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Current procedures of buckling load estimation for thin-walled structures may provide very conservative estimates. Their refinement offers the potential to use structure and material properties more efficiently. Due to the large variety of design variables, for example laminate layup in composite structures, a prohibitively large number of tests would be required for experimental assessment, and thus reliable numerical techniques are of particular interest. The purpose of this paper is to analyze different methods of numerical buckling load estimation, formulate simulation procedures suitable for commercial software and give recommendations regarding their application. All investigations have been carried out for cylindrical composite shells; however similar approaches are feasible for other structures as well.

The authors develop a concept to apply artificial load imperfections with the aim to estimate as good as possible lower bounds for the buckling loads of shells for which the actual physical imperfections are not known. Single and triple perturbation load approach, global and local dynamic perturbation approach and path following techniques are applied to the analysis of a cylindrical composite shell with known buckling characteristics. Results of simulations are compared with published experimental data.

A single perturbation load approach is reproduced and modified. Buckling behavior for negative values of the perturbation load is examined and a pattern similar to a positive perturbation load is observed. Simulations with three perturbation forces show a decreased (i. e. more critical) value of the buckling load compared to the single perturbation load approach. Global and local dynamic perturbation approaches exhibit a behavior suitable for lower bound estimation for structures with arbitrary geometries.

Various load imperfection approaches to buckling load estimation are validated and compared. All investigated methods do not require knowledge of the real geometrical imperfections of the structure. Simulations were performed using a commercial finite element code. Investigations of sensitivity with respect to a single perturbation load are extended to the negative range of the perturbation load amplitude. A specific pattern for a global perturbation approach was developed, and based on it a novel simulation procedure is proposed.

When a thick structure is, on the contrary, subjected to moisture absorption, a fairly long time may be needed to reach full saturation. It is, therefore, important to understand and predict the areas of complex composite structures that are more prone to saturation. The material knock-down factors (proportional to the moisture content) may be applied only to these zones, in order to obtain a less pessimistic structural response prediction. The purpose of this paper is to investigate an FE diffusion model that was used to validate the absorption testing results of thick carbon epoxy laminates.

The experimental results were validated by using a diffusion model in Abaqus FE code.

The absorption results of three 15 mm thick carbon epoxy laminates are presented and reproduced via a mass diffusion model. The laminates were conditioned at 70°C and 85 per cent relative humidity in a moisture chamber. Areas more prone to saturation have been predicted by the FE model and the moisture content in the non-saturated areas has been calculated.

The practical implications of the absorption model are discussed on an example of an aero-engine fan blade-like structure.

Validation of thick panels’ absorption data is an important point of novelty of this paper, given the lack of experimental and modelling validation in the open literature.

This study explores how one novice teacher navigated his first-year teaching sixth-grade social studies.

One-sixth grade novice teacher was observed during his unit on the Islamic Empire. The teacher was interviewed before the unit began to understand his approach to combating Islamophobia and interviewed again after the unit so he could reflect on the unit and discuss if he believed he had accomplished his original goal. Classroom artifacts (handouts, slide decks, etc.) were collected.

The findings highlight the various forces that impacted the decisions the teacher made in the classroom. Lack of support from administration and various colleagues left the teacher feeling overwhelmed and unable to accomplish his goals. While the teacher started the unit with a clear purpose for teaching against Islamophobia, he ultimately taught a unit where students memorized discrete pieces of information.

This study adds to previous research on the need for providing administrative support for novice teachers to be able to teach in ambitious ways by highlighting the numerous shortcomings.

Electron-beam welding has been widely used in industry to join different titanium alloys (Ti-6Al-4V) components. During welding production defects, such as porosity, lack of penetration or thinning are often observed. High-cycle fatigue (HCF) tests have been performed on welded specimens to understand the effect of weld defects on fatigue capabilities. The fatigue life of different types of “defective” welds has been compared against a non-welded reference specimen.

The results of the experimental campaign have been correlated with finite elements models.

It is concluded the geometry produced by the weld process, e.g. toe radius and under-bead shape, and the related stress raisers play a relevant role on fatigue capabilities of welds. This conclusion is valid only for a Ti-6Al-4V T-joint weld and only for flaw initiation. Knock down in materials properties has not been considered.

There is a lack of HCF fatigue data for welds of this geometry and material in the open literature. The paper is of relevance for industrial application and practical interest, although a lot more validation tests are required to draw a final conclusion.

The objective of this paper is to investigate numerically the buckling behavior of submersible composite cylinders.

By means of FEM and golden section method, the search of hoop winding layers, longitudinal winding layers and helical winding layers are studied to optimize the buckling pressure. Considering the mid-strengthening cylinder, the size and distribution of stiffeners are studied systematically.

The results show that laying the hoop winding layers in the two outer sidewalls and the longitudinal winding layers in the middle of the shell is helpful to increase the buckling pressure, and the optimal helical winding angle changes with slenderness ratio.

For mid-strengthening cylinder, the effect of helical winding angle of stiffener on buckling pressure becomes weak gradually with the increase of stiffener thickness. With the increasing of the spacing between stiffeners, the buckling pressure increases first and decreases later. What is more, the mid-strengthening cylinder is less sensitive to the initial geometric imperfections than unstiffened shells.

The purpose of this paper is to derive knockdown factor functions in terms of a shell thickness ratio (i.e. the ratio of radius to thickness) for conventional orthogrid and hybrid-grid stiffened cylinders for the lightweight design of space launch vehicles.

The shell knockdown factors of grid-stiffened cylinders under axial compressive loads are derived numerically considering various shell thickness ratios. Two grid systems using stiffeners – conventional orthogrid and hybrid-grid systems – are used for the grid-stiffened cylinders. The hybrid-grid stiffened cylinder uses major and minor stiffeners having two different cross-sectional areas. For modeling grid-stiffened cylinders with various thickness ratios, the effective thickness (t_eff) of the cylinders is kept constant, and the radius of the cylinder is varied. Thickness ratios of 100, 192 and 300 are considered for the orthogrid stiffened cylinder, and 100, 160, 200 and 300 for the hybrid-grid stiffened cylinder. Postbuckling analyses of grid-stiffened cylinders are conducted using a commercial nonlinear finite element analysis code, ABAQUS, to derive the shell knockdown factor. The single perturbation load approach is applied to represent the geometrical initial imperfection of a cylinder. Knockdown factors are derived for both the conventional orthogrid and hybrid-grid stiffened cylinders for different shell thickness ratios. Knockdown factor functions in terms of shell thickness ratio are obtained by curve fitting with the derived shell knockdown factors for the two grid-stiffened cylinders.

For the two grid-stiffened cylinders, the derived shell knockdown factors are all higher than the previous NASA’s shell knockdown factors for various shell thickness ratios, ranging from 100 to 400. Therefore, the shell knockdown factors derived in this study may facilitate in the development of lightweight structures of space launch vehicles from the aspect of buckling design. For different shell thickness ratios of up to 500, the knockdown factor of the hybrid-grid stiffened cylinder is higher than that of the conventional orthogrid stiffened cylinder. Therefore, it is concluded that the hybrid-grid stiffened cylinder is more efficient than the conventional orthogrid-stiffened cylinder from the perspective of buckling design.

The obtained knockdown factor functions may provide the design criteria for lightweight cylindrical structures of space launch vehicles.

Derivation of shell knockdown factors of hybrid-grid stiffened cylinders considering various shell thickness ratios is attempted for the first time in this study.

The purpose of this paper is to present the probabilistic approach to a new robustness-based design strategy for thin-walled composite structures in post-buckling.

Because inherent uncertainties in geometry, material properties, ply orientation and thickness affect the structural performance and robustness, these variations are taken into account.

The methodology is demonstrated for the sake of simplicity with an unstiffened composite plate under compressive loading, and the probabilistic and deterministic results are compared. In this context, the structural energy and uncertainties are employed to investigate the robustness and reliability of thin-walled composite structures in post-buckling.

As practical implication, the methodology can be extended to stiffened shells, widely used in aerospace design with the aim to satisfy weight, strength and robustness requirements. Moreover, a new argument is strengthened to accept the collapse close to ultimate load once robustness is ensured with a required reliability.

This innovative strategy embedded in a probabilistic framework might lead to a different design selection when compared to a deterministic approach, or an approach that only accounts for the ultimate load. Moreover, robustness measures are redefined in the context of a probabilistic design.

This paper aims to present a new robustness-based design strategy for thin-walled composite structures under compressive loading, which combines strength requirements in terms of the limit and ultimate load with robustness requirements evaluated from the structural energy until collapse.

In order to assess the structural energy, the area under the load-shortening curve between several characteristic points such as local buckling, global buckling, onset of degradation and collapse load is calculated. In this context, a geometrically nonlinear finite element analysis is carried out, in which the ply properties are selectively degraded by progressive failure.

The advantage of the proposed methodology is observed by analyzing unstiffened composite plates under compressive loading, wherein the lightest plate that satisfies both strength and robustness requirements can be attained.

As a practical implication, this methodology gives a new argument to accept the collapse load close to the ultimate load once robustness is ensured.

The structural energy is employed to investigate the robustness of thin-walled composite structures in postbuckling, and new energy-based robustness measures are proposed. In the design of composite structures, this innovative strategy might lead to a more robust design when compared to an approach that only accounts for the ultimate load.

This paper aims to uncover the key enablers of an agile supply chain in the manufacturing sector amidst disruptions such as pandemics, trade wars and cross-border challenges. The study aims to assess the applicability of existing literature to manufacturing and identify additional industry-specific enablers contributing to the field of supply chain management.

The research methodology is comprehensively described, detailing the utilization of extent literature and semistructured interviews with mid- and top-level executives in a supply chain. The authors ensure the robustness of the data collection process and results interpretation.

The study identifies six essential dimensions of an agile supply chain: information availability, design robustness, external resource planning, quickness and speed, public policy influencing skills and cash flow management. The study provides valuable insights for industry professionals to develop agile supply chains capable of responding to disruptions in a rapidly changing world.

This study is limited by its focus on the manufacturing sector, and future research may explore the applicability of these findings to other industries. By focusing on these essential dimensions identified in the study, managers can develop strategies to improve the agility and responsiveness of their supply chains. In addition, further research may investigate how these enablers may vary in different regions or contexts.

The COVID-19 pandemic has forced executives to reconsider their sourcing strategies and reduce dependence on suppliers from specific geographies. To ensure business continuity, companies should assess the risk associated with their suppliers and develop a business continuity plan that includes multisourcing their strategic materials. Digital transformation will revolutionize the supply chain industry, allowing for end-to-end visibility, real time insights and seamless integration of business and processes. Companies should also focus on creating a collaborative workforce ecosystem that prioritizes worker health and well-being. Maintaining trust with stakeholders is crucial, and firms must revisit their relationship management strategies. Finally, to maintain business leadership and competitiveness during volatile periods, the product portfolio needs to be diversified and marketing and sales teams must work in tandem with product teams to position new products accordingly.

This work contributes substantially to the literature on supply chain agility (SCA) by adding several new factors. The findings result in a more efficient and cost-effective supply chain during a stable situation and high service levels in a volatile situation. A less complex methodology for understanding SCA provides factors with a more straightforward method for identifying well-springs of related drivers. First, the study contributes to reestablish the factors such as quickness, responsiveness, competency, flexibility, proactiveness, collaboration and partnership, customer focus, velocity and speed, visibility, robustness, cost-effectiveness, alertness accessibility to information and decisiveness as applicable factors for SCA. Second, the study suggests a few more factors, such as liquidity management, Vendors’ economic assessment and economic diversity, that are the study’s unique contributions in extending the enablers of SCA. Finally, public policy influencing skills, local administration connects and maintaining capable vendors are the areas that were never considered essential for SCA. These factors have emerged as a vital operational factor during the lockdown, and academicians may consider these factors in the future to assess their applicability.

This study provides new insights for decision-makers looking to enhance the resilience and agility of their supply chains. The identification of unique enablers specific to the manufacturing industry contributes to the existing body of literature on agile supply chains in the face of disruptions.