Search results

The purpose of this paper is to present, the global behaviour of sandwich structures comprising cellular cores is predicted by finite element (FE) analysis. Two modelling approaches are investigated, providing different levels of accuracy; in both approaches, the sandwich structure is idealised as a layered stack with the skin modelled using shell elements; while the core is either modelled with fine detail using beam micro-elements representing the cell struts, or is modelled by three-dimensional solid elements after an appropriate core homogenisation.

The applied homogenisation methodology, as well as the all important modelling issues are presented in detail. Experimental tests performed using a mass-drop testing machine are used for the successful validation of the simulation models.

It was concluded that the core microscale models having detailed FE modelling of the core unit cells geometry with fine scale beam elements are suitable for the analysis of the core failure modes and the prediction of the basic core stiffness and strength properties. It was demonstrated that the homogenised core model provides significant advantages with respect to computing time and cost, although they require additional calculations in order to define the homogenised stress-strain curves.

Special microscale material tests are required for the determination of appropriate materials parameters of the core models, as steel selective laser melting (SLM) microstrut properties differ from the constitutive steel material ones, due to the core manufacturing SLM technique. Stress interactions were not taken into account in the homogenisation, as the applied core material model supports the introduction of independent stress-strain curves; however, the predicted load deflection results appeared to be very close to those obtained from the detailed core micromodels.

The paper is original. The dynamic behaviour of conventional sandwich structures comprising conventional honeycomb type cores has been extensively studied, using simple mass-spring models, energy based models, as well as FE models. However, the response of sandwich panels with innovative SLM cellular cores has been limited. In the present paper, novel modelling approaches for the simulation of the structural response of sandwich panels having innovative open lattice cellular cores produced by SLM are investigated.

This paper aims to explore the influence of the materials used in moulding blocks of hybrid moulds on the injection moulding setup and the properties of the mouldings.

An instrumented (pressure and temperature) hybrid mould with exchangeable moulding blocks, produced by rapid prototyping and tooling techniques (RPT), was used to produce polypropylene tubular mouldings. The configuration of the mould was varied with combinations of moulding block materials, namely, an epoxy resin composite processed by vacuum casting and steel. The processing conditions were adjusted to obtained steady processing conditions. The mouldings were assessed in terms of the microstructure and the shrinkage.

Due to the properties of the moulding block obtained by RPT being different from tool steel, the injection moulding processing conditions and the plastics parts properties are different when hybrid moulds are used. The cycle time depends on the moulding block properties and must be adjusted to the desired running temperature. The morphology of the mouldings is strongly affected by the thermal properties of the moulding block materials. When different materials are used in the core and the cavity asymmetric structures develop in the part. The shrinkage of the mouldings, when resin cores are used is also affected by the deformation of the core caused by the injection pressure.

This paper makes a contribution to understanding the morphology of semi‐crystalline mouldings obtained using hybrid moulds and enhances the importance of the core deformation on the shrinkage of the mouldings.

In this chapter we investigate the role of family-specific factors in facilitating or constraining business exit in family firms. Family business literature seems to have an implicit bias toward continuity and persistence in the founder's business. This is explained by heavy emotional involvement and development of path-dependent core competences over generations. However, several long-lived family firms were able to successfully exit the founder's business. Exit allowed them to free significant strategic resources, which were later reinvested in exploiting novel entrepreneurial opportunities. Our aim is to investigate the process of exit from the founder's business in family firms, to explain both triggers and obstacles to decommitment and de-escalation. We address this issue through the study of the Italian Falck Group's exit from the steel industry in the 1990s, followed by successful startup of a renewable energy business. By carefully triangulating different data sources and different voices within and outside the controlling family, we develop a framework describing family-specific facilitators and inhibitors of business exit, and subsequent startup of a new business. Three types of family-specific factors emerge as relevant in shaping a family firm's likelihood and speed of exit from a failing business: family-related psychological triggers and obstacles to business exit; family-specific components of the structural de-escalation context; family responses to ensuing de-escalation and exit needs. The emerging framework offers a more nuanced interpretation of decommitment activities in family firms, pointing to the differential role family-specific factors may play as facilitators or inhibitors of business exit. We also suggest how these family-specific results may contribute to a deeper understanding of exit in nonfamily firms. Our results also have practical implications for family business entrepreneurial management. Actively managing the different determinants of exit choices that emerged from our study will set the stage for de-escalation from a failing course of action – a dynamic capability all family firms should learn and practice if they intend to transfer their entrepreneurial orientation to next generations.

The purpose of this paper is to study the electric vehicle (EV) drive efficiency of a traction motor considering regenerative braking according to various motor cores.

A software program was developed to predict the driving performance of an EV. It determines the driving mileage, the required power of the traction motor, and the operation points on a torque-speed map when drive cycles are given. The driving performance is calculated from the battery capacity, vehicle specification, and efficiency map of the traction motor computed using the finite element analysis.

As a result, the motor core is a significant design variable for raising the driving mileage of an EV. It is noted that the change of electrical steels used for the motor core is the lowest priced method of increasing the driving range by 2 km.

The comparative analysis of motor core by replacing 35PN250 to 25PNX1250F results in improvement effects traveling 4.62 and 5.16 km farther in the Simplified Federal Urban Driving Schedule (SFUDS) and Highway Fuel Economy Driving Schedule (HWFET), respectively. It was also verified that regenerative braking system is able to enhance drive efficiency by 29-31.3 km in the SFUDS and 6.5-7.3 km in the HWFET. From comparison of price rise for increasing driving mileage by 2 km, it is noted that the change of electrical steels used for the motor core is the lowest priced method.

Nowadays, circular concrete-filled tubular (CFT) columns are largely used in construction because of structural and architectural advantages such as high load bearing capacity and aesthetic appearance. The behavior of CFT columns at ambient and high temperatures is good; however, there are problems related to their behavior in fire when inserted in a real building structure, as for example, the influence of the restraining to thermal elongation that have to be addressed in order to improve their design. This study aims to present the results of a numerical study on the behavior of CFT columns with restrained thermal elongation in case of fire.

The parameters tested in the numerical simulations included column slenderness, load level, surrounding structure stiffness and steel reinforcement ratio. A sequentially coupled thermal stress analysis was carried out. The numerical model was validated with results from a large series of fire resistance tests carried out at Coimbra University, in Portugal. From these, simple equations to evaluate CFT column critical times were derived.

The results were also compared with the ones obtained from the current EN 1994-1-2:2005 simplified calculation and tabulated data methods. For the analyzed cases, it was verified that, while the simplified calculation method led to safe results on the evaluation of the fire resistance of CFT columns with restrained thermal elongation, the tabulated data method led, in certain cases, to unsafe results. This research showed also lower critical times than those from literature on similar type of columns.

The influence of the stiffness of the surrounding structure on the behavior of CFT columns subjected to fire was not yet clear in the major part of the studies already carried out. So, this paper has the originality to consider this parameter in the numerical simulations of this type of columns.

This paper aims to present an accurate representation of laminated wound cores with a low computational cost using 2D and 3D finite element (FE) method.

The authors developed an anisotropy model in order to model laminated wound cores. The anisotropy model was integrated to the 2D and 3D FE method. A comparison between 2D and 3D FE techniques was carried out. FE techniques were validated by experimental analysis.

In the case of no‐load operation of wound core transformers both 2D and 3D FE techniques yield the same results. Computed and experimental local flux density distribution and no‐load loss agree within 2 per cent to 6 per cent.

The originality of the paper consists in the development of an anisotropy model specifically formulated for laminated wound cores, and in the effective representation of electrical steels using a composite single‐valued function. By using the aforementioned techniques, the FE computational cost is minimised and the 3D FE analysis of wound cores is rendered practical.

The purpose of this study is to develop a topological model of a three-phase, three-limb transformer for low-frequency transients. The processes in the core limbs and yokes are reproduced individually by means of a dynamic hysteresis model (DHM). A method of accounting for the transformer tank with vertical magnetic shunts at the tank walls is proposed and tested on a 120 MVA power transformer.

The model proposed has been implemented independently in a dedicated Fortran program and in the graphical pre-processor ATPDraw to the ATP version of the electromagnetic transient program.

It was found that the loss prediction in a wide range of terminal voltages can only be achieved using a DHM with variable excess field component. The zero sequence properties of the transformer can be accurately reproduced by a duality-derived model with Cauer circuits representing tank wall sections (belts).

In its present form, the model proposed is suitable for low-frequency studies. Its usage in the case when transformer capacitances are involved should be studied additionally.

The presented model can be used either as an independent tool or serve as a reference for subsequent simplifications.

The model proposed is aimed at meeting the needs of electrical engineering and ecology-minded customers.

Till date, there were no experimental data on zero-sequence behavior of three-phase, three-limb transformer with vertical magnetic shunts, so no verified transient model existed. The model proposed is probably the first that matched this behavior and reproduced measured no-load losses for a wide voltage range.

Sandwich construction with aluminium honeycomb cores bonded to faces with the adhesive films Redux 775, 775R and Bloomingdale FM‐47 is discussed. Drawings showing its applications to a series of components for various hypothetical aircraft arc included. Sandwich materials for supersonic aircraft of the types now entering production are reviewed, as well as the application techniques of the new Redux films. Some rules gathered from experience for the design of components with honeycomb cores, and solutions of special design problems with hypothetical wing panels, are treated. The paper then deals fairly fully with results from a programme of FFA investigations on this type of structure. The specimens discussed were bonded with Redux 775 and FM‐47 and consisted partly of tensile tests on cores, compressive tests on sandwich columns and shear tests on various sandwich webs. Design curves have been plotted in some cases. Further results are presented showing the influence of temperature on the shear strength of an aluminium alloy core and Redux 775 and FM‐47 films. Also a few creep results are given where the object of the tests has been to determine the optimum curing temperature and time for applying Redux 775 to yield minimum creep values. The room‐temperature results illustrate the excellent properties of honeycomb structures and the elevated‐temperature results indicate that bonded uninsulated aluminium sandwiches can be retained, even when the temperature due to kinetic heating approaches 70 deg. C. Finally, some remarks regarding future developments are made on various new ‘temperature‐resistant’ adhesives and on combinations of various materials for sandwich panels with external insulation, suitable for certain types of the next breed of supersonic aircraft.

The purpose of this paper is to introduce a method for evaluating the production tolerances influence on the practically realized optimal solution of electrotechnical devices. The influence is estimated by the optimal solution range defined with a given probability.

Because of the tolerances nature, the paper is in probabilistic categories. The accent is put on the cases when the mathematical description of the cost function is analytical, for example polynomial found on the basis of the design of experiments and response surface methodology. The optimal solution range is defined with a given probability. The governing equation is Chebychev's inequality. In some cases, Chebychev's inequality would be rather weak but the advantage is that it is valid for all kinds of probabilistic distributions.

A numerical example – an electrical machine – is considered with respect to variances in the magnetic characteristics of the stator and rotor core electrotechnical steel and tolerances in the geometrical dimensions of the machine. An analytical expression for the variance of the optimal solution is obtained in the case of a second order polynomial cost function. It is found that the energetic characteristic of the realized optimal design is expected to be negligibly different from its value in the proposed optimal project.

Although the example concerns the field of electrical machines, the methodology can be of interest for other domains and for different electrotechnical devices.

The purpose of this review paper is to provide a review of the most recent advances in the field of manufacturing composite sandwich panels along with their advantages and limitations. The other purpose of this paper is to familiarize the researchers with the available developments in manufacturing sandwich structures.

The most recent research articles in the field of manufacturing various composite sandwich structures were reviewed. The review process started by categorizing the available sandwich manufacturing techniques into nine main categories according to the method of production and the equipment used. The review is followed by outlining some automatic production concepts toward composite sandwich automated manufacturing. A brief summary of the sandwich manufacturing techniques is given at the end of this article, with recommendations for future work.

It has been found that several composite sandwich manufacturing techniques were proposed in the literature. The diversity of the manufacturing techniques arises from the variety of the materials as well as the configurations of the final product. Additive manufacturing techniques represent the most recent trend in composite sandwich manufacturing.

This work is valuable for all researchers in the field of composite sandwich structures to keep up with the most recent advancements in this field. Furthermore, this review paper can be considered as a guideline for researchers who are intended to perform further research on composite sandwich structures.