Evaluation of Toughness of High Strength Low Alloy (HSLA) Steels as a Function of Carbon Content

The influence of carbon content on the microstructure and toughness of HSLA steel at room temperature was investigated based on experimental work and literature. It was revealed that increasing the carbon content in from 0.06 to 0.14 wt-% is detrimental to toughness, giving higher impact transition temperature. The deterioration of toughness was correlated to undesired changes in the microstructure, which showed an increase in pearlite volume fraction at the expense of ferrite. At high carbon content, cementite of pearlite was found to grow more rapidly to form continuous plates which act as preferred sites for crack nucleation and propagation. In addition, the lamellar spacing of the pearlite increased as a function of carbon content, which in turn gave worse toughness. The presence of high carbon content and carbide forming elements in the chemical composition was more detrimental to toughness due to the formation of thick carbides around the grain boundaries. These carbides act as a path for crack propagation, which makes it easy for cracks to cohere, leading to intergranular fracture. Keywords - HSLA steel, Carbon, Brittleness, Toughness, Impact Transition Temperature (ITT)

Affects of student attendance on performance in undergraduate materials and manufacturing modules

This paper investigates the class attendance of second year, third year and fourth year students and their overall performance at the school of Mechanical and Manufacturing Engineering in Dublin City University (DCU). An investigation was recently conducted into the delivery of different module which was presented to a group of second year, third year and fourth year engineering students at DCU. Attendance in the class was recorded and the continuous assessment results and the final overall performances were investigated with their attendance. Student performance on Strength of materials – part 1 (SM1), Strength of materials part - 2 (SM2), Mechanics of Materials and Machine (MMM) and Advanced Materials and Manufacturing Processes (AMMP) modules are presented in this paper. This paper presents an examination of some of the factors affecting the overall results of these students. Factors evaluated include attendance of the student, as well as individual performance in continuous assessment and examination. Overall attendance at the lecture, the organised seminar series, and practical work were recorded. Results indicate a direct link between attendance and marks awarded. Students with higher attendance achieved better grades

Designing pulse laser surface modification of H13 steel using response surface method

This paper presents a design of experiment (DOE) for laser surface modification process of AISI H13 tool steel in achieving the maximum hardness and minimum surface roughness at a range of modified layer depth. A Rofin DC-015 diffusion-cooled CO2 slab laser was used to process AISI H13 tool steel samples. Samples of 10 mm diameter were sectioned to 100 mm length in order to process a predefined circumferential area. The parameters selected for examination were laser peak power, overlap percentage and pulse repetition frequency (PRF). The response surface method with Box-Behnken design approach in Design Expert 7 software was used to design the H13 laser surface modification process. Metallographic study and image analysis were done to measure the modified layer depth. The modified surface roughness was measured using two-dimensional surface profilometer. The correlation of the three laser processing parameters and the modified surface properties was specified by plotting three-dimensional graph. The hardness properties were tested at 981 mN force. From metallographic study, the laser modified surface depth was between 37 8m and 150 8m. The average surface roughness recorded from the 2D profilometry was at a minimum value of 1.8 8m. The maximum hardness achieved was between 728 and 905 HV0.1.These findings are significant to modern development of hard coatings for wear resistant applications

Employer and student perspectives on skills for engineers in the twenty first century and beyond

This research focused on skills identified among final year engineering students. It provided evidence of different levels of skills by students and identifies their greatest learning influences in these areas. The skills were self-assessed by students and covered seven areas designated by Engineers Ireland. Competency levels such as science, software, creativity, engineering practice, social and business, ethics, discipline specific were assessed. It also investigated the important role that work placements play in skills developed by students. Key skills sought by leading Engineering firms from graduates now and in the next five years were also researched in this paper. Employers were surveyed to determine and investigate skills needed from graduate engineers and how best to meet these challenges. The emphasis on work placements and its impact on skills’ development in engineering students such as business acumen and working effectively and efficiently in industry were highlighted

Analysis of international graduate programmes structures for engineering education

This article traces the evolution of graduate study in Engineering in Ireland over three decades. Very few studies have shown the different norms and structures of graduate programmes in Ireland. In this paper, a review of traditional and structured PhD in terms of credit requirements and co-ordination structures is presented. The authors summarise the characteristics of graduate programmes in different universities in Ireland and compare these to those obtained in some of the leading international universities. The implementation of graduate programmes in Ireland is relatively recent and the structure of these programmes is still under development in the different universities. Plans for enhancement of graduate programs and the development of new initiatives to support graduate student academic and professional development are very important for the success of these programmes. The growth in enrolment reflects a broad diversity in background of students which will require not only increased financial resources but an adequate and sound organisational structure in order to move forward

The influence of Widmanstätten ferrite, martensite and grain boundary carbides on the strength and impact behaviour of high Al (0.2%) and Nb containing hot rolled steels

The influence of Al and Nb on the strength and impact behaviour of hot rolled 0.06%C, 1.4%Mn steels has been determined after hot rolling to 15 and 30 mm thick plate. When 0.16%Al was added to the plain C-Mn steel, the impact behaviour significantly improved even though Widmanstätten ferrite (WF) was present. This improvement was due to refinement of the grain boundary carbides and removing the N from solution as AlN. The hot rolled steels all contained WF but when Nb was added more WF formed as well as MA giving poor impact behaviour. Reducing the hardenability from that shown in previous work by decreasing C from 0.1 to 0.06%, Nb from 0.03 to 0.02%, and cooling rate from 33 to 17 K/min had no effect in improving the impact performance of hot rolled Nb steels. To ensure optimum properties not only is it necessary to reduce the hardenability, but WF formation must be discouraged by having a high Ar3. This can only be presently achieved by refining the austenite grain size via control rolling the Nb containing steels; the benefit of adding Al can then, readily be seen. Suggestions are made as to how this might be achieved for hot rolling

Laser surface modification of Ti-6Al-4V for biomedical applications

Introduction. Ti-6Al-4V is used in biomedical engineering due to its excellent properties: high strength to weight ratio, low density, high corrosion resistance and good biocompatibility. However, the use of the alloy under severe friction conditions is restricted due to poor tribological properties such as high coefficient of friction and low hardness [1, 2]. Laser surface modification is known for its improved mechanical and tribological properties for biomedical titanium alloys. The treatment produces minimal contamination and increases osseointegration [3-5]. The present study evaluated the effects of high speed, laser processing parameters on surface roughness, hardness, chemical composition and biocompatibility. Materials and Methods A 1.5KW CO2 laser in continuous mode was irradiated on flat Ti-6Al-4V samples at three levels of irradiance 15.72, 20.43 and 26.72 KW/cm2 and three levels of residence time 1.08, 1.44 and 2.16 ms. Evaluation of the surface was carried out by scanning electron microscope (SEM) examination and mechanical profilometry in accordance to ISO 4287/4288. SEM analysis of the surface topography resulting from the various laser treatments was carried out. Energy Dispersive Spectroscopy (EDS) analysis was used to determine the chemical composition of the treated areas. The effect of surface topography on cellular attachment was investigated in vitro using MC3T3-E1 pre-osteoblast cells. Cell attachment was determined using the Hoechst DNA assay and cell morphology was examined using SEM analysis. Results and Discussion An increase in residence time resulted in improved depth of processing. An increase in irradiance did not always produce an increase in depth of processing; however higher irradiance levels were found to provide for a more uniform depth of processing which reached a maximum of 80 µm. Irradiation with the scanning beam produced a single phase microstructure, see Figure 1. This single phase occurred when various constituents in the alloy have dissolved with rapid solidification thwarting segregation of the various alloying elements into high and low concentration [6]. Improved homogenous chemical composition of the laser modified region was verified by the EDS analysis. Microhardness examination revealed an increase in hardness of up to 67% after laser treatment. A relationship between irradiance and roughness was observed, roughness decreasing with increase in irradiance

Effects of Root Exudates on Specific Diazotroph-Rice Genotype Association

Diazotrophs are known to utilize root exudate carbon compounds, form natural associations with rice plants and subsequently fix nitrogen. The specific association can be influenced by the bacterial strains and rice genotypes. A series of experiments were conducted in laboratory and glasshouse conditions with the following objectives; (i) to isolate and characterize the indigenous diazotrophs, (ii) to determine the root exudate sugars and amino acids of different rice genotypes (iii) to determine the utilization of root exudates sugars by the diazotrophs (Rhizobium sp. and Corynebacterium sp.) during colonization and (iv) to determine the effects of specific sugars on plant-diazotrophs associations, biological nitrogen fixation and growth of different rice genotypes. The diazotrophs were isolated from Tanjong Karang rice irrigation project area using N-free semi-solid media and the nitrogenase enzyme activity was determined by Acetylene Reduction Assay (ARA) technique. The isolated diazotrophs were identified using Biolog Identification method. Root exudates sugars and amino acids of the three rice genotypes (Mahsuri, Mayang Segumpal and MR219) were determined using high performance liquid chromatography (HPLC). The root (rhizosphere and endophytic) colonization were visually observed by using Scanning Electron Microscope (SEM) and Transmission Electron Microscope (TEM). The diazotroph–plant association and biological nitrogen fixation (BNF) was estimated using 15N dilution technique in glasshouse condition. Results showed that the indigenous diazotrophic populations were significantly (P<0.01) influenced by soil types, plant age and rice varieties. Bacterial populations were significantly higher in soil (1.8-2.2 x 106 cfu g-1soil) and rhizosphere (1.4-4.2 x 107 cfu g-1 root) of rice grown in Organic Clay & Muck, Bakau, Sedu and Serong soil series. Molecular analysis indicated a diverse group of diazotrophic strains were present in the different soil types. Ten of the strains were identified by the Biolog Identification method as Rhizobium, Burkholderia and Corynebacterium spp.. Biochemical tests of 19 isolates showed that these strains were positive for N2 fixation, capable of degrading cellulose and able to produc high amounts of indoleacetic acid (IAA) which ranged from 15 to 69 mg L-1. The diazotrophs exhibited differences in the specific growth rate, generation time, and utilized mono and disaccharide sugars as sole energy sources. A total of seven sugars and 16 amino acids were determined from rice root exudates. The concentration of root exudate sugars, amino acids and their release patterns differed significantly among rice genotypes. Mahsuri released the highest root exudate sugars (25.73%) followed by MR219 (23.14%) and Mayang Segumpal (20.85%). Inoculated plants produced different amounts of sugars and amino acids compared to non-inoculated plants. Mahsuri inoculated with Corynebacterium sp. (Sb26) released the highest amount of fructose and arabinose, while Mayang Segumpal inoculated with Rhizobium sp. (Sb16) produced the highest amount of sucrose in the root exudate. All rice genotypes produced significantly higher amounts of glycine and isoleucine in root exudates as compared to other amino acids. In general, plants inoculated with Sb16 produced higher amounts of total sugars and amino acids in their root exudates compared to those inoculated with Sb26. A significant relationship was observed between diazotrophic populations and utilization of root exudates sugars and amino acids in the rice genotypes. The Sb16 strain utilized higher amounts of sugars and stimulating higher rhizosphere population compared to Sb26 strain. The diazotrophs were able to colonize and proliferate endophytically in the rice roots. SEM micrographs showed the occurrence of bacterial colonization on surfaces of primary and lateral roots, root hair zone, lateral root junction, in crevices and root tips. TEM view of roots revealed the presence of diazotroph in the intercellular spaces of cortical parenchyma, within epidermis, inner cortex, and near vascular tissue. The results of invitro and glasshouse study using 15N dilution studies showed that Mayang Segumpal inoculated with Sb16 and applied with galactose significantly increased plant-N content and fixed 42 % of atmospheric N (Ndfa). This association increased 147-245 % plant biomass compared to non-inoculated control and 8-52 % over 60 kg ha-1 N-fertilizer application.The study proved that diazotroph inoculation enhanced root exudate sugar production and provides specific sugars for specific diazotroph-rice plant association. Application of galactose and arabinose as external carbon source enhanced the growth and N2 fixation activity of the Rhizobium sp. (Sb16) and Corynebacterium sp. (Sb26), respectively. The association of Mayang Segumpal with Sb16 and MR219 rice with Sb26 significantly improved nitrogen fixation and subsequently plant growth

Investigation of factors affecting the learning of final year advanced materials and manufacturing students

An investigation was recently conducted into the delivery of an Advanced Materials and Manufacturing Processes module which was presented to a sub-group of the final year engineering students at Dublin City University (DCU). Results from the class which has just completed their final year studies were examined in relation to the method of delivery. This cohort consisted of 25 students, 13 which studied for the Computer Aided Mechanical and Manufacturing Engineering (CAM) degree and 12 which studied for the Business and Manufacturing Engineering (BME) degree. This paper presents an examination of some of the factors affecting the overall results of these students. Factors evaluated include attendance of the student, as well as individual performance in continuous assessment and examination. Overall attendance at the lecture, the organised seminar series, and practical work were recorded. Results indicate a direct link between attendance and marks awarded. Students with higher attendance achieved better grades. Good continuous assessment performance did not automatically indicate good exam performance. Contrary evidence to this is discussed in relation to student learning styles where students may show better ability in exams with poorer ability in continuous assessment and vice versa