Multiwire submerged arc welding of steel structures

The assembly of large structures made out of thick steel plates requires a welding process by which multiple wires can be used simultaneously. To reproduce these industrial processes in a research environment, OCAS has invested in a multiwire submerged arc welding (SAW) setup. In this multiwire setup, up to five wires in tandem configuration can be used. The objective of this master thesis is to establish a deeper knowledge of process parameters used to weld steel plates in a thickness range of 12,7 up to 25 mm, by means of the submerged arc welding process. Based on literature, a test matrix is composed in which the number of wires, the plate thickness and other weld parameters are the variables. In addition, a specific plate preparation for each plate thickness is derived from the literature. The preformed weld trails will be evaluated on weld bead geometry and metallographic properties. There is further experimental examination required, which will result in the revising of the matrix

LME susceptibility of galvanised welded structures of high strength steels

Hot dip galvanizing is a very popular and well known process in corrosion protection of steel. However, very occasionally, cracks appear on structures when they leave the zinc bath. The responsible crack phenomenon appears to be liquid metal embrittlement. This phenomenon is already known for a long time, but it is still not yet fully understood. The lack of fundamental theoretical knowledge and the absence of accurate models to predict liquid metal embrittlement oblige engineers to set up extensive test programs to determine an area of process parameters in which safe design is guaranteed. A qualitative understanding of the various influencing parameters during galvanizing is necessary to explain the occurrence of liquid metal embrittlement. This knowledge is also helpful to design an experimental test set up and procedure for evaluating the influence of one parameter where the effect of other parameters should remain constant. This master thesis deals with the occurrence of liquid metal embrittlement when galvanizing welded high strength steels. This paper gives an overview of the most important process parameters and gives a short description of possible future experimental work

Bone size and bone strength are increased in obese male adolescents

Context: Controversy exists on the effect of obesity on bone development during puberty. Objective: Our objective was to determine differences in volumetric bone mineral density (vBMD) and bone geometry in male obese adolescents (ObAs) in overlap with changes in bone maturation, muscle mass and force development, and circulating sex steroids and IGF-I. We hypothesized that changes in bone parameters are more evident at the weight-bearing site and that changes in serum estradiol are most prominent. Design, Setting, and Participants: We recruited 51 male ObAs (10-19 years) at the entry of a residential weight-loss program and 51 healthy age-matched and 51 bone-age-matched controls. Main Outcome Measures: vBMD and geometric bone parameters, as well as muscle and fat area were studied at the forearm and lower leg by peripheral quantitative computed tomography. Muscle force was studied by jumping mechanography. Results: In addition to an advanced bone maturation, differences in trabecular bone parameters (higher vBMD and larger trabecular area) and cortical bone geometry (larger cortical area and periosteal and endosteal circumference) were observed in ObAs both at the radius and tibia at different pubertal stages. After matching for bone age, all differences at the tibia, but only the difference in trabecular vBMD at the radius, remained significant. Larger muscle area and higher maximal force were found in ObAs compared with controls, as well as higher circulating free estrogen, but similar free testosterone and IGF-I levels. Conclusions: ObAs have larger and stronger bones at both the forearm and lower leg. The observed differences in bone parameters can be explained by a combination of advanced bone maturation, higher estrogen exposure, and greater mechanical loading resulting from a higher muscle mass and strength

Sex steroids in relation to sexual and skeletal maturation in obese male adolescents

Background: Childhood obesity is associated with an accelerated skeletal maturation. However, data concerning pubertal development and sex steroid levels in obese adolescents are scarce and contrasting. Objectives: To study sex steroids in relation to sexual and skeletal maturation and to serum prostate specific antigen (PSA), as a marker of androgen activity, in obese boys from early to late adolescence. Methods: Ninety obese boys (aged 10-19 y) at the start of a residential obesity treatment program and 90 age-matched controls were studied cross-sectionally. Pubertal status was assessed according to the Tanner method. Skeletal age was determined by an x-ray of the left hand. Morning concentrations of total testosterone (TT) and estradiol (E2) were measured by liquid chromatographytandem mass spectrometry, free T (FT) was measured by equilibrium dialysis, and LH, FSH, SHBG, and PSA were measured by immunoassays. Results: Genital staging was comparable between the obese and nonobese groups, whereas skeletal bone advancement (mean, 1 y) was present in early and midadolescence in the obese males. Although both median SHBG and TT concentrations were significantly (P < .001) lower in obese subjects during mid and late puberty, median FT, LH, FSH, and PSA levels were comparable to those of controls. In contrast, serum E2 concentrations were significantly (P < .001) higher in the obese group at all pubertal stages. Conclusion: Obese boys have lower circulating SHBG and TT, but similar FT concentrations during mid and late puberty in parallel with a normal pubertal progression and serum PSA levels. Our data indicate that in obese boys, serum FT concentration is a better marker of androgen activity than TT. On the other hand, skeletal maturation and E2 were increased from the beginning of puberty, suggesting a significant contribution of hyperestrogenemia in the advancement of skeletal maturation in obese boys

Quantification of the amount of epsilon martensite in a Fe-Mn-Si-Cr-Ni shape memory alloy by means of electron backscatter diffraction

A

Structural and magnetic transformations in the Fe-Mn binary system

The phase transformations of five binary iron-manganese (Fe-Mn) alloys with manganese contents ranging from 1 to 21 weight percent have been characterized in the temperature range between room temperature and 1250 degrees C. Differential scanning calorimetry and dilatometry were used to experimentally characterize both the phases and magnetic transformation temperatures. X-ray diffraction and light optical microscopy were employed for the room temperature microstructure characterization. Depending on the manganese content of the alloy, three different crystal structures can be found: body centered cubic (bcc) (alpha/alpha '), face centered cubic (fcc) (gamma), and hexagonal compact (hcp) (epsilon). At manganese contents lower than 10% the phases present are the alpha/alpha ' (bcc) and gamma (fcc). Above similar to 10 weight percent manganese increasing amounts of epsilon (hcp) is formed at the expense of the body centered cubic structures, and no alpha/alpha ' (bcc) is observed for the 21 weight-percent manganese alloy

Improvement of the shape memory effect in Fe-based alloys by training

Shape recovery in iron-based shape memory alloys is known to be incomplete. Thermomechanical cycling or training is recognized to improve the shape memory effect. In the present work, different aspects of training are studied: the number of cycles, the amount of deformation and the annealing temperature. As the number of cycles increases, the epsilon martensite plates become thinner and within the different grains they tend to align in the same direction. Still, different variants are present. XRD measurements showed a strong increase in the E martensite volume from cycle 1 to cycle 2 and a slight decrease for further cycles. There exists an optimum deformation for obtaining stress induced E martensite which is reversibly transformable to austenite during annealing. When the amount of deformation is too low, the fraction of stress induced epsilon martensite is very low, therefore, the shape memory effect is small. If the deformation is too large, slip may occur and different E; martensite variants are formed, which hinders the reverse epsilon ->gamma transformation. The recovery annealing temperature is critical for obtaining a good shape memory, especially during training. The recovery annealing temperature of 400 degrees C is too low for completing the reverse transformation; annealing at 600 degrees C is most commonly used