Response of A356 to warm rotary forming and subsequent T6 heat treatment

The through-process microstructural effects in A356 subjected to rotary forming at elevated temperatures have been investigated. Macro and micro-hardness testing have been used extensively to track changes in the material from the as-cast state to as-formed, and T6 heat treated. Targeted thermal treatments have been used to isolate the effects of mechanical deformation through comparative measurements. These measurements include macro and micro hardness measurements, Energy-dispersive X-ray analysis and examination of eutectic-Si particle size and morphology. The results indicate that the as-cast material is stable up to approximately 144{\deg}C, with the rotary formed material exhibiting decreased macrohardness in-line with the time spent at elevated temperature. Post heat treatment, there was a significant decrease in hardness with increased levels of deformation. Results indicate that precipitation hardening is not appreciably affected by rotary forming, and the principal cause for the drop in hardness with deformation is due to the condition of Al-Si eutectic phase.Comment: 26 pages, 13 figure

Analysis and modelling of a rotary forming process for cast aluminum alloy A356

Spinning of a common aluminum automotive casting alloy A356 (Al-7Si-0.3 Mg) at elevated temperatures has been investigated experimentally with a novel industrial-scale apparatus. This has permitted the implementation of a fully coupled thermomechanical finite element model aimed at quantifying the processing history (stress, strain, strain-rate and temperature) and predicting the final geometry. The geometric predictions of this model have been compared directly to the geometry of the workpieces obtained experimentally. This study is novel in regards to both the size and shape of the component as well as the constitutive material representation employed. The model predictions are in reasonable agreement with experimental results for small deformations, but errors increase for large deformation conditions. The model has also enabled the characterization of the mechanical state which leads to a common spinning defect. Suggestions for improving the accuracy and robustness of the model to provide a predictive tool for industry are discussed

Auditory hallucinations in youth:occurrence, clinical significance and intervention strategies

The thesis ‘Auditory Hallucinations in Youth’ is about auditory hallucinations in children and adolescents (hereafter ‘youth’). Experiencing an auditory hallucination means that someone hears something in the absence of an identifiable stimulus (‘sound’). Auditory hallucinations can differ from undefinable sounds or mumbling to hearing clear music and/or hearing voices whispering or shouting. In the case of ‘hearing voices’, this is also called auditory verbal hallucinations. Previous research points to the frequent occurrence of auditory hallucinations. However, prevalence rates varied widely. Auditory hallucinations in youth are often transient. Nevertheless, while present, they can cause severe suffering and even be a symptom of psychopathology. Research following this thesis shows that almost one in ten people ever experience an auditory hallucination, with higher rates in children (12.7%) and adolescents (12.4%) than in adults (5.8%) and the elderly (4.5%). About a quarter (23.6%) of young adolescents hearing voices is in need of clinical care. Youth seeking help for hearing voices suffer highly consequent to the impact of their voices, but also to the presence of various and often multiple psychiatric diagnoses. Therefore, youth hearing voices warrant a broad clinical assessment. Treatment should always first aim at possible underlying causes and psychoeducation regarding auditory hallucinations. The newly developed psychotherapy Stronger Than your Voices is effective to increase coping regarding hearing voices and subsequently reduce the impact of the voices

Constitutive behavior of as-cast A356

The constitutive behavior of aluminum alloy A356 in the as-cast condition has been characterized using compression tests performed over a wide range of deformation temperatures (30-500{\deg}C) and strain rates (\approx0.1-10 /s). This work is intended to support the development of process models for a wide range of conditions including those relevant to casting, forging and machining. The flow stress behavior as a function of temperature and strain rate has been fit to a modified Johnson-Cook and extended Ludwik-Hollomon expression. The data has also been assessed with both the strain-independent Kocks-Mecking and Zener-Hollomon frameworks. The predicted plastic flow stress for each expression are compared. The results indicate that the extended Ludwik-Hollomon is best suited to describe small strain conditions (stage III hardening), while the Kocks-Mecking is best employed for large strain (stage IV). At elevated temperatures, it was found that the Zener-Hollomon model provides the best prediction of flow stress.Comment: 34 pages, 12 figure

Analytical solution of the tooling/workpiece contact interface shape during a flow forming operation

Flow forming involves complicated tooling/workpiece interactions. Purely analytical models of the tool contact area are difficult to formulate, resulting in numerical approaches that are case-specific. Provided are the details of an analytical model that describes the steady-state tooling/workpiece contact area allowing for easy modification of the dominant geometric variables. The assumptions made in formulating this analytical model are validated with experimental results attained from physical modelling. The analysis procedure can be extended to other rotary forming operations such as metal spinning, shear forming, thread rolling and crankshaft fillet rolling.Comment: 28 pages, 11 figure