu gestalten, können zusätzliche Prozesse in das IHU-Verfahren integriert werden. Beispiele dafür sind das Lochen sowie das Kragenziehen und weitere Fügeprozesse. Typische Bauteile sind Leicht-baunockenwellen, bei denen die Nocken innerhalb des Umformprozesses auf die Rohre form- und kraftschlüssig gefügt werden. Ungeachtet einer beliebigen dreidimensionalen Formgebung und der hohen Flexibilität unterliegt das IHU-Verfahren gewissen Restriktionen. So werden im industriellen Umfeld generell nur Halbzeuge mit Wanddicken ab 1,5 mm bis maximal 3,5 mm umgeformt. Bei dünnwandigen, rohr-förmigen Bauteilen sind Wanddicken unter 1 mm üblich. Diese erfordern spezielle technologische Maßnahmen im Bereich des Werkzeugbaus insbesondere Anforderungen an Dichtsystem sowie Werkzeuggravur und unterliegen Prozessparametern mit entsprechend kleineren Prozessfenstern.

Hydroforming, a metal forming process for the production of sophisticated components with complex geometries from mostly tubular semi-finished products, has been successfully applied in some industries for several decades. Particularly, various applications from the automotive sector such as elements of the exhaust system, structural components or drive elements can be manufactured. As trends in tube and sheet metal forming move towards lightweight construction, complex components with low production volumes, and high precision, the prospective expansion into further application areas is anticipated. To enhance the efficiency of the process, additional processes can be integrated into the hydroforming process. Examples of this are punching, collar pulling and other joining processes. Typical components include lightweight camshafts in which the cams are form- and force-fitted onto the tubes within forming process. Despite arbitrary three-dimensional forming and the high degree of flexibility, the hydroforming process is subjected to certain restrictions. Generally, in an industrial environment, only semi-finished products with wall thicknesses from 1.5 mm to a maximum of 3.5 mm are formed. Wall thicknesses of less than 1 mm are common for thin-walled, tubular components. These require special technological measures in the area of toolmaking, particularly regarding sealing system and tool engraving, and are subjected to process parameters with correspondingly smaller process windows

No description available.

The aging infrastructure worldwide and the typical increase in service loads relative to original design loads make it essential to develop effective techniques for strengthening and rehabilitating existing structures, to enhance their resistance. An effective method for strengthening existing steel I-beams is to weld either one or two cover plates to the flange(s). In many cases, it is not feasible to completely unload the beam before carrying out the strengthening procedure. In these conditions, operators resort to strengthen beams while under loading. In such scenarios, it becomes a challenging task to assess the lateral torsional buckling (LTB) capacity of the member under present steel design standards (e.g., CAN/CSA-S16 2019 and ANSI/AISC360 2022) which do not consider the effect of pre-strengthening loads on LTB resistance. Within this context, the present study investigates the effects of pre-strengthening loads on the critical moment capacity by developing a series of solutions, ranging from elaborate and accurate to simplified but approximate, to predict the elastic LTB capacity of beams strengthened with cover plate(s) while under load. In this respect, the study contributes to the existing body of knowledge through four aspects: In the first contribution, a shell-based finite element (FE) study is developed to analyze the effect of various geometric and loading parameters on the LTB capacity of doubly symmetric beams strengthened symmetrically with two cover plates. The study carefully simulates the entire history, including the application of pre-existing loads, clamping forces to align the initially straight steel cover plates with the bent beam configuration, the rebound effect arising after clamping force removal, the contact at the interfaces between cover plates and flanges induced by welding, and the application of post-strengthening loads up to the point of elastic LTB initiation for the strengthened system, as determined by eigenvalue analysis. A simplified design equation is then proposed to quantify the post-strengthening critical moment capacity. The validity of the equation is assessed against FE results and its merits and limitations are discussed. The study shows that web distortional effects play a crucial role in reducing the elastic critical moment capacity. Practical recommendations are provided to mitigate such distortional effects and hence maximize the elastic critical moment capacity of the strengthened beams. The second contribution formulates a variational principle for the LTB analysis of doubly symmetric beams strengthened symmetrically with identical steel cover plates. The formulation considers the full sequence of loading and strengthening and captures the effects of pre-strengthening loads and the beneficial effects of pre-buckling deformation (PBD). The study examines the effect of geometry, partial strengthening schemes, presence of different pre- and post-strengthening load patterns, and load height effects. The variational principle is subsequently used to develop a FE formulation, culminating in a quadratic eigenvalue problem. The validity of the FE formulation is assessed through comparisons with other numerical techniques predictions as well as experimental results by others, and subsequently used to conduct a parametric study to characterize the gain in elastic critical moment capacity attained by cover plate strengthening. For beams partly strengthened with cover plates along their spans, the study identifies the optimum locations for cover plates that maximize the critical moments. The third contribution builds upon the variational principle developed by formulating a simple and approximate energy-based design-oriented solution to quantify the LTB resistance of simply supported I-beams strengthened with cover plates. The solution captures the detrimental effect of loads acting on the beam before strengthening and the beneficial effects resulting from PBD, pre- and post-strengthening load heights, as well as moment gradient effects. The potential use of the equations developed in practical applications involving beam strengthening is illustrated through design examples. The fourth contribution expands the variational formulation to include beams with monosymmetric cross-sections and/or symmetric beams with unsymmetric cover plate geometries. The modified variational principle is used to develop a thin-walled beam FE formulation, which is subsequently employed to predict the non-distortional LTB capacity of monosymmetric strengthened beams. Comparative analyses with shell models confirm the validity of the proposed solutions, and practical design recommendations for suppressing web distortion are provided. The effects of various design parameters on the total elastic critical moment capacity are evaluated in a systematic parametric study. The study identifies the loading conditions under which the magnitude of pre-strengthening loads significantly influences the predicted total critical moments. The solutions developed in the present study equip structural designers and analysts with novel techniques that reliably quantify the LTB strength of steel beams strengthened with cover plates, thus enabling them to optimize strengthening strategies for beams whose strengths are governed by LTB modes of failure.

Der in den Ingenieurwissenschaften zunehmend populäre Einsatz der Origami-Technik eröffnet neue Möglichkeiten zur Herstellung von effizienten Tragkonstruktionen [1]–[5]. In Verbindung mit leistungsfähigen, zementbasierten Verbundwerkstoffen bietet die Origami-Technik einen innovativen Ansatz für Entwurf und Realisierung von leichten tragenden Strukturen nach dem Prinzip form follows force – dem Grundgedanken des SPP 1542. [Aus: Motivation und Zielsetzung] / The increasingly popular use of origami technology in the engineering sciences opens up new possibilities for the manufacture of efficient load-bearing structures [1]–[5]. In combination with high-performance, cement-based composite materials, origami technology of ers an innovative approach to the design and realisation of lightweight load-bearing structures based on the principle form follows force –the basic idea of SPP 1542. [Off: Motivation and objectives]

aus dem Inhalt: „Die im Teilprojekt Sobek (siehe S. 626 ff .) entwickelte gefrorene Sandschalung zur abfallfreien Herstellung von Betonbauteilen wurde im Rahmen des BMBF-geförderten Konsortiums Carbon Concrete Composite – C3 für die Herstellung dünnwandiger und gekrümmter Sandwichelemente weiterentwickelt. Der vorliegende Kurzbericht fasst die Forschungsergebnisse des Projekts C3Sandwich zusammen. Eine ausführliche Beschreibung der Arbeiten wurde in [1] veröffentlicht....” / from teh content: „Within the framework of the BMBF-funded consortium Carbon Concrete Composite – C3, the research on sand formwork for the waste-free production of concrete components (TP Sobek, p. 626 seq.) was further advanced towards the production of thin-walled and curved sandwich elements. This report summarizes the research results of the project C3Sandwich. A detailed description of the work was published in [1]....”

The considerable progress in the research and development of thin-walled beam structures responds to their growing use in engineering construction and to their increased need for efficiency in strength and cost. The result is a structure that exhibits large shear strains and important non uniform warping under different loadings, such as non uniform torsion, shear bending and distortion.<p><p>A unified approach is formulated in this thesis for 3D thin walled beam structures with arbitrary profile geometries, loading cases and boundary conditions. A single warping function, defined by a linear combination of longitudinal displacements at cross sectional nodes (derived from Prokic work), is enhanced and adapted in order to qualitatively and quantitatively reflect and capture the nature of a widest possible range of behaviors. Constraints are prescribed at the kinematics level in order to enable the study of arbitrary cross sections for general loading. This approach, differing from most published theories, has the advantage of enabling the study of arbitrary cross sections (closed/opened or mixed) without any restrictions or distinctions related to the geometry of the profile. It generates automatic data and characteristic computations from a kinematical discretization prescribed by the profile geometry. The amount of shear bending, torsional and distortional warping and the magnitude of the shear correction factor is computed for arbitrary profile geometries with this single formulation.<p><p>The proposed formulation is compared to existing theories with respect to the main assumptions and restrictions. The variation of the location of the torsional center, distortional centers and distortional rotational ratio of a profile is discussed in terms of their dependency on the loading cases and on the boundary conditions.<p><p>A 3D beam finite element model is developed and validated with several numerical applications. The displacements, rotations, amount of warping, normal and shear stresses are compared with reference solutions for general loading cases involving stretching, bending, torsion and/or distortion. Some examples concern the case of beam assemblies with different shaped profiles where the connection type determines the nature of the warping transmission. Other analyses –for which the straightness assumption of Timoshenko theory is relaxed– investigate shear deformation effects on the deflection of short and thin beams by varying the aspect ratio of the beam. Further applications identify the cross sectional distortion and highlight the importance of the distortion on the stresses when compared to bending and torsion even in simple loading cases. <p><p>Finally, a non linear finite element based on the updated lagrangian formulation is developed by including torsional warping degrees of freedom. An incremental iterative method using the arc length and the Newton-Raphson methods is used to solve the non linear problem. Examples are given to study the flexural, torsional, flexural torsional and lateral torsional buckling problems for which a coupling between the variables describing the flexural and the torsional degrees of freedom occurs. The finite element results are compared to analytical solutions based on different warping functions and commonly used in linear stability for elastic structures having insufficient lateral or torsional stiffnesses that cause an out of plane buckling. <p> / Doctorat en sciences appliquées / info:eu-repo/semantics/nonPublished

Indiana University-Purdue University Indianapolis (IUPUI) / Crashworthiness design is gaining more importance in the automotive industry due to high competition and tight safety norms. Further there is a need for light weight structures in the automotive design. Structural optimization in last two decades have been widely explored to improve existing designs or conceive new designs with better crashworthiness and reduced mass. Although many gradient based and heuristic methods for topology and topometry based crashworthiness design are available these days, most of them result in stiff structures that are suitable only for a set of vehicle components in which maximizing the energy absorption or minimizing the intrusion is the main concern. However, there are some other components in a vehicle structure that should have characteristics of both stiffness and flexibility. Moreover, the load paths within the structure and potential buckle modes also play an important role in efficient functioning of such components. For example, the front bumper, side frame rails, steering column, and occupant protection devices like the knee bolster should all exhibit controlled deformation and collapse behavior. This investigation introduces a methodology to design dynamically crushed thin-walled tubular structures for crashworthiness applications. Due to their low cost, high energy absorption efficiency, and capacity to withstand long strokes, thin-walled tubular structures are extensively used in the automotive industry. Tubular structures subjected to impact loading may undergo three modes of deformation: progressive crushing/buckling, dynamic plastic buckling, and global bending or Euler-type buckling. Of these, progressive buckling is the most desirable mode of collapse because it leads to a desirable deformation characteristic, low peak reaction force, and higher energy absorption efficiency. Progressive buckling is generally observed under pure axial loading; however, during an actual crash event, tubular structures are often subjected to oblique impact loads in which Euler-type buckling is the dominating mode of deformation. This undesired behavior severely reduces the energy absorption capability of the tubular structure. The design methodology presented in this paper relies on the ability of a compliant mechanism to transfer displacement and/or force from an input to desired output port locations. The suitable output port locations are utilized to enforce desired buckle zones, mitigating the natural Euler-type buckling effect. The problem addressed in this investigation is to find the thickness distribution of a thin-walled structure and the output port locations that maximizes the energy absorption while maintaining the peak reaction force at a prescribed limit. The underlying design for thickness distribution follows a uniform mutual potential energy density under a dynamic impact event. Nonlinear explicit finite element code LS-DYNA is used to simulate tubular structures under crash loading. Biologically inspired hybrid cellular automaton (HCA) method is used to drive the design process. Results are demonstrated on long straight and S-rail tubes subject to oblique loading, achieving progressive crushing in most cases.

The objective of this research is to develop a method to evaluate important weld dimensions in thin plates by using laser generated ultrasounds and EMAT receiver. The superimposed laser sources (SLS) technique is developed to generate narrowband Lamb waves with fixed wavelengths in thin plates. The method permits the flexibility of selecting desired wavelength. The signal processing procedure that combines wavenumber-frequency (k-w) domain filtering and synthetic phase tuning (SPT) is used to further reduce the complexity of Lamb waves. The k-w domain filtering technique helps to filter out the unwanted wave components traveling at the direction that is not of interest to us and the SPT technique is applied to amplify and isolate a particular Lamb wave mode. The signal processing procedure facilitates the calculation of reflection coefficients of Lamb waves that result from the presence of weld joints. The SLS and signal processing procedure are then applied to measure reflection coefficients in butt welds and lap welds. Two methods, the direct method and indirect method, are used to develop models that use reflection coefficients as predictors to predict these weld dimensions. The models developed in this research are shown to accurately predict weld dimensions in thin plates.