Secondary contact and admixture between independently invading populations of the Western corn rootworm, diabrotica virgifera virgifera in Europe

The western corn rootworm, Diabrotica virgifera virgifera (Coleoptera: Chrysomelidae), is one of the most destructive pests of corn in North America and is currently invading Europe. The two major invasive outbreaks of rootworm in Europe have occurred, in North-West Italy and in Central and South-Eastern Europe. These two outbreaks originated from independent introductions from North America. Secondary contact probably occurred in North Italy between these two outbreaks, in 2008. We used 13 microsatellite markers to conduct a population genetics study, to demonstrate that this geographic contact resulted in a zone of admixture in the Italian region of Veneto. We show that i) genetic variation is greater in the contact zone than in the parental outbreaks; ii) several signs of admixture were detected in some Venetian samples, in a Bayesian analysis of the population structure and in an approximate Bayesian computation analysis of historical scenarios and, finally, iii) allelic frequency clines were observed at microsatellite loci. The contact between the invasive outbreaks in North-West Italy and Central and South-Eastern Europe resulted in a zone of admixture, with particular characteristics. The evolutionary implications of the existence of a zone of admixture in Northern Italy and their possible impact on the invasion success of the western corn rootworm are discussed

EBW of nuclear pressure vessel steels

Part of the mission for the Nuclear Advanced Manufacturing Research Centre (Nuclear AMRC) is to develop, mature and deploy advanced manufacturing technologies in the nuclear manufacturing industry. Electron beam welding (EBW) is widely considered to be one of the game-changing technologies which could reduce pressure vessel fabrication lead time, unit cost and manufacturing risk, while maintaining or improving quality & component integrity. This paper presents development work for the use of EBW as a joining technique for nuclear pressure vessel (NPV) steel walls of up to 100 mm thickness. SA508 Grade 3 as well as the higher strength type SA508 4N with increased hardenability were investigated. It has been demonstrated that EBW has the capability of joining these sections in a single pass, with elementary microstructural and mechanical examinations underpinning the basic performance support for such capability. Two-thirds scale components, such as those typical of a Small Modular Reactor (SMR) have demonstrated this processing duty-cycle further with the joint being completed in 26 minutes. This work will strengthen the viability of EBW applied to primary circuit safety-critical components, and will support a future ASME III code case

Electron beam additive manufacturing at the Nuclear AMRC

The Nuclear AMRC was established in the UK as an arm of the University of Sheffield to support industry and secure contracts in the nuclear sector – a wide scope of activities including nuclear new build, plant operations and decommissioning & waste management systems. One of the key goals is to work with industry partners in reducing unit cost, fabrication time, and risk associated with traditional manufacturing processes, whilst also striving to improve quality and engage with the industry regulators. The Nuclear AMRC’s facility was designed to accommodate large component development programmes and is capable of producing demonstrator components, using an array of state-of-the-art fabrication & manufacturing solutions. Acknowledging the great potential of electron beam welding (EBW) for modern manufacturing the Nuclear AMRC operates 2 EBW facilities. One of them is the largest electron beam facility in the UK, with a vacuum chamber volume of 208 m3, allowing EBW of large scale components as required for nuclear manufacturing. The mobile 30 kW, 60 kV gun is attached to an x-y-z gantry via two rotary axes. These axes together with turn and tilt tables are all CNC controlled allowing a very flexible approach for welding of parts up to 100 tons with sizes up to 6 x 4 x 3 metres. In addition two wire feeders are attached to the gun opening the facility to additive manufacturing. Additive manufacturing achieves increasingly more acceptance for industrial applications. Electron Beam Additive Manufacturing (EBAM) exhibits a very efficient, high power energy source which easily couples with metals promising one of the highest deposition rates for all metal additive manufacturing technologies. The processing in high vacuum is ideal for reactive alloys. CNC is standard for most of the EBW set-ups allowing easy application of an automated build strategy. This paper aims to present EBAM builds realised at the Nuclear AMRC demonstrating the ability to achieve complex structures for different materials

Time-economic lifetime assessment for high performance thermal barrier coating systems

Strategies for time-economic lifetime assessment of thermal barrier coatings (TBC) in service are described and discussed on the basis of experimental results, achieved on material systems with coatings applied by electron beam physical vapour deposition. Service cycles for gas turbine blades have been simulated on specimens in thermo-mechanical fatigue tests, accelerating the fatigue processes by an increase of load frequency. Time dependent changes in the material system were imposed by a separate ageing, where the samples were pre-oxidized prior to the fatigue test. Results of thermo-mechanical fatigue tests on pre-aged and as-coated specimens gave evidence of interaction between fatigue and ageing processes. An alternative approach is used, which is focused on the evolution of a failure relevant damage parameter in the TBC system. The interfacial fracture toughness was selected as a damage parameter, since one important failure mode of TBCs is the spallation near the interface between the metal and the ceramic. Fracture mechanical experiments based on indentation methods have been evaluated for monitoring the evolution of the interfacial fracture toughness as a function of ageing time. It was found that the test results were influenced by both changes of the interface (which is critical in service) and changes in the surrounding material.status: publishe