Efficient fatigue testing of tubular joints

Tubular joints are intensively used in off-shore structures for shallow waters. Depending on the sea conditions and the type of structure, the design can be fatigue driven. This is particularly the case for off-shore wind turbines, where turbulences are generating a fatigue loading. Any improvement of the fatigue performance of the tubular joint would be beneficial to reduce the weight and the cost of the structure. To assess efficiently the fatigue resistance of the tubular joint, a testing method has been developed based on the resonance principle. The complete circumference of the welded joint can be loaded, successively in the in-plane and out-of-plane modes at a frequency close to 20hz. Finite element computations were used to investigate the feasibility of the concept. Then, an X-node was made and successfully tested to investigate the stress distribution along the weld. The experimental results were compared with finite element computations, giving a good agreement

Sustainable control of internal fruit rot in bell peppers (Capsicum Annuum L.)

Since 2003, Belgian bell pepper growers are confronted with a new disease called internal fruit rot, which is caused by Fusarium species. The pathogen infects the fruit via the flowers and stays latent until ripening or even post harvest, after which fungal mycelium can develop and cause an internal and later external fruit rot. About 75% of the isolates obtained from diseased peppers belong to the Fusarium lactis species complex (FLASC) while F. oxysporum and F. proliferatum were less frequently isolated, 14% and 9%, respectively. The pathogenicity of these three Fusarium species was compared on two to four cultivars using assays involving fruit as well as flower inoculation. Differences in pathogenicity between the Fusarium species were most clearly observed after fruit inoculation, but these were not consistent with the results of flower inoculation, which is considered more representative. To better understand the latent phase of the infection process, and especially to investigate if there is a decline in the number of latent infections during the growing period, we determined the presence of Fusarium in the flowers and fruit at 10 time points between flowering and harvest using traditional surface disinfection and plating techniques using either natural infection or artificially inoculated (FLASC) flowers. This experiment was repeated at least three times during the growing season. To our surprise, the frequency of latently infected fruit stayed at a similar level during the entire growing process, indicating that there may be only limited opportunities to affect the amount of disease after the initial infection took place. One method to reduce the number of initial infections may be to remove the withering tissue such as the pistil and petals, as preliminary research showed these were saprophytically colonized with FLASC isolates. Such removal proved not successful in several experiments, indicating the infection process is quite fast and the number of airborne spores is insufficiently lowered by removal of these structures. Our study provided more insights into this pathosystem, which may result in opportunities for the sustainable control of internal fruit rot via prevention of flower infection and screening for disease resistance.status: publishe

Advanced plasticity modeling for ultra-low-cycle-fatigue simulation of steel pipe

Pipelines and piping components may be exposed to extreme loading conditions, for instance earthquakes and hurricanes. In such conditions, they undergo severe plastic strains, which may locally reach the fracture limits due to either monotonic loading or ultra-low cycle fatigue (ULCF). Aiming to investigate the failure process and strain evolution of pipes enduring ULCF, a lab-scale ULCF test on an X65 steel pipeline component is simulated with finite element models, and experimental data are used to validate various material modeling assumptions. The paper focuses on plastic material modeling and compares different models for plastic anisotropy in combination with various hardening models, including isotropic, linear kinematic and combined hardening models. Both isotropic and anisotropic assumptions for plastic yielding are considered. As pipes pose difficulty for the measurement of plastic properties in mechanical testing, we calibrate an anisotropic yield locus using advanced multi-scale simulation based on texture measurements. Moreover, the importance of the anisotropy gradient across thickness is studied in detail for this thick-walled pipeline steel. It is found that the usage of a combined hardening model is essential to accurately predict the number of the cycles until failure, as well as the strain evolution during the fatigue test. The advanced hardening modeling featuring kinematic hardening has a substantially higher impact on result accuracy compared to the yield locus assumption for the studied ULCF test. Cyclic tension-compression testing is conducted to calibrate the kinematic hardening models. Additionally, plastic anisotropy and its gradient across the thickness play a notable, yet secondary role. Based on this research, it is advised to focus on improvements in strain hardening characteristics in future developments of pipeline steel with enhanced earthquake resistance.status: publishe

Sustainable control of internal fruit rot in bell pepper: A multidisciplinary approach

An internal fruit rot disease of sweet peppers, first reported in Canada in 2000, later emerged as a significant disease of greenhouse-grown bell pepper worldwide. It is caused primarily by members of the Fusarium lactis species complex (FLASC) and to a lesser extent by Fusarium oxysporum and Fusarium proliferatum. After infection via the flowers, the fungus stays latent in the fruit until maturity. During ripening, the fungus starts to proliferate on the inside of the fruit. Later, sunken lesions appear on the outside. Nearly all growers are confronted with this problem to some extent, with an average annual yield loss estimated at 5% and seasonal peaks up to 20%. Despite the importance of the disease, particularly during years with high disease incidence, efficient control is lacking. A multidisciplinary approach is clearly needed. Here we report on the potential use of Biological Control Agents (BCA) and plant resistance elicitors as well as susceptibility trials of pepper varieties. Seven BCAs were active in vitro. These were tested under conventional greenhouse conditions. First, one-dayold flowers were separately inoculated with BCAs. One day later they were inoculated with FLASC. The infection incidence in two-week-old fruits and mature fruits was determined using surface disinfection and plating techniques. Two BCA isolates (one commercially available and one KUL isolate) reduced the number of infected fruits by 50%. Another strategy to reduce the initial infection of the flowers was tested, i.e. inducing plant resistance using elicitors. Three commercial elicitors were tested twice under greenhouse conditions and applied at recommended dose. The infection incidence was determined at 4 time points during fruit development. Surprisingly, no decline in the infection rate was observed. To evaluate the difference in susceptibility between pepper varieties, fruits of 12 varieties were pin-wounded and inoculated with a mycelium plug of FLASC. The lesion size on the yellow varieties was significantly larger than those on the red varieties. In addition, controlled in situ flower inoculations with FLASC were conducted on different varieties. Fruit infection was determined two weeks after inoculation and at harvest. Red and yellow cultivars were equally susceptible to infection but the final percentage of symptomatic fruit was significantly different between some varieties. Although no variety showed complete resistance, some had significantly less disease. The results were consistent with those of the previous year, suggesting these assays may give a good indication of varietal susceptibility. These studies showed that both BCAs and pepper variety can contribute to the multidisciplinary control of Fusarium internal fruit rot. When used with other measures (e.g. climatic control) yield loss may be reduced to a commercially acceptable level. Keywords: Capsicum annuum, BCA, elicitor, varietal susceptibilitystatus: publishe

Internal fruit rot (Fusarium spp.) of Greenhouse Bell Peppers

Since 2003 the cultivation of bell peppers in Belgium has to deal with a new disease that leads to internal fruit rot and is caused by Fusarium species. Infection takes place in the flowering stage. The pathogen stays latent during the growth of the fruit after which fungal mycelium can develop during ripening, but mostly after harvest, causing internal and later external fruit rot. Around 75% of the isolates obtained from diseased fruits belonged to the Fusarium lactis species complex (FLASC). F. oxysporum and F. proliferatum were also isolated but less frequently, 14% and 9% respectively. The pathogenicity of these Fusarium species was studied in assays using fruit as well as flower inoculation on different cultivars. Differences in pathogenicity were most clearly observed after fruit inoculation. These results however were not consistent with the results of flower inoculation, which is considered more representative, that showed only very little difference between the Fusarium species. Furthermore there was also an impact of the cultivar on the development of internal fruit rot. To gain a better insight in the latent phase of the infection process and particularly to study the development of the frequency of latent infections during the growing period of the fruit an experiment was set up and repeated three times over the course of the growing season. The presence of Fusarium in the flowers and in the fruits was determined at several time points between flowering and harvest using traditional surface disinfection and plating techniques using either natural infection or artificially inoculated (FLASC) flowers. The frequency of latently infected fruits stayed at a similar level from flower to harvest, indicating only very limited opportunities to affect the disease after initial infection took place. Preventing initial infection will thus be an important factor in the control of internal fruit rot. One way to reduce the amount of initial infections may be the removal of withering tissues such as pistil and petals, as preliminary results have shown that these were frequently saprophytically colonized with FLASC isolates. Several experiments indicated however that such removal was not successful, suggesting that the infection process is quite fast and that the number of airborne spores is insufficiently lowered by the removal of withering flowering structures. As our study to gain more insights into this pathosystem goes on, opportunities for sustainable control of internal fruit rot, such as prevention of flower infection by biological control agents, and screening for disease resistance, are being explored.status: publishe

Birth of the first ICSI foal in the Benelux

This paper describes the birth of the first intracytoplasmic sperm injection (ICSI) foal in the Benelux. Oocytes were aspirated from ovaries from slaughtered mares. After in vitro maturation, the oocytes were fertilized by ICSI and cultured in vitro for 9 days. Two embryos reached the blastocyst stage and they were transferred to the uterus of a synchronized mare. Six days later a single embryonic vesicle was diagnosed by ultrasound. After a normal pregnancy a healthy foal was born on the 27(th) of October 2009. Parentage testing via microsatellite genotyping confirmed that the foal originated from the transferred embryo