The medical treatment of children and the Children's Act 38 of 2005

During the last decade a considerable number of statutes were adapted in South Africa pertaining to the medical treatment of children. Following international norms regarding this matter, South African law also prescribes a minimum age of consent for children seeking medical treatment without the parent’s or guardian’s consent. The long awaited Children’s Act revolutionised child law in South Africa in that it is a piece of legislation touching on a wide spectrum of issues which impact on children’s lives. Before the Children’s Act, matters regarding children were found in scattered fragments in a number of Acts and were not always focused on the child. The Act was hailed by children’s rights activists and generally welcomed. However, as with all legislation, the Act is not without its shortcoming and there are several areas which are vulnerable to criticism. In any communication or transfer of information, the manner in which the message or information is constructed will influence the ultimate decision. The Act does not address the manner or mode in which information is conveyed to the child. For instance, it does not address the predisposition that the medical practitioner consulting the child may have, nor does it require an impartial medical practitioner to assist the child in his/her assessment and decision in the matter. In this regard, the caution offered by Du Preez may be applicable, that “if the effective meaning of the information predominates over the conceptual meaning thereof, the listener/ reader will fail to make a proper judgement of what is being said.” 1 Section 129 does not contain any guidelines or provisions on how a medical practitioner should test whether a child has the mental capacity to understand the information regarding the proposed treatment. The study will report on the results of a consultation with a counselling and educational psychologist to determine which tests or methods could be used by medical practitioners to evaluate the maturity of child patients and the implications this could have on the child and his/her medical treatment. The prerequisites as set out in the new Children’s Act will be examined and the possible problems which might occur will be discussed. CopyrightDissertation (LLM)--University of Pretoria, 2012.Private Lawunrestricte

Towards Qualification of Additively Manufactured Ti6Al4V (ELI) Medical Implants

Published ArticleIn recent years, the production of customized medical implants through additive manufacturing by the Centre for Rapid Prototyping and Manufacturing in South Africa has grown significantly. While satisfactory results have been obtained and the quality of life of many patients has been improved, further research is required to enable the production of qualified components. This paper shares the growing acceptance of additive manufacturing, as well as the establishment of a South African Additive Manufacturing Strategy. An overview of the progress made by the Collaborative Programme in Additive Manufacturing is presented. The scope of the metals research performed towards the qualification of additive manufacturing of Ti6Al4V medical implants is discussed. Examples are given of internationally leading work on utilizing these implants, which were additively manufactured under an ISO 13485 system, in maxillofacial reconstructive surgery. Lastly, the development of an affordable polyurethane artificial heart valve is presented as a different type of medical implant

Crystallographic Texture Analysis of As-Built and Heat-Treated Ti6Al4V (ELI) Produced by Direct Metal Laser Sintering

ArticleThis paper reports on an investigation of crystallographic texture of as-built and heat-treated Ti6Al4V (ELI) produced by direct metal laser sintering (DMLS). The texture analyses were conducted using electron backscatter di raction (EBSD). The -phase texture from the obtained EBSD data was ascertained based on a reconstruction method using the Automatic Reconstruction of Parent Grain for EBSD data (ARPGE) program. A significant improvement of the maximum intensity of the texture from the pole figure was also noted upon heat treatment. The as-built samples and samples heat-treated just below the ! transformation temperature showed a stronger fibrous texture of the reconstructed -grains with the h100i directions almost parallel to the build direction. The alignment of the fibrous texture in the build direction disappeared after heat treatment above the ! -grain transformation temperature

Effect of Stress-Relieving Heat Treatment on the High Strain Rate Dynamic Compressive Properties of Additively Manufactured Ti6Al4V (ELI)

ArticleA study was undertaken on the compressive high strain rate properties and deformation behaviour of Direct Metal Laser-Sintered (DMLS) Ti6Al4V (ELI) parts in two separate forms: as-built (AB) and stress relieved (SR). The high strain rate compression tests were carried out using a Split Hopkinson Pressure Bar test system at ambient temperature. The average plastic strain rates attained by the system were 400 s1 and 700 s1. Comparative analyses of the performance (flow stresses and fracture strains) of AB and SR specimens were carried out based on the results obtained at these two plastic strain rates. Microstructural analyses were performed to study the failure mechanisms of the deformed specimens and fracture surfaces. Vickers microhardness test values were obtained before and after high strain rate compression testing. The results obtained in both cases showed the strain rate sensitivity of the stress-relieved samples to be higher in comparison to those of as-built ones, at the same value of true strain

Effects of Stress-Relieving Heat Treatment on Impact Toughness of Direct Metal Laser Sintering (DMLS)-Produced Ti6Al4V (ELI) Parts

Published ArticleThe impact toughness of as-built (AB) and stressed-relieved (SR) direct metal laser sintering-produced Ti6Al4V (ELI) was investigated using the standard Charpy impact test over the temperature range of 130 C to 250 C. Stressrelieving heat treatment was conducted at 650 C for a soaking period of 3 h in argon gas atmosphere. The results showed improvements in the impact toughness after stress-relieving heat treatment. Stress relieving also shifted the established ductile-to-brittle transition temperature to lower temperatures. Comparative analysis of the impact toughness values for AB and SR specimens at ambient temperature showed them to be 48% and 22% lower than recommended values for use in aircraft structures, respectively

Numerical Simulation of the Taylor Impact Test for Laser Powder Bed Fusion Parts Based on Microstructural Internal State Variables

The response of any engineering design components to stresses should be predictable, While the response of a material to complex loading, such as high strain rates experienced during service, is difficult to represent with simple tests, the Taylor impact test is one of a number of tests devised for high strain rate complex loading. To expedite the acceptance of LPBF Ti6Al4V (ELI) for use in demanding structural applications, there is a need to develop numerical models based on the internal microstructural state variables to predict the performance of the alloy over a wide range of high strain rates using such complex tests. This paper documents the numerical simulation of Taylor impact tests for direct metal laser-sintered and post-processed Ti6Al4V (ELI—Extra Low Interstitial) alloy. A microstructural variable-based constitutive model was used to predict the mechanical properties (stresses and evolution of plastic strains) of the material. The corresponding material parameters of the model were based on the specific microstructure obtained upon post-process heat treatment. The model was first implemented as a user material subroutine in the explicit finite element program ABAQUS using the VUHARD subroutine. Subsequently, the symmetrical Taylor impact tests of Laser Powder Bed Fusion (LPBF) Ti6Al4V (ELI) parts were numerically simulated using the VUHARD subroutine at different impact velocities. The equivalent von Mises stress and plastic strain obtained from numerical simulations were compared with the analytical solutions based on the strain rates obtained. It was shown that the instantaneous and average absolute errors between the numerical and analytical values of the model were generally less than 5%. The mushroom end, commonly observed in a Taylor test specimen, was also seen in the numerical model

Plasma Spheroidisation of Irregular Ti6Al4V Powder for Powder Bed Fusion

Metal powders suitable for use in powder bed additive manufacturing processes should ideally be spherical, dense, chemically pure and of a specified particle size distribution. Ti6Al4V is commonly used in the aerospace, medical and automotive industries due to its high strength-to-weight ratio and excellent corrosion resistance properties. Interstitial impurities in titanium alloys have an impact upon mechanical properties, particularly oxygen, nitrogen, hydrogen and carbon. The plasma spheroidisation process can be used to spheroidise metal powder consisting of irregularly shaped particles. In this study, the plasma spheroidisation of metal powder was performed on Ti6Al4V powder consisting of irregularly shaped particles. The properties of the powder relevant for powder bed fusion that were determined included the particle size distribution, morphology, particle porosity and chemical composition. Conclusions were drawn regarding the viability of using this process to produce powder suitable for additive manufacturing

Fused tracks and layers of Ti10Mo6Cu data obtained via laser powder bed fusion

Laser powder bed fusion (LPBF) has opened the window of in-situ alloying elemental powders for specific engineering and biomedical applications. However, since the LPBF process is non-linear, and the current numerical models are still at the experimental stage it is obligatory to determine the optimum process parameters for each powder composition. The current experimental data described the effects of laser powers and scanning speeds on fused tracks and layers produced using Ti10Mo6Cu powder blend. Fused single tracks were produced at varying scanning speeds and laser powers. The process parameter that falls within the conduction mode threshold was used to produce double layers at varied hatch distances. Layers were rescanned at an offset distance of half the hatch distances. The fused tracks and layers were metallurgically prepared according to the Struers protocol and etched with Kroll's reagent. Optical and scanning electron microscopes were used to measure the width (W), depth of penetration (D), and height (H) of the fused tracks to obtain the data for characterizing the geometry of the fused tracks. Data on the surface quality of the fused layers were extracted with a Surftest SJ-210 portable surface roughness tester, while microhardness test data was extracted using a FM-700 Digital Vickers Microhardness Tester. The data obtained could be used for validating numerical and analytical models, and for predicting fused track profiles. Data that originated from the layers could be used to predict the morphology of layers and the dispersion of elements during in-situ alloying. The methodology applied could be used by other researchers to determine the process parameters for other powder blend compositions and increase the materials database for the LPBF process

Quasi-Static Mechanical Properties of Post-Processed Laser Powder Bed Fusion Ti6Al4V(ELI) Parts under Compressive Loading

The Ti6Al4V structures in aircraft and biomedical industries are usually exposed to quasi-static loads. Therefore, understanding the quasi-static behaviour of this alloy manufactured by an additive manufacturing process is paramount. This paper documents an investigation of the quasi-static mechanical properties of various microstructures of heat-treated Ti6Al4V(ELI) parts manufactured by laser powder bed fusion (LPBF). The effects of different quasi-static strain rates on different microstructures of these samples and their strain hardening are also presented. The test samples were produced using an EOSINT M280 direct metal laser sintering (DMLS) machine and, thereafter, subdivided into three major groups, namely samples C, D and E, for high-temperature annealing at different heat treatment strategies. A universal hydraulic testing machine (UTM) was used to carry out tests at strain rates of 0.001 s−1, 0.005 s−1 and 0.1 s−1. The three forms of LPBF Ti6Al4V(ELI) were found to be sensitive to quasi-static strain rate, whereby values of yield and flow stresses in each form of alloy increased with increasing strain rate. The order of the strength at each strain rate from the highest to the lowest was found to be samples C, D and E. The effects of strain rate on flow hardening were found to be significant in samples C and insignificant in samples D and E

Additive Manufacturing of Ti-Based Intermetallic Alloys: A Review and Conceptualization of a Next-Generation Machine

TiAl-based intermetallic alloys have come to the fore as the preferred alloys for high-temperature applications. Conventional methods (casting, forging, sheet forming, extrusion, etc.) have been applied to produce TiAl intermetallic alloys. However, the inherent limitations of conventional methods do not permit the production of the TiAl alloys with intricate geometries. Additive manufacturing technologies such as electron beam melting (EBM) and laser powder bed fusion (LPBF), were used to produce TiAl alloys with complex geometries. EBM technology can produce crack-free TiAl components but lacks geometrical accuracy. LPBF technology has great geometrical precision that could be used to produce TiAl alloys with tailored complex geometries, but cannot produce crack-free TiAl components. To satisfy the current industrial requirement of producing crack-free TiAl alloys with tailored geometries, the paper proposes a new heating model for the LPBF manufacturing process. The model could maintain even temperature between the solidified and subsequent layers, reducing temperature gradients (residual stress), which could eliminate crack formation. The new conceptualized model also opens a window for in situ heat treatment of the built samples to obtain the desired TiAl (γ-phase) and Ti3Al (α2-phase) intermetallic phases for high-temperature operations. In situ heat treatment would also improve the homogeneity of the microstructure of LPBF manufactured samples