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The machining of hardened steels employing polycrystalline cubic boron nitride and ceramic tooling has been comprehensively investigated over the last 20 years; however, the development of newer cemented carbide grades has extended the use of this group of materials to the machining of steels hardened up to 45 HRC (Rockwell C). The current paper is therefore concerned with continuous turning of AISI 4340 steel hardened from 250 to 525 HV using coated carbide tools in order to investigate whether this cutting tool grade is capable of providing a satisfactory performance when machining a steel with increasing levels of hardness. Machining forces, tool life, and wear mechanisms were assessed and the results indicated that the relationship between the hardness of the work material and the machining force is not straightforward. In general, the machining force components increased with the work material hardness, however, the cutting force decreased slightly as the work hardness increased from 250 to 345 HV. Tool wear was lower when machining the 345 HV workpiece compared with cutting the 250 HV steel. Finally, abrasion was the principal wear mechanism observed and catastrophic failure took place when attempting to machine the 525 HV steel.

BackgroundObtaining informed consent for clinical trials is especially challenging when working in rural, resource-limited areas, where there are often high levels of illiteracy and lack of experience with clinical research. Such an area, a remote field site in the northeastern part of the state of Minas Gerais, Brazil, is currently being prepared for clinical trials of experimental hookworm vaccines. This study was conducted to assess whether special educational tools can be developed to increase the knowledge and comprehension of potential clinical trial participants and thereby enable them to make truly informed decisions to participate in such research.Methodology/Principal FindingsAn informational video was produced to explain the work of the research team and the first planned hookworm vaccine trial, using a pedagogical method based on analogies. Seventy-two adults living in a rural community of Minas Gerais were administered a structured questionnaire that assessed their knowledge of hookworm, of research and of the planned hookworm vaccine trial, as well as their attitudes and perceptions about the researchers and participation in future vaccine trials. The questionnaire was administered before being shown the educational video and two months after and the results compared. After viewing the video, significant improvements in knowledge related to hookworm infection and its health impact were observed: using a composite score combining related questions for which correct answers were assigned a value of 1 and incorrect answers a value of 0, participants had a mean score of 0.76 post-video compared to 0.68 pre-video (p = 0.0001). Similar improvements were seen in understanding the purpose of vaccination and the possible adverse effects of an experimental vaccine. Although 100% of participants expressed a positive opinion of the researchers even before viewing the film and over 90% said that they would participate in a hookworm vaccine trial, an increase in the number who expressed fear of being vaccinated with a novel vaccine was seen after viewing the video (51.4% post-video versus 29.2% pre-video). Increases were also seen in the proportion who thought that participation in a vaccine trial would be inconvenient or disrupt their daily activities.Conclusions/SignificanceEven in rural, resource-limited populations, educational tools can be specially designed that significantly improve understanding and therefore the likelihood of obtaining truly informed consent for participation in clinical research. The observed changes in the knowledge and perceptions of the research participants about hookworm infection and the experimental hookworm vaccine demonstrate that the video intervention was successful in increasing understanding and that the subjects acquired knowledge pertinent to the planned research.