scholarly journals On the Use of Ultrasound Waves to Monitor the Local Dynamics of Friction Joints

2019 ◽  
Vol 60 (1) ◽  
pp. 129-141
Author(s):  
L. Pesaresi ◽  
A. Fantetti ◽  
F. Cegla ◽  
L. Salles ◽  
C.W. Schwingshackl
Keyword(s):  
Numerical Models ◽  
Test Procedure ◽  
Contact Interface ◽  
Stick Slip ◽  
Local Dynamics ◽  
Ultrasound Waves ◽  
Preliminary Study ◽  
Initial Results ◽  
Nonlinear Nature ◽  
Validation Experiments

Abstract Friction joints are one of the fundamental means used for the assembly of structural components in engineering applications. The structural dynamics of these components becomes nonlinear, due to the nonlinear nature of the forces arising at the contact interface characterised by stick-slip phenomena and separation. Advanced numerical models have been proposed in the last decades which have shown some promising capabilities in capturing these local nonlinearities. However, despite the research efforts in producing more advanced models over the years, a lack of validation experiments made it difficult to have fully validated models. For this reason, experimental techniques which can provide insights into the local dynamics of joints can be of great interest for the refinement of such models and for the optimisation of the joint design and local wear predictions. In this paper, a preliminary study is presented where ultrasound waves are used to characterise the local dynamics of friction contacts by observing changes of the ultrasound reflection/transmission at the friction interface. The experimental technique is applied to a dynamic friction rig, where two steel specimens are rubbed against each other under a harmonic tangential excitation. Initial results show that, with a controlled experimental test procedure, this technique can identify microslip effects at the contact interface.

PRELIMINARY STUDY ON NOVEL BEAM-TO-COLUMN CONNECTION BASED ON SMA PLATE

2021 ◽  
Vol 8 (1) ◽  
Author(s):  
Michael CH Yam ◽  
Ke Ke ◽  
Ping Zhang ◽  
Qingyang Zhao
Keyword(s):  
Friction Coefficient ◽  
Energy Dissipation ◽  
Numerical Study ◽  
Numerical Models ◽  
Numerical Technique ◽  
The Self ◽  
Hysteretic Behavior ◽  
The Novel ◽  
Energy Dissipation Capacity ◽  
Preliminary Study

A novel beam-to-column connection equipped with shape memory alloy (SMA) plates has been proposed to realize resilient performance under low-to-medium seismic actions. In this conference paper, the detailed 3D numerical technique calibrated by the previous paper is adopted to examine the hysteretic behavior of the novel connection. A parametric study covering a reasonable range of parameters including the thickness of the SMA plate, friction coefficient between SMA plate and beam flange and pre-load of the bolt was carried out and the influence of the parameters was characterized. In addition, the effect of the SMA Belleville washer on the connection performance was also studied. The results of the numerical study showed that the initial connection stiffness and the energy-dissipation capacity of the novel connection can be enhanced with the increase of the thickness of the SMA plate. In addition, the initial connection stiffness and energy-dissipation behavior of the novel connection can be improved by increasing the friction coefficient or pre-load of bolts, whereas the increased friction level could compromise the self-centering behavior of the connection. The hysteretic curves of the numerical models of the connection also implied that the SMA washers may contribute to optimizing the connection behavior by increasing the connection stiffness and energy-dissipation capacity without sacrificing the self-centering behavior.

The Relationships Between Data, Information and Knowledge Based on a Preliminary Study of Engineering Designers

1999 ◽  
Author(s):  
Saeema Ahmed ◽  
Luciënne Blessing ◽  
Ken Wallace
Keyword(s):  
Aerospace Industry ◽  
Initial Study ◽  
Knowledge Based ◽  
Different Types ◽  
Preliminary Study ◽  
Initial Results

Abstract The aerospace industry, along with other industries, has acknowledged the need to bridge the experience gap between novice and experienced designers [Moore, 1997]. The research aims to identify the support a novice designer requires to gain experience faster. The focus of this paper is to present some initial results of a study of novice and experienced designers. This initial study highlighted the difficulty in establishing consistent and precise usage for the terms data, information and knowledge. It is concluded that data, information and knowledge are relative concepts that cannot be defined in absolute terms. As relative concepts, these help differentiate experts and novices, and different types of novices. The relationships between data, information and knowledge are examined with the aim of prompting a discussion.

scholarly journals Static and Fatigue Tests on Cementitious Cantilever Beams Using Nanoindenter

Micromachines ◽  
2018 ◽  
Vol 9 (12) ◽  
pp. 630 ◽  
Author(s):  
Yidong Gan ◽  
Hongzhi Zhang ◽  
Branko Šavija ◽  
Erik Schlangen ◽  
Klaas van Breugel
Keyword(s):  
Cement Paste ◽  
Fracture Behaviour ◽  
Test Procedure ◽  
Fatigue Behaviour ◽  
Fatigue Tests ◽  
Cantilever Beams ◽  
Fundamental Properties ◽  
Micromechanical Properties ◽  
Preliminary Study ◽  
Binding Component

Cement paste is the main binding component in concrete and thus its fundamental properties are of great significance for understanding the fracture behaviour as well as the ageing process of concrete. One major aim of this paper is to characterize the micromechanical properties of cement paste with the aid of a nanoindenter. Besides, this paper also presents a preliminary study on the fatigue behaviour of cement paste at the micrometer level. Miniaturized cantilever beams made of cement paste with different water/cement ratios were statically and cyclically loaded. The micromechanical properties of cement paste were determined based on the measured load-displacement curves. The evolution of fatigue damage was evaluated in terms of the residual displacement, strength, and elastic modulus. The results show that the developed test procedure in this work is able to produce reliable micromechanical properties of cement paste. In addition, little damage was observed in the cantilever beams under the applied stress level of 50% to 70% for 1000 loading cycles. This work may shed some light on studying the fatigue behaviour of concrete in a multiscale manner.

scholarly journals Modeling Wear for Heterogeneous Bi-Phasic Materials Using Discrete Elements Approach

2014 ◽  
Vol 136 (2) ◽  
Author(s):  
Matthieu Champagne ◽  
Mathieu Renouf ◽  
Yves Berthier
Keyword(s):  
Friction And Wear ◽  
Numerical Models ◽  
Real Life ◽  
Limited Range ◽  
Friction Material ◽  
Contact Interface ◽  
Discrete Elements ◽  
Proper Understanding ◽  
Scale Models ◽  
Automotive Brake

A proper understanding of the processes of friction and wear can only be reached through a detailed study of the contact interface. Empirical laws, such as Archard's, are often used in numerical models. They give good results over a limited range of conditions when their coefficients are correctly set, but they cannot be predicted: any significant change of conditions requires a new set of experimental coefficients. In this paper, a new method, the use of discrete element models (DEMs), is proposed in order to tend to predictable models. As an example, a generic biphasic friction material is modeled, of the type used in aeronautical or automotive brake systems. Micro-scale models are built in order to study material damage and wear under tribological stress. The models show what could be achieved by these numerical methods in tribological studies and how they can reproduce the behavior and mechanisms seen with real-life friction materials without any empirical law or parameter.

Initial results from International Thwaites Glacier Collaboration cruise NBP20-02

2020 ◽  
Author(s):  
Robert Larter ◽  
Julia Wellner ◽  
Alastair Graham ◽  
Claus-Dieter Hillenbrand ◽  
Kelly Hogan ◽  
...  
Keyword(s):  
Sea Level ◽  
Numerical Models ◽  
Sediment Cores ◽  
Hot Water ◽  
Seismic Profiles ◽  
Ice Shelf ◽  
Regional Survey ◽  
Amundsen Sea ◽  
Marine Research ◽  
Initial Results

<p>Thwaites Glacier (TG) is more vulnerable to unstable retreat than any other part of the West Antarctic Ice Sheet. This is due to its upstream-dipping bed, the absence of a large ice shelf buttressing its flow and the deep bathymetric troughs that route relatively warm Circumpolar Deep Water (CDW) to its margin. Over the past 30 years the mass balance of TG has become increasingly negative, suggesting that unstable retreat may have already begun. The International Thwaites Glacier Collaboration (ITGC) is an initiative jointly funded by the US National Science Foundation and the Natural Environment Research Council in the UK to improve knowledge of the boundary conditions and drivers of change at TG in order improve projections of its future contribution to sea level. The ITGC is funding a range of projects that are conducting on-ice and marine research, and applying numerical models to utilize results in order to predict how the glacier will change and contribute to sea level over coming decades to centuries.</p><p>RV Nathaniel B Palmer cruise NBP20-02, taking place from January­ to March 2020, will be the second ITGC multi-disciplinary research cruise, building on results from NBP19-02, which took place last year. Thwaites Offshore Research Project (THOR) aims during NBP20-02 include: extending the bathymetric survey in front of TG, collecting sediment cores at sites selected from the survey data, and acquiring high-resolution seismic profiles to determine the properties of the former bed of TG that is now exposed. The detailed bathymetric data will reveal the dimensions and routing of troughs that conduct CDW to the glacier front and will image seabed landforms that provide information about past ice flow and processes at the bed when TG was more extensive. The sediment cores, together with ones collected recently beneath the ice shelf via hot-water drilled holes, will be analysed to establish a history of TG retreat, subglacial meltwater release, and CDW incursions extending back over decades, centuries and millennia before the short instrumental record. Thwaites-Amundsen Regional Survey and Network Project (TARSAN) researchers will reach islands and ice floes via zodiac boats to attach satellite data relay loggers to Elephant and Weddell seals. The loggers record ocean temperature and salinity during the seals’ dives, greatly increasing the spatial extent and time span of oceanographic observations. In addition to work that is part of the THOR and TARSAN projects, another cruise objective is to recover and redeploy long-term oceanographic moorings in the Amundsen Sea. We will present initial results from NBP20-02.</p>

scholarly journals Using Recommender Systems for Matching Students with Suitable Specialization: An Exploratory Study at King Abdulaziz University

2021 ◽  
Vol 16 (03) ◽  
pp. 316
Author(s):  
Khloud Alshaikh ◽  
Naela Bahurmuz ◽  
Ola Torabah ◽  
Sara Alzahrani ◽  
Zainab Alshingiti ◽  
...  
Keyword(s):  
High School Graduates ◽  
Selection Process ◽  
Accuracy Ratio ◽  
King Abdulaziz University ◽  
Filtering Technique ◽  
Preliminary Study ◽  
And Performance ◽  
Preparatory Year ◽  
Initial Results ◽  
Selection Of

In Saudi Arabia, all high school graduates who want join local universities have to go through a preparatory year before selecting their specific specialization/major. One of the most concerning issues for those fresh undergraduate college students is the selection of their specialization. College specialization selection is critical for them, as their academic and career future will be affected by this decision. An un-suitable specialization selection will have unfortunate consequences, not only on the students' future but also on the university’s resources and budget. This paper sug-gests a solution to this problem by introducing a preliminary study of a recommend-er system (RS), which will recommend the appropriate specialization for the students based on various tests and grades during the preparatory year at King Abdulaziz University (KAU). The proposed system guides students through their specialization selection process based on their abilities. The collaborative filtering technique was used to build the RS and K-fold cross-validation was adopted to evaluate its accura-cy and performance. The results showed the prediction of a specialization for each student with good accuracy ratio. These promising initial results provide a feasible solution to assess this issue further in future studies.

scholarly journals The effect of salt in dilatant faults on rates and magnitudes of induced seismicity – first results building on the geological setting of the Groningen Rotliegend reservoirs

2017 ◽  
Vol 96 (5) ◽  
pp. s87-s104 ◽  
Author(s):  
Michael Kettermann ◽  
Steffen Abe ◽  
Alexander F. Raith ◽  
Jan de Jager ◽  
Janos L. Urai
Keyword(s):  
Rock Salt ◽  
Induced Seismicity ◽  
Loading Rate ◽  
Numerical Models ◽  
Fault Zones ◽  
Shear Loading ◽  
Ductile Material ◽  
Seismic Events ◽  
Fault Mechanics ◽  
Stick Slip

AbstractThe presence of salt in dilatant normal faults may have a strong influence on fault mechanics in the Groningen field and on the related induced seismicity. At present, little is known of the structure of these fault zones. This study starts with the geological evolution of the Groningen area, where, during tectonic faulting, rock salt may have migrated downwards into dilatant faults. These fault zones therefore may contain inclusions of rock salt. Because of its rate-dependent mechanical properties, the presence of salt in a fault may introduce a loading-rate dependency into fault movement and affect the distribution of magnitudes of seismic events. We present a first-look study showing how these processes can be investigated using a combination of analogue and numerical modelling. Full scaling of the models and quantification of implications for induced seismicity in Groningen require further, more detailed studies: an understanding of fault zone structure in the Groningen field is required for improved predictions of induced seismicity. The analogue experiments are based on a simplified stratigraphy of the Groningen area, where it is generally thought that most of the Rotliegend faulting has taken place in the Jurassic, after deposition of the Zechstein. This suggests that, at the time of faulting, the sulphates were already transformed into brittle anhydrite. If these layers were sufficiently brittle to fault in a dilatant fashion, rock salt was able to flow downwards into the dilatant fractures. To test this hypothesis, we use sandbox experiments where we combine cohesive powder as analogue for brittle anhydrites and carbonates with viscous salt analogues to explore the developing fault geometry and the resulting distribution of salt in the faults. Using the observations from analogue models as input, numerical models investigate the stick-slip behaviour of fault zones containing ductile material qualitatively with the discrete element method (DEM). Results show that the DEM approach is suitable for modelling the seismicity of faults containing salt. The stick-slip motion of the fault becomes dependent on shear loading rate with a modification of the frequency–magnitude distribution of the generated seismic events.

scholarly journals Experimental Study of Load-Bearing Cold-Formed Steel Walls Exposed to Realistic Design Fires

2014 ◽  
Vol 5 (4) ◽  
pp. 291-330 ◽  
Author(s):  
Anthony Ariyanayagam ◽  
Mahen Mahendran
Keyword(s):  
Failure Modes ◽  
Parametric Design ◽  
Numerical Models ◽  
Test Procedure ◽  
Natural Fire ◽  
Deformation Curves ◽  
Design Fire ◽  
Wall Panels ◽  
Measured Time ◽  
Set Up

This paper presents the details of full scale fire tests of LSF wall panels conducted using realistic fire time-temperature curves. Tests included eight LSF wall specimens of various configurations exposed to both parametric design and natural fire curves. Details of the fire test set-up, test procedure and the results including the measured time-temperature and deformation curves of LSF wall panels are presented along with wall stud failure modes and times. This paper also compares the structural and thermal behavioural characteristics of LSF wall studs with those based on the standard time-temperature curve. Finally, the stud failure times and temperatures are summarized for both standard and realistic design fire curves. This study provides the necessary test data to validate the numerical models of LSF wall panels and to undertake a detailed study into the structural and thermal performance of LSF wall panels exposed to realistic design fire curves.

Sign in / Sign up

Export Citation Format

Share Document