F. Van den Abeele

Towards a social and context-aware multi-sensor fall detection and risk assessment platform

For elderly people fall incidents are life-changing events that lead to degradation or even loss of autonomy. Current fall detection systems are not integrated and often associated with undetected falls and/or false alarms. In this paper, a social- and context-aware multi-sensor platform is presented, which integrates information gathered by a plethora of fall detection systems and sensors at the home of the elderly, by using a cloud-based solution, making use of an ontology. Within the ontology, both static and dynamic information is captured to model the situation of a specific patient and his/her (in)formal caregivers. This integrated contextual information allows to automatically and continuously assess the fall risk of the elderly, to more accurately detect falls and identify false alarms and to automatically notify the appropriate caregiver, e.g., based on location or their current task. The main advantage of the proposed platform is that multiple fall detection systems and sensors can be integrated, as they can be easily plugged in, this can be done based on the specific needs of the patient. The combination of several systems and sensors leads to a more reliable system, with better accuracy. The proof of concept was tested with the use of the visualizer, which enables a better way to analyze the data flow within the back-end and with the use of the portable testbed, which is equipped with several different sensors.

The Schoch effect to distinguish between different liquids in closed containers

In different industrial branches, it is necessary to characterize liquids in closed containers. For small cans, accessibility to both sides is almost trivial. However, in industries in which larger containers are used, and especially in the dock industry, only one side is accessible practically; and damping often prevents through-transmission ultrasonic measurements or pulse echo techniques. It is known that built-in sensors can be used to determine density and wave velocity of liquids; but normally containers are not equipped with such sensors. It is also known that differences in the reflection coefficient at a solid-liquid interface can determine the density and sound velocity of liquids, but only if the difference in acoustical impedance between the solid and the liquid is small. For most containers this condition is not provided; therefore, a more sensitive method is needed. This paper reports simulations that show how identical containers, having different liquids inside, can be distinguished from one another by means of differences in the Schoch effect at a Lamb wave angle of incidence for harmonic-bounded ultrasonic beams.

Dynamic behaviour of high strength pipeline steel

The occurrence of a longitudinal crack propagating along a gas pipeline is a catastrophic event, which involves both economic losses and environmental damage. Hence, the fracture propagation control is essential to ensure pipeline integrity. The commonly used ductile fracture control strategy for the design of high pressure pipelines is the Battelle Two Curve Method. This approach stipulates that if there is a crack speed at a given pressure that exceeds the gas decompression velocity at the same pressure, propagation will occur. However, for high strength pipeline steels, this method does not yield conservative predictions, as the absorbed impact energy during a Charpy test no longer reflects the actual burst behaviour of the pipe. Enhanced toughness measures, like Crack Tip Opening Angle and instrumented Battelle Drop Weight Tear test are being proposed as alternative options. These emerging toughness tests are complemented by numerical simulations of ductile crack propagation and arrest. Most of these models are based on the computation of void growth, and account for the local softening of the material due to void growth and subsequent coalescence. The constitutive behaviour of the sound pipeline steel is often modelled as merely an elastoplastic law, measured under quasi-static conditions. However, both Charpy tests and Battelle tests are dynamic events, which require knowledge of the strain rate sensitivity of the pipeline material. In addition, very high strain rates can occur in the vicinity of a running crack in a high pressure gas pipeline. Hence, the constitutive model for the pipeline steel has to account for strain rate sensitivity. In this paper, Split Hopkinson Tensile Bar (SHTB) experiments are reported on high strength pipeline steel. Notched tensile test are performed at high strain rates, to assess the influence of both strain rate sensitivity and triaxiality on the response of the material. In addition, dynamic experiments are conducted at low temperatures (-70°C) to evaluate the ductility of pipeline steel under such severe conditions. The results allow discriminating between the effects of strain rate, triaxiality and temperature

Numerical simulation of HPT processing

The principle of achieving high strength and superior properties in metal alloys through the application of severe plastic deformation has been exploited in the metal processing industry for many decades. In this contribution finite element simulations are presented of the HPT process. As opposed to most studies in literature, in which rigid sample holders are considered, the real elasto-plastic behavior of the holders is modeled. The simulations show that during the compression stage, plastic deformation occurs in the holders: initially, at the outside boundary of the sample cavity and, at a later stage, underneath the centre of the sample. The latter region of plastic deformation is rapidly growing and has a non-negligible effect on the response of the sample. Major conclusion is that the sample holders, and more specific, their deformability is key for the conditions in the specimen. Indeed, it severely affects important parameters for both the microstructural changes in the sample material, such as the amplitude and distribution of the hydrostatic stress, and its final shape.

Buckling and Unstable Collapse of Seamless Pipes and Tubes

Deepwater pipelines and high pressure casing and tubing are prone to buckling and unstable collapse under compressive loading and external pressure. The most important parameters governing the unstable collapse behaviour of perfectly round pipes and tubes are the circumferential yield stress of the material, the Young’s modulus and the ratio of diameter over thickness (D/t). Initial imperfections in the geometric shape of the pipe, like wall thickness variations or ovality, can have a pronounced influence on the collapse resistance of a pipe. Local dents can reduce the collapse pressure significantly, and trigger propagating buckles along the line. In this paper, buckling and unstable collapse of seamless pipes and tubes are studied. First, collapse pressure experiments for High Collapse Casing grades L80HC and P110HC are presented, showing that the seamless pipe production at ArcelorMittal Tubular Products in Ostrava (Czech Republic) is under tight quality control and complies with the API standards. Then, the critical collapse pressure is calculated for different scenarios. Depending on the ratio of diameter to wall thickness, four regimes are identified: yielding collapse, followed by plastic collapse, a transition range, and finally elastic collapse. For each condition, closed form expressions are derived for the critical collapse pressures. In addition, simplified design equations are reviewed to quickly estimate the collapse pressure. Then, the influence of initial imperfections on the collapse resistance is studied. Both the effects of geometric imperfections (ovality and wall thickness eccentricity) and material properties (especially yield stress and residual stresses) are addressed. In the end, an enhanced design equation is proposed to predict the critical collapse pressure of dented seamless pipes. This equation is validated by collapse experiments, can account for different initial imperfections, and is valid for a wide range of D/t ratios.© 2010 ASME

Towards a Numerical Design Tool for Composite Crack Arrestors on High Pressure Gas Pipelines

One of the major challenges in the design of ultra high grade (X100) high pressure gas pipelines is the identification of a reliable crack propagation strategy. Ductile fracture propagation is an event that involves the whole pipeline and all its components, including valves, fittings, flanges and bends. Recent research results have shown that the newly developed high strength large diameter gas pipelines, when operated at severe conditions (rich gas, low temperatures, high pressure), may not be able to arrest a running ductile crack through pipe material properties. Hence, the use of crack arrestors is required in the design of safe and reliable pipeline systems. A conventional crack arrestor can be a high toughness pipe insert, or a local joint with higher wall thickness. Steel wire wrappings, cast iron clamps or steel sleeves are commonly used non-integral solutions. Recently, composite crack arrestors have enjoyed increasing interest from the industry as a straightforward solution to stop running ductile cracks. A composite crack arrestor is made of (glass) fibres, dipped in a resin bath and wound onto the pipe wall in a variety of orientations. In this paper, the numerical design of composite crack arrestors will be presented. First, the properties of unidirectional glass fibre reinforced epoxy are measured and the micromechanic modelling of composite materials is addressed. Then, the in-use behaviour of pipe joints with composite crack arrestors is covered. Large-scale tensile tests and four point bending tests are performed and compared with finite element simulations. Subsequently, failure measures are introduced to predict the onset of composite material failure. At the end, the ability of composite crack arrestors to arrest a running fracture in a high pressure gas pipeline is assessed.Copyright

Advances in high strain rate material testing

In this contribution, attention is focused on new developments and possibilities for advanced material testing using split Hopkinson bar setups. The possibility to test non-common materials (such as small diameter steel cords), and to generate more dimensional stress states (e.g. in a three-point-bending configuration) is outlined. In both tests very low amplitude signals have to be captured. Because measurement devices have become much more sensitive in recent years, these signals can now be measured with sufficient accuracy. Moreover, the technical specifications of high-speed imaging devices have improved tremendously. A technique to extract the deformation of a Hopkinson specimen from high-speed streak camera images—using geometrical Moire and phase shifting—will be presented. Other advances, made possible by the increased availability of numerical tools, are enhanced signal processing and/or data extraction techniques. Finally, a combined numerical/experimental method to exclude the influence of the specimen geometry on the stress-strain curves extracted from classical Hopkinson experiments is presented.