Calibration Procedures for a Computational Model of Ductile Fracture

A recent extension of the Gurson constitutive model of damage and failure of ductile structural alloys accounts for localization and crack formation under shearing as well as tension. When properly calibrated against a basic set of experiments, this model has the potential to predict the emergence and propagation of cracks over a wide range of stress states. This paper addresses procedures for calibrating the damage parameters of the extended constitutive model. The procedures are demonstrated for DH36 steel using data from three tests: (i) tension of a round bar, (ii) mode I cracking in a compact tension specimen, and (iii) shear localization and mode II cracking in a shear-off specimen. The computational model is then used to study the emergence of the cup-cone fracture mode in the neck of a round tensile bar. Ductility of a notched round bar provides additional validation.Engineering and Applied Science

Agrobacterium vitis strains lack tumorigenic ability on in vitro grown grapevine stem segments

Grapevine stem segments were cocultivated with three different Agrobacterium tumefaciens and three different A. vitis strains. A. tumefaciens strains induced tumors at variable frequencies, while A. vitis-infected stem segments never formed crown galls. The tumorous nature of tissues grown on hormone free medium was confirmed by opine assays. Bioinformatic and PCR analysis of the virulence regions of various A. tumefaciens and A. vitis Ti plasmids showed that virH2 and virK genes are common in A. tumefaciens but they are lacking from A. vitis. Thus virH2 and virK genes may be essential for grapevine stem segment transformation, but expression of certain T-DNA genes of A. vitis may also prevent the growth of transformed cells. Our data indicate that the tumorigenic ability of A. vitis is different on intact plant and on their explants, and that the specific host association of A. vitis on grapevine is probably determined by physiological and biochemical factors (e. g., better colonizing ability) rather than by its increased tumorigenic ability. Therefore it is not reasonable to develop „helper” plasmids for grapevine transformation from A. vitis pTis, unless their avirulence on in vitro explants is determined by T-DNA gene(s). Due to the inability of A. vitis to induce tumors on grapevine stem segments, the use of in vitro explant assays cannot be reliably used to select A. vitis resistant grapevine genotypes or transgenic lines

Gendered Social Policies in (Post-)Communist Countries: The Case of Poland

The conservative “backlash” of the 1980s did not only apply to women’s rights but also to social policies. It was often perceived as a phenomenon of the so-called “first world”. However, current historical research on state-socialist countries shows that it could also be observed in these particular countries, for example in social policies in communistPoland. There, a new government under the leadership of Edward Gierek came into power in 1970 and tried, on the one hand, to modernize the economy in an effort to improve its international competitiveness. On the other hand, the new leadership also tried to build a “second Poland” by raising the standard of living. Social policies became an important tool to ensure communist preservation of power at that time. However, this, in the end failed, attempt to modernize Poland led to a (re-)traditionalization of family life and gender relations. Ultimately, this meant that the government tried to remove women from the labour market. This was closely connected to a discourse on a “crisis of demography” that became prominent during the 1970s and influenced subsequent governments regarding their social policies. The article analyses these developments in social policies in Communist Poland and situates them in a wider context by looking at the first years of transformation in the 1990s. It will therefore highlight continuities and fractions in this particular political field between late and post-communism

THE RISE OF THE SUPER-ATHLETES, AND WHY THERE IS NO TURNING BACK

Born and raised in Beirut, bio-medical engineer Mounir is the co-founder and Managing Director of N3XT Sports Inc. A world citizen who is passionate about sports, technology, entrepreneurship, and innovation, he has 15+ years’ experience in various positions in the sports industry, the latest of which was Director of Technology and Innovation at the US Olympic Committee; he also sits on the working board of Women in Sports Tech. Mounir holds a PhD in Bioengineering, is fluent in four languages, and has recently moved with his wife and two children from the Silicon Valley to Barcelona. Mounir‘s expertise areas of wearable technology, smart textiles and fabric, Internet of Things (IoT), artificial intelligence and cognitive computing are of interest to sports biomechanists in their goal of improving sports performance. Mounir has extensive experiences creating, managing and advising technology start ups and with the US Olympic team. Mounir‘s keynote will stimulate biomechanists to think of new ways to help improve athlete’s results with technology

Fragmentation, sliding and interface degradation in SiC/SiC composites

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In-situ 3D visualization of composite microstructure during polymer-to-ceramic conversion

One route for producing fiber-reinforced ceramic-matrix composites entails repeated impregnation and pyrolysis of a preceramic polymer in a fiber preform. The process relies crucially on the development of networks of contiguous cracks during pyrolysis, thereby allowing further impregnation to attain nearly-full densification. The present study employs in-situ x-ray computed tomography (XCT) to reveal in three dimensions the evolution of matrix structure during pyrolysis of a SiC-based preceramic polymer up to temperatures of 1200°C. Observations are used to guide the development of a taxonomy of crack structures and to identify the temporal hierarchy of their formation. A quantitative analysis is employed to characterize effects of local microstructural dimensions on the conditions required to form cracks of various types. Complementary measurements of gas evolution and mass loss of the preceramic polymer during pyrolysis as well as changes in mass density and Young\u27s modulus provide context for the physical changes revealed by XCT. The findings provide a foundation for future development of physics-based models to guide composite fabrication processes

Comportamiento de yautía [Xanthosoma sagittifolium (L.) Schott] derivada de cultivo de tejido

To respond to questions raised about field adaptability of tissue culture derived (TC) cocoyam, a study was conducted to compare TC cocoyam with cocoyam from non-tissue culture (NTC), i.e., vegetatively propagated. Throughout the vegetative cycle, TC plants out performed NTC plants in terms of plant vigor and average leaf number. In general, TC plants acclimatized in the greenhouse produced significantly more suckers than NTC plants, regardless of the period within the growing season. In the trial, the average number of cormels per plant varied from 6.66 to 12.44. TC plants acclimatized for two months (h1), yielded higher than the other TC and TCN plants. The total weight (weight of cormels and corms) of TC plants of h1 was significantly higher than in all other treatments. This finding suggests the importance of the acclimatization process in preparing TC derived plantlets for field conditions.Para responder a preguntas sobre la adaptabilidad al campo de la yautía derivada de cultivo de tejido (CT), se comparó ésta con ia yautía no derivada de cultivo de tejido (NCT). Durante el ciclo vegetativo, las plantas CT superaron a las plantas NCT en términos de vigor de la planta y del número promedio de hojas. Por lo general, las plantas CT aclimatadas en el invernadero produjeron significativamente más hijuelos que las plantas NCT, sin importar la etapa de crecimiento de !a planta. El número promedio de cormelos por planta varió de 6.66 a 12.44. Las plantas CT aclimatadas por dos meses (h1) produjeron más cormelos que las otras plantas CT y que las plantas NCT. El peso total (peso de los cormelos y los cormos) de las plantas CT en h1  fue significativamente mayor que el peso total obtenido en los otros tratamientos. Este hallazgo sugiere la importancia del proceso de aclimatización en la preparación de las plantas derivadas de cultivo de tejido para las condiciones del campo