About Residual Stress State of Castings: The Case of HPDC Parts and Possible Advantages through Semi-Solid Processes

Nowadays, one of the most crucial focus in the aluminium-foundry sector is the production of high-quality castings. Mainly, High-Pressure Die Casting (HPDC) is broadly adopted, since by this process is possible to realize aluminium castings with thin walls and high specific mechanical properties. On the other hand, this casting process may cause tensile states into the castings, namely residual stresses. Residual stresses may strongly affect the life of the product causing premature failure of the casting. Various methods can assess these tensile states, but the non-destructive X-Ray method is the most commonly adopted. Namely, in this work, the residual stress analysis has been performed through Sinto-Pulstec μ-X360s. Detailed measurements have been done on powertrain components realized in aluminium alloy EN AC 46000 through HPDC processes to understand and prevent dangerous residual stress state into the aluminium castings. Furthermore, a comparison with stresses induced by Rheocasting processes is underway. In fact, it is well known that Semi-Solid metal forming combines the advantages of casting and forging, solving safety and environmental problems and possibly even the residual stress state can be positively affected.

Rice Hull-Derived Carbon for Supercapacitors: Towards Sustainable Silicon-Carbon Supercapacitors

A simple and effective mixing carbonization-activation process was developed to prepare rice hull-derived porous Si–carbon materials. The morphologies and pore structures of the materials were controlled effectively without any loading or additions at various carbonization temperatures. The structures of the samples changed from large pores and thick walls after 800 ∘C carbonization to small pores and thin walls after 1000 ∘C carbonization. An additional alkali activation–carbonization process led to coral reef-like structures surrounded by squama in the sample that underwent 900 ∘C carbonization (Act-RH-900). This optimal material (Act-RH-900) had a large specific surface area (768 m2 g−1), relatively stable specific capacitance (150.8 F g−1), high energy density (31.9 Wh kg−1), and high-power density (309.2 w kg−1) at a current density of 0.5 A g−1 in 1 M KOH electrolyte, as well as a good rate performance and high stability (capacitance retention > 87.88% after 5000 cycles). The results indicated that Act-RH-900 is a promising candidate for capacitive applications. This work overcomes the restrictions imposed by the complex internal structure of biomass, implements a simple reaction environment, and broadens the potential applicability of biomass waste in the field of supercapacitors.

RECURRENCE OF ANEURYSMAL BONE CYST OF THE MANDIBLE: A CASE REPORT

Аneurysmal bone cysts are benign osteolytic lesions with rapid growth, thin walls containing numerous blood-filled cavities. They occur mainly in the pediatric population but are rarely diagnosed in the facial skeleton. Although benign, the condition can be locally aggressive and cause significant weakening of the affected bone structure. This case report presents a 14-year-old boy with Burkitt's tumor (Non-Hodgkin's lymphoma), previously diagnosed with an aneurysmal bone cyst a year ago. He was admitted for treatment at the Clinic of Maxillo-Facial Surgery of the University Hospital "St. George" Plovdiv due to pain and swelling in the left molar area of the mandibula, dating from 2 days. A recurrence of an aneurysmal bone cyst measuring 55/25 mm, which does not require resection of the mandible, was found. After a decision for surgical removal of the formation, under general anesthesia, and preparation of a three-cornered mucoperiosteal flap, the mandibular bone, which is lysed and thinned by the formation, was trepanned. The roots of the affected teeth were resected, and the formation was extirpated. A gauze drain was placed in the formed cavity, and the wound was sutured. Drug therapy included Cefotaxime 2x1.0 - 10 days, starting 3 days before surgery, and Paracetamol 2x1 – 3 days, 2 days before and 1 day after surgery. Prophylactic examinations were scheduled on day 3, 7, 10, 15 after the operation, as well as 3, 6, and 12 months post-op, due to the recurrent nature of the formation.

Density and Desire: Toward's New Zealand's peculiar urban dream

<p>Density and Desire explores changes in the social organisation of New Zealand, the notion and use of the home, the contribution of dwellings in our cities and an alternative vision for the future dwelling. New Zealand is experiencing a period of rapid transformation that is changing the way we live, work and socialise, as well as our sense of cultural identity. Our population is becoming dramatically more diverse, more urban, and of very different age and family profiles, creating demand for a wider range of housing options that can adapt to changing social patterns. For these reasons and more, we face new questions about living in a community, of dwelling diversity, of promoting sociability, and of creating conditions for neighbourliness. The move towards higher density living in New Zealand’s major cities provides an exciting opportunity for architecture. There is an urgent need to build dwellings and this thesis argues that apartments are a necessary part of our future. However, there is a certain stigma attached to apartment dwelling as ‘second best’ — if you can’t afford a house, you’ll settle for an apartment. The romance of the ‘Quarter-Acre Pavlova Paradise’ (Mitchell) is traded in for a plot peppered with horror stories: paper-thin walls, shoebox-sized ‘chicken coop’ confinement, lack of flexibility, onerous body corporate rules… the list could go on, and it does. The research benchmarks itself against the quantity and the quality of the single detached dwelling on a quarter-acre block both as a spatial measure and the representation of home. By asking ‘how many more dwellings can we get on that space’ and ‘what is the notion of home in the future’, it seeks to resolve some of the problems associated with our initial round of higher density. Domestic architecture can be defined as a system of relationships between oppositions — this thesis explores these relationships through three strategies: Hybrid, Separations & Connections, and Looseness. Each of these deals with the spatial and social characteristics of the city and the home and are used as a technique for controlling relationships at a range of scales and intimacies — from urban to interior — and as a tool for connecting or interrupting the public and private, inside and outside, and building and landscape. Density and Desire offers a conceptual framework with a series of strategies that demonstrate the potential of the apartment building to re-define urban living and the peculiar New Zealand urban dream.</p>

Density and Desire: Toward's New Zealand's peculiar urban dream

<p>Density and Desire explores changes in the social organisation of New Zealand, the notion and use of the home, the contribution of dwellings in our cities and an alternative vision for the future dwelling. New Zealand is experiencing a period of rapid transformation that is changing the way we live, work and socialise, as well as our sense of cultural identity. Our population is becoming dramatically more diverse, more urban, and of very different age and family profiles, creating demand for a wider range of housing options that can adapt to changing social patterns. For these reasons and more, we face new questions about living in a community, of dwelling diversity, of promoting sociability, and of creating conditions for neighbourliness. The move towards higher density living in New Zealand’s major cities provides an exciting opportunity for architecture. There is an urgent need to build dwellings and this thesis argues that apartments are a necessary part of our future. However, there is a certain stigma attached to apartment dwelling as ‘second best’ — if you can’t afford a house, you’ll settle for an apartment. The romance of the ‘Quarter-Acre Pavlova Paradise’ (Mitchell) is traded in for a plot peppered with horror stories: paper-thin walls, shoebox-sized ‘chicken coop’ confinement, lack of flexibility, onerous body corporate rules… the list could go on, and it does. The research benchmarks itself against the quantity and the quality of the single detached dwelling on a quarter-acre block both as a spatial measure and the representation of home. By asking ‘how many more dwellings can we get on that space’ and ‘what is the notion of home in the future’, it seeks to resolve some of the problems associated with our initial round of higher density. Domestic architecture can be defined as a system of relationships between oppositions — this thesis explores these relationships through three strategies: Hybrid, Separations & Connections, and Looseness. Each of these deals with the spatial and social characteristics of the city and the home and are used as a technique for controlling relationships at a range of scales and intimacies — from urban to interior — and as a tool for connecting or interrupting the public and private, inside and outside, and building and landscape. Density and Desire offers a conceptual framework with a series of strategies that demonstrate the potential of the apartment building to re-define urban living and the peculiar New Zealand urban dream.</p>

A shear center demonstration model using 3D-printing

Locating the shear, or flexural, center of non-symmetric cross-sectional beams is a key element in the teaching of structural mechanics. That is, establishing the point on the plane of the cross-section where an applied load, generating a bending moment about a principal axis, results in uni-directional deflection, and no twisting. For example, in aerospace structures it is particularly important to assess the propensity of an airfoil section profile to resist bending and torsion under the action of aerodynamic forces. Cross-sections made of thin-walls, whether of open or closed form are of special practical importance and form the basis of the material in this paper. The advent of 3D-printing allows the development of tactile demonstration models based on non-trivial geometry and direct observation.

Transferability of the working envelope approach for parameter selection and optimization in thin wall WAAM

This work aims to propose and assess a methodology for parameterization for WAAM of thin walls based on a previously existing working envelope built for a basic material (parameter transferability). This work also aimed at investigating whether the working envelope approach can be used to optimize the parameterization for a target wall width in terms of arc energy (which governs microstructure and microhardness), surface finish and active deposition time. To reach the main objective, first, a reference working envelope was developed through a series of deposited walls with a plain C-Mn steel wire. Wire feed speed (WFS) and travel speed (TS) were treated as independent variables, while the geometric wall features were considered dependent variables. After validation, three combinations of WFS and TS capable of achieving the same effective wall width were deposited with a 2.25Cr-1Mo steel wire. To evaluate the parameter transferability between the two materials, the geometric features of these walls were measured and compared with the predicted values. The results showed minor deviations between the predicted and measured values. As a result, WAAM parameter selection for another material showed to be feasible after only fewer experiments (shorter time and lower resource consumption) from a working envelope previously developed. The usage of the approach to optimize parameterization was also demonstrated. For this case, lower values of WFS and TS were capable of achieving a better surface finish. However, higher WFS and TS are advantageous in terms of production time. As long as the same wall width is maintained, variations in WFS and TS do not significantly affect microstructure and microhardness.

A computational method for detecting aspect ratio and problematic features in additive manufacturing

In metal additive manufacturing, geometries with high aspect ratio (AR) features are often associated with defects caused by thermal stresses and other related build failures. Ideally, excessively high AR features would be detected and removed in the design phase to avoid unwanted failure during manufacture. However, AR is scale and orientation independent and identifying features across all scales and orientations is exceptionally challenging. Furthermore, not all high AR features are as easy to recognise as thin walls and fine needles. There is therefore a pressing need for further development in the field of problematic features detection for additive manufacturing processes. In this work, a dimensionless ratio (D1/D2) based on two distance metrics that are extracted from triangulated mesh geometries is proposed. Based on this method, geometries with different features (e.g. thin wall, helices and polyhedra) were generated and evaluated to produce metrics that are similar to AR. The prediction results are compared with known theoretical AR values of typical geometries.By combining this metric with mesh segmentation, this method was further extended to analyse the geometry with complex features. The proposed method provides a powerful, general and promising way to automatically detect high AR features and tackle the relevant defect issues prior to manufacture.

Micro-Range Actuation by Pressure-Induced Elastic Deformation of 316L Steel Membranes Produced by Laser Powder Bed Fusion

In this paper, fundamental research is performed on membrane type actuators made out of 316L stainless steel, manufactured with Laser powder bed fusion (LPBF). A total of six membranes with membrane thicknesses ranging from 0.6 mm up to 1.2 mm were scanned using a high precision metrology system to measure the membrane for displacement at different actuating pressures. The membranes were furthermore investigated for roughness, porosity and thickness. This showed that the thinnest membranes skewed in the print direction when actuated. The remaining membranes achieved higher specific displacements than finite element simulations (FES) predicted, due to surface roughness and porosity. Membrane type actuators can be used for precise actuation within the micrometre range. LPBF allows the creation of internal pockets and membranes in a single metal piece. In opposition to the more commonly used polymers for membrane-type actuators, LPBF steel printed parts offer high stiffness and actuation force. However, due to limitations of the LPBF process on thin walls, large deviations from FES occur. In this paper, a CAD and FES compensation strategy is suggested, which makes future, more complex and effective, designs possible.