Previous Test Series Research Articles

The influence of R/t-ratio on the imperfection sensitivity of the buckling load of thin-walled CFRP cylindrical shells

Thin-walled cylindrical shells under axial compression load are prone to buckling. The influencing factors leading to a reduction of the buckling load are a major design challenge. The sensitivity to imperfection increases with rising slenderness. In literature, cylinders with the same parameters and different slenderness are rarely tested in a larger number of samples. In this contribution, seven cylindrical shells, six of them nominally identical, are tested on two different test rigs and compared with twelve specimens with a smaller radius and same wall thickness from a previous series of tests. It is shown how the imperfection sensitivity is dependent on the R/t-ratio. Additionally, it is demonstrated how the quality of the test set ups corresponds with the achieved buckling load. Finally, the suitability of selected design approaches is determined based on the test results. Based on that, recommendations for the choice of a suitable approach are given.

Flow adaptive aerodynamic probe for turbomachinery flows

In order to enable turbomachinery research to obtain data highly resolved in space and time, a novel flow adaptive aerodynamic probe concept has been developed and presented in this paper. The algorithm selects the measurement positions of the probe automatically and therefore provides higher measurement fidelity compared to traditional methods. The development of the adaptive algorithm has been done in several steps. First an automatic 1Dtraversing algorithm has been developed. The following steps dealt with the subject of a 2D adaptive flow concept development, whereas primarily visual programming language-computer package simulations of the new 2D algorithm have been done based on data from previous test series at the Turbomachinery Laboratory. The new 2D traversing algorithm is fully selfcontrolled and requires minimal input such as blade count and hub and tip diameters. Furthermore, areas of interest (e.g. secondary flows, wake) are detected automatically and higher measuring point resolutions are ensured in these regions. After the successful simulations, the intelligent 2D algorithm has been adapted to an object oriented programming environment used for automated data acquisition and reduction. An evaluation of the flow adaptive aerodynamic flow concept has been done on a pressure turbine facility by means of a steady pneumatic probe. The measurement results show that the new 2D algorithm has the potential to detect new flow phenomena. In contrast to traditional algorithms, which in case of a possible enhancement demand a knowledge of the position of interesting areas such as the wake and vortical structures before starting the measurement, the new algorithm detects the right areas and enhances the resolution fully self controlled in these areas. Furthermore, the new 2D flow adaptive probe concept shows a significant improvement regarding the needed time for one measurement.

Investigations on the Triboelectrostatic Charging Behaviour and the Triboelectrostatic Sortability of Different Oxides

In the course of this study, several test series were carried out to investigate the triboelectrostatic charging behaviour of various oxides. At the beginning, the influence of the degree of aging and the influence of the sample storage on the charging efficiency of the oxide samples was analysed. For this purpose, two oxide samples were stored under different environmental conditions and then sorted using triboelectrostatic belt separation. Results of a previous series of tests showed that an increased feed temperature has a negative effect on the charging behaviour of calcium and magnesium oxide. Therefore, the effects of a reduced feed temperature were also examined. For these experiments, samples were stored at 8 °C under exclusion of air. In addition, a series of tests was carried out with a gradual increase of the voltage on the triboelectrostatic belt separator in order to determine possible differences in the charging efficiency of calcium oxide and magnesium oxide and to subsequently use them for the separation.

Occupant Restraint in Far-Side Impacts: Cadaveric and WorldSID Responses to a Far-Side Airbag

Previous studies indicate that seatbelts may require supplementary restraints to increase their effectiveness in far-side impacts. This study aimed to evaluate the effectiveness of a novel, far-side-specific airbag in restraining and preventing injuries in far-side impacts, and to evaluate the WorldSID's response to the presence of a far-side airbag. A series of tests with three Post-Mortem Human Subjects and the WorldSID was conducted in a vehicle-based sled environment equipped with a far-side airbag. Results of these tests were evaluated and compared to a previous test series conducted without the airbag. All of the PMHS retained the shoulder belt on the shoulder. The airbag significantly reduced PMHS injury severity and maximum lateral head excursion. While the WorldSID exhibited a similar decrease in lateral excursion, it was unable to represent PMHS thoracic deflection or injury probability, and it consistently slipped out of the shoulder belt. This indicates that the WorldSID is limited both in its ability to evaluate the effect of changes in the seatbelt system and in its ability to predict thoracic injury risk and assess airbag-related injury mitigation countermeasures.

Proof of Concept for Ozone-Based Disinfection of Heater Cooler Units

Abstract Heater Cooler Units (HCUs) are frequently used not only during heart surgery but also in ECMO therapy to regulate the blood temperature of patients. It is known from cardiac surgery that the water circuits of HCUs can be bacterially contaminated and under adverse conditions can lead to a nosocomial infection of the patient. The addition of chemical disinfectants to the water of HCUs is problematic. In addition, it is an increasingly significant cost factor due to the required material and personnel input. The aim of this research project is both the development of an automated device for disinfecting water in HCUs and proof of its effectiveness. The device is based on ozone, a substance with known antimicrobial properties. To prevent ozone from coming into contact with the HCU components, the water is irradiated with UV light (254nm). Two bypasses and ozone sensors guarantee a complete elimination of residual ozone. The effectiveness of the device was tested by series of experiments with the surrogate germ, Pseudomonas aeruginosa. The device allows a wide range of ozone concentrations and exposure times to be selected. In previous test series, it has been shown both that a reduction of the bacterial count to drinking water quality can be achieved with a treatment time of only one hour, and that self-cleaning can be carried out effectively before clinical use, and in standby mode. Attention must be paid to the water quality in HCUs as a potential source of infection, regardless of where they are used. The "proof of concept" showed an excellent disinfection effect with simultaneous elimination of excess ozone to drinking water levels. The number of indicator bacteria in the water tank of the dummy HCU was reduced by approx. 98% after only 30 minutes.

Cyclic Behavior of Lap Splices Strengthened with Ultrahigh Performance Fiber-Reinforced Concrete

The cyclic behavior of six full-scale reinforced concrete (RC) beams with a deficient lap splice strengthened with ultra-high-performance fiber-reinforced concrete (UHPFRC) is experimentally investigated. The experimental program is based on the findings of previous test series carried out in the same research program that demonstrated the ability of UHPFRC to eliminate bond failure in deficient lap splices of beams and wall-type bridge columns. The objective of this experimental work is to determine the efficiency of this strengthening technique on wide flexural elements (beams, slabs, walls, or wall columns) subjected to reverse cyclic loading. Specimen reinforcement consists of two pairs of deformed bars spliced at midspan on both tension and compression faces. The strengthening technique consists of replacing normal concrete around lapped bars in the splice region by UHPFRC, which allows for keeping the original member geometry. One type of fiber, three fiber contents, two bar diameters, and two bar arrangements are considered. For isolating the UHPFRC contribution, the splice regions are free of any confinement. The beam specimens are tested at four points, bending with a constant-moment region along the splice length. The result indicates that UHPFRC with a fiber content of 2 or 3% can significantly increase the bond strength of splice bars without confinement. The levels of ductility reached for the highest fiber content meet the requirements for high ductility demand, such as in seismic design. The results demonstrate that an appropriate casting method combined with a self-compacting UHPFRC with an appropriate fiber content ensure the efficiency of the strengthening technique for providing for the continuity of lapped bars and for enabling a high ductility capacity under monotonic or cyclic loading. The results also confirm the applicability of the method for strengthening lap-spliced regions of wide elements—such as slabs, shear walls, and wall-bridge piers—without having to provide any confinement.

Experimental investigation on punching resistance of R-UHPFRC–RC composite slabs

An effective method to strengthen existing reinforced concrete (RC) structures is to add a thin layer of ultra-high performance fiber reinforced cement-based composite (UHPFRC), with or without steel rebars, over the concrete slab to create a composite element. It was demonstrated by previous test series that this method increases rigidity, bending and shear strength of one-way RC members. This paper presents the results of punching tests on six composite slabs without transverse reinforcement. The parameters of the tests included the thickness of the UHPFRC layer and the amount of reinforcement in it. All slabs failed in punching mode with a drop in resistance after the maximum resistance was measured. For a layer of 50 mm of UHPFRC, the normalised resistance was at least 1.69 times greater than the normalised resistance of the RC reference slab. The layer of UHPFRC increased the rigidity of the slab and provided added shear resistance to the cracked RC section by out of plane bending. By doing so, it allowed more deformation to take place in the RC section before punching failure. This results in rotations and deflections at maximum resistance similar to what was observed for the reference RC slab.

Quantification of Slab Influences on the Dynamic Performance of RC Frames against Progressive Collapse

AbstractNumerous studies have indicated that the practice of ignoring the contribution of reinforced concrete (RC) slab in resisting progressive collapse is overconservative; however, the extent of influence of a slab, especially in terms of dynamic responses, have been rarely studied. To quantify this effect, two series of RC beam–column substructures (named DS and DF in this paper), with and without slab respectively were subjected to a series of dynamic tests involving the sudden removal of a corner support. To further elucidate the dynamic response of RC frames against progressive collapse, the experimental data acquired in this study were compared with their respective static responses derived in a previous series of tests published in another paper. The dynamic effects were evaluated by the newly defined term dynamic load increase factor (DLIF), which was defined as the ratio of static ultimate strength (SUS) to dynamic ultimate strength (DUS). The SUS of the test specimens had been captured in thei...

Assessment of the in vivo biomechanical properties of the human uterine cervix in pregnancy using the aspiration test: A feasibility study

Objective To date no diagnostic tool is yet available to objectively assess the in vivo biomechanical properties of the uterine cervix during gestation. Methods We show the first clinical application of an aspiration device to assess the in vivo biomechanical properties of the cervix in pregnancy with the aim to describe the physiological biomechanical changes throughout gestation in order to eventually detect pregnant women at risk for cervical insufficiency (CI). Results Out of 15 aspiration measurements, 12 produced valid results. The stiffness values were in the range between 0.013 and 0.068 bar/mm. The results showed a good reproducibility of the aspiration test. In our previous test series on non-pregnant cervices our repetitive measurements showed a standard deviation of >20% compared to <±10% to our data on pregnant cervices. Stiffness values are decreasing with gestational age which indicates a progressive softening of cervical tissue towards the end of pregnancy. Three pregnant women had two subsequent measurements within a time interval of four weeks. Decreasing stiffness values in the range of 20% were recorded. Discussion This preliminary study on the clinical practicability of aspiration tests showed promising results in terms of reproducibility (reliability) and clinical use (feasibility). Ongoing studies will provide further insights on its usefulness in clinical practice and in the detection of substantial changes of the cervix in pregnancy indicative for threatened preterm birth or cervical insufficiency.

Strength of Headed Stud Shear Connection in Composite Beams

The paper summarises the results of an extensive review of various push-out test series in order to determine the mean strength of headed stud shear connectors in solid slab applications. It also investigates the influence that different test set-ups can have on the connector strength. Based on the findings, an analysis of previous test series of stud shear connection incorporating trapezoidal steel decking is undertaken which indicates the unreliable and unconservative nature of the reduction factor approach.

Anchorage Length of Near-Surface Mounted Fiber-Reinforced Polymer Bars for Concrete Strengthening—Experimental Investigation and Numerical Modeling

Near-surface mounted (NSM) fiber-reinforced polymer (FRP) bars are being increasingly recognized as a valid alternative to externally bonded FRP laminates for enhancing flexural and shear strength of deficient concrete, masonry, and timber members. The ultimate capacity and service performance of strengthened members are deeply impacted by bond characteristics of the strengthening system on which, in the case of NSM bars, limited data is available. This paper follows up on prior investigations into the mechanics of bond of NSM bars to concrete. Experimental results completing a previous test series are reported and discussed, and a global evaluation of results of 3 different test series is attempted. A 3-D finite element model for bond of NSM reinforcement is proposed and calibrated on the basis of some experimental findings.

CENTRIFUGE TESTING OF MODEL MASONRY ARCH BRIDGES.

The effect of gravity is fundamental in the behaviour of masonry arch bridges, but previous laboratory testing of scale model arches has ignored its effect. A series of centrifuge tests on scale models constructed using real masonry materials is described - the first model arch bridges to be tested in a correctly scaled gravity field. The test geometry was chosen to enable direct comparison with a previous series of tests on 3 m span arches carried out under laboratory conditions. The failure mechanisms, stiffness and scaled failure loads are compared with those of the prototype tests. The test programme demonstrates that centrifuge modelling is a valuable technique, considerably extending the usefulness of model testing in masonry research. (A)

Limit Analysis of Welded Tee End Connections for Hollow Tubes

This paper presents a limit analysis, based on the yield line approach, for predicting the ultimate capacity of welded tee end connections for hollow tubes. Five failure mechanisms are identified. The failure mechanisms range from simple mechanisms such as yielding of the cleat plate or the tube, to the more complex mechanisms involving a combination of hinge formation in the cap plate and local yielding in the tube. It is shown that the dimensions of the connection components involving the tube, the cap and the cleat plate sizes determine which is the controlling failure mechanism. Results presented are applicable to welded tee end connections for hollow tubes of both circular and rectangular sections. A previous series of tests on this type of end connection was conducted on tubes of circular hollow section. A further series of tests on tubes of square hollow section is presented. The theoretical prediction, based on the yield line approach, agree very well with test results from 36 welded tee end connections on circular and square hollow tubes.

Experimental study of the Dissolution of spent fuel at 85°C in Natural Ground Water

AbstractSemi-static dissolution tests using pressurized water reactor spent fuel rod segments and NNWSI reference J-13 well water in sealed stainless steel vessels at 85°C are being conducted in support of the Waste Package Task of the NNWSI Project. Test specimens include: bare fuel plus the empty cladding hulls, fuel rod segments with artificially induced cladding defects and water-tight end caps, and undefected fuel rod segments with water-tight end caps. The test conditions approximate those expected in the proposed NNWSI Project repository when the waste package has cooled sufficiently to allow water to enter a breached container and contact the fuel rods, some of which may exhibit various degrees of cladding failure. Periodic solution samples (unfiltered and filtered) were analyzed for most radionuclides for which cumulative release limits are listed by the U.S. Environmental Protection Agency. Results from the first six-month cycle of the 85° C tests are presented and are compared with results from the first cycle of a previous test series run at 25° in fused silica test vessels.

Macroscopic static and dynamic mechanical properties of Yule marble

The static and dynamic tensile and compressive properties of Colorado Yule marble have been obtained from samples all secured from the same parent slab. Specimens were cored in the three principal directions of this transversely isotropic material, the axis of symmetry having been determined petrographically. Standard quasi-static and creep tests were performed, and both Hopkinson-bar and split-Hopkinson-bar tests were conducted for the collection of data at higher loading rates. Elastic constants evaluated for the material on the basis of the present investigation were compared with corresponding static and dynamic values from a previous series of tests conducted on a large block of Yule marble, and to dynamic constants for the same block determined in a separate investigation by means of wavespeed data secured from embedded crystal transducers. The behavior of Yule marble does not seem to conform to any well-known constitutive relation and is, thus, most easily characterized by suitable sets of experimental data.

VISUAL SEARCH PERFORMANCE IN MOVING STRUCTURED FIELD.

The performance of 16 male observers who searched for an incomplete ring (Landolt C) among a number of solid rings in a square, moving field was measured. Search performance deteriorated as velocity or object density was increased; a target was more likely to be detected the closer it was to the center of the field; there was no significant correlation between the age of the observer and his search performance; there was significant correlation between foveal visual acuity and search performance in the moving field. The performance of the same observers on a previous series of tests is compared to their performance on the tests reported here. A hypothesis concerning the role of peripheral and foveal vision in searching for targets is advanced.