Combination Of Experimental Tests Research Articles

Prediction of compressive strength of the masonry of Al-Malwiya historic minaret in Samarra

Abstract This paper is motivated by the need for studies relevant to the strength of the construction of Al-Malwiya historic minaret in Samarra. A combination of experimental tests and an empirical formula is used to present the first approach for predicting the compressive strength of the masonry of Al-Malwiya. The experimental tests are conducted by testing samples of the historic clay bricks to evaluate the compressive strength of the masonry units. A number of empirical models are investigated to choose the most compatible model since there was inability to perform tests for the ancient gypsum mortar of the minaret. The empirical formula presented by Australian standard is found to be the most suitable formula for this study because it takes into consideration multiple parameters, in addition to its applicability for the low strength mortars as the ancient gypsum mortar in the minaret. A conservative value of 4.1 MPa is adopted in present study to predict the compressive strength of the masonry of Al-Malwiya.

Behavior of polyethylene under different triaxial stress states: An experimental and numerical study

The behavior of a semi-crystalline polymer under different triaxial stress states is studied through the combination of experimental testing and finite element simulation. Polyethylene round bar specimens with four different notch radii were stretched at crosshead speed of 1 mm/min until fracture. The continuum damage mechanics damage model and Gurson–Tvergaard–Needleman damage model were proposed and applied to the finite element simulation. The results of engineering stress–displacement curves determined from finite element simulation match experimental results. Finite element simulation without considering damage and with the consideration of damage was conducted to determine the damaged and undamaged true stress–strain relationship of polyethylene materials, respectively. Damage evolution model was established based on the degradation of true stress. The finite element model was further applied to study the distribution of stress triaxiality for specimens with different notch radii and the effect of stress triaxiality on damage evolution, critical damage parameters, and fracture strain. The results show that the distribution of the stress triaxiality on the cross section of the specimen is not uniform, and as the stress triaxiality increases, the position where the maximum stress triaxiality occurs moves from the center point to two-third the radius from the center. Furthermore, the damaged true stress and the undamaged true stress increases with the decrease of the stress triaxiality when the strain is below 0.3, but decreases with the increase of stress triaxiality when the strain is larger than 0.3. In addition, it was found that the greater the stress triaxiality, the earlier the onset of damage and the faster the evolution, but the smaller the fracture strain.

Effect of stress triaxiality on the damage of polyethylene

In this study, the effect of the triaxial stress state on the stress/strain behavior and damage of polyethylene (PE) was investigated through a combination of experimental testing and finite-element (FE) simulation. Notched round bars with four different notch radii (0.5, 2, 5, and 20 mm) were stretched at a crosshead speed of 1mm/min until fracture. A phenomenological constitutive model was proposed to describe the mechanical behavior of PE specimens with different radii. Parameters of the constitutive model were adjusted until the curve of engineering stress-displacement from the FE simulation matched the experimental results. The FE model was further applied to obtain the data on stress triaxiality and true stress-strain curves of PE specimens. The results show that stress triaxiality and yield stress increase with the reduction of notch radii. However, the true stress decreases when the notch radii are reduced, suggesting that higher triaxiality aggravates the damage accumulation.

Cold-formed steel channel sections under end-two-flange loading condition: Design for edge-stiffened holes, unstiffened holes and plain webs

Abstract In cold-formed steel (CFS) channel sections, web holes are becoming increasingly popular. Such holes, however, result in the sections becoming more susceptible to web crippling, especially under concentrated loads applied near the web holes. Traditional web holes are normally punched or bored and are unstiffened. Recently, a new generation of CFS channel sections with edge-stiffened web holes has been developed by the CFS industry and is being widely used. However, no research is available in the literature which investigated the web crippling strength of CFS channel sections with edge-stiffened circular web holes under the end-two-flange (ETF) loading conditions. A combination of experimental tests and non-linear FEA were used to investigate the effect of such stiffened holes on web crippling behaviour under ETF loading conditions. The results of 30 web crippling tests are presented. Non-linear FE models are described, and the results are compared against the laboratory test results; a good agreement was obtained in terms of both the strength and failure modes. The results indicate that the stiffened holes can significantly improve the web crippling strength of CFS channel sections. A parametric study involving 1116 FEA was then performed, covering the effect of different hole sizes, edge-stiffener lengths and fillet radii, length of the bearing plates and position of holes in the web. Finally, design recommendations in the form of web crippling strength reduction factors are proposed, that are conservative to both the experimental and FE results.

Estimation of the Normal Contact Stiffness for Frictional Interface in Sticking and Sliding Conditions

Modeling of frictional contact systems with high accuracy needs the knowledge of several contact parameters, which are mainly related to the local phenomena at the contact interfaces and affect the complex dynamics of mechanical systems in a prominent way. This work presents a newer approach for identifying reliable values of the normal contact stiffness between surfaces in contact, in both sliding and sticking conditions. The combination of experimental tests, on a dedicated set-up, with finite element modeling, allowed for an indirect determination of the normal contact stiffness. The stiffness was found to increase with increasing contact pressure and decreasing roughness, while the evolution of surface topography and third-body rheology affected the contact stiffness when sliding.

Prediction of flow induced vibration of a flat plate located after a bluff wall mounted obstacle

Accurate prediction of Flow Induced Vibration phenomena is currently a field of major interest due to the use of lightweight materials in the automotive and aerospace industry. This article studies the turbulent flow around a wall-mounted obstacle, and the induced deformations produced by the pressure fluctuations on a plate located downstream the obstacle. The methodology used is a combination of experimental tests and numerical simulations. On one side, experiments were carried out in a wind tunnel test facility equipped with Particle Image Velocimetry to characterize the fluid velocity field, and laser vibro-meter to measure the vibrations of the plate. On the other side, Fluid-Structure Interaction (FSI-one-way) has been calculated by considering different turbulence modeling approximations (RANS and LES). Finally, numerical results have been analyzed and validated against the experiments in terms of main flow structures and the vibroacoustic response of the plate.

Failure and energy absorption characteristics of four lattice structures under dynamic loading

Two novel diamond lattice structures (Dfcc and Dhex) and the typical face-centered cubic (FCC) and body-centered cubic (BCC) lattice structures are manufactured by selective laser melting (SLM), and the effects of cell topology and relative density on the dynamic behavior of these structures are studied through a combination of experimental tests and numerical simulation. It is observed that in Dfcc and Dhex, failure initiates at the connection points between rods in the middle of the structure, causing a sudden drop of the measured stress value. However in FCC and BCC, failure initiates in the face-truss junction. Generally, the FCC and BCC are dominated by stretching and bending of the rods respectively, whereas the Dfcc and Dhex are a mixture of the two deformation modes. The results show that the mechanical properties of the lattice structures with different relative density can be described by a power law function. Moreover, for the lattice structures with the same rod diameter of 0.8 mm, FCC out-performs other structures in terms of specific strength, specific modulus and energy absorption. This gives evidence that lattice structures with the stretching-dominated deformation mode are more likely to exhibit better mechanical properties under dynamic loading.

Fuel – clad chemical interaction evaluation of the TREAT reactor conceptual low-enriched-uranium fuel element

The Transient Reactor Test (TREAT) facility resides at the Materials and Fuels Complex (MFC) at Idaho National Laboratory (INL). The TREAT reactor is currently undergoing design and engineering studies for its conversion from a high enriched uranium (HEU) to a low-enriched uranium (LEU) core. The conceptual design of the LEU fuel element identified two main design differences compared with the HEU fuel element; namely, it will contain four times more fissionable material in its graphite matrix and distinct nuclear-grade Zirconium alloy, as Zircaloy-3 was used in the HEU fuel assembly and is not commercially available currently. These design changes may impact the magnitude of chemical interaction between fuel and cladding materials during physical contact under expected TREAT operation conditions and, therefore, was evaluated through a combination of experimental testing and thermodynamic modeling in order to determine implications for the fuel assembly. In this study, two potential cladding material types, Zircaloy-4 or Zr-1Nb alloys, were evaluated, and it was found for both material types that the extent of interaction and specific chemical reactions are minimal and no detrimental effect on the overall cladding properties is observed. The resulting interaction layer of 3–6 μm was measured after a 2-week exposure at 820 °C. The thermodynamic analysis was extended to temperatures beyond the TREAT reactor operation and accident conditions in order to give some insight that may be of interest for other reactor systems as the High Temperature Gas Reactors (operation above 1000 °C) and for Nuclear Reactor Severe Accident phenomenology study where the UO2 fuel could reach temperatures over 2800 °C and melt.

Improving the adsorption of oily collector on the surface of low-rank coal during flotation using a cationic surfactant: An experimental and molecular dynamics simulation study

The effect of a cationic surfactant, dodecyltrimethylammonium bromide (DTAB), on low-rank coal flotation using an oily collector (dodecane) was investigated by a combination of experimental tests and molecular dynamics simulations. Flotation results showed that the addition of DTAB during pulp conditioning increased the clean coal yield, while a high concentration of DTAB exerted a negative influence. To explain the flotation behavior and analyze the interaction between low-rank coal, DTAB and dodecane, a series of experimental tests were conducted and the results indicated that a relatively lower concentration of DTAB is beneficial for the adsorption of dodecane on low-rank coal surface. In addition, by measuring the induction time, it was found that low-rank coal particles were easily adhered to bubbles in the presence of suitable concentration of DTAB. However, a high concentration of DTAB brings about an adverse effect. Later, molecular dynamics (MD) simulations were carried out to illustrate the positive effect of DTAB on the adsorption reaction between low-rank coal and dodecane. The results showed that the abundant number of oxygen-containing groups in low-rank coal are responsible for the limited adsorption of nonpolar dodecane molecules on its surface, while the pre-adsorption of DTAB on the surface of low-rank coal enhances dodecane adsorption. This can be ascribed to the exposed hydrophobic structure of the coal-DTAB complex. As a result, dodecane molecules were more easily adsorbed on the surface of low-rank coal and the attraction of low-rank coal to dodecane in the presence of DTAB resulted in a lower mobility of dodecane molecules, and a larger interaction energy between dodecane and low-rank coal. The simulation results are in good agreement with experimental results.

Loss Analysis and Efficiency Improvement of an Axial-Flux PM Amorphous Magnetic Material Machine

This paper presents research work on a 12-slot ten-pole tapered axial-flux permanent-magnet machine utilizing amorphous magnetic material in the stator core. Novel loss separation techniques are described, including mechanical loss and locked-rotor tests. Mechanical loss estimation is based on a combination of experimental tests and 3-D finite-element model analysis using an uncut stator. The locked-rotor test is introduced to separate the stator and rotor losses by eliminating the uncertainty associated with mechanical loss. High rotor yoke losses were identified in the baseline design. The rotor design was modified and a significant improvement in efficiency was demonstrated.

3D numerical modelling and experimental validation of an asphalt solar collector

Research about renewable technologies for thermal energy collection is crucial when critical problems such as climate change, global warming or environmental pollution are concerned. Transforming solar energy into thermal energy by means of asphalt solar collectors might help to reduce greenhouse gas emissions and fossil fuel consumption. In this paper, a laboratory-scale asphalt solar collector formed by different slabs has been characterized by applying numerical techniques. An experimental test where the thermal performance of the collector was determined for three values of heat exchange fluid flow rate was carried out for the validation of the numerical model. Then, the CFD model was used to analyse the thermal response of the collector according to the following parameters: flow rate, solar irradiance, size and thickness. Results show that increasing values of heat exchange fluid flow rate result in better thermal performances. Likewise, increasing values of irradiance and size of the collector lead to higher values of thermal performance, although other parameters should also be considered for the final design of the system. Finally, under the conditions here considered, the thickness of the collector turned out not to be as significant as expected in relation to its thermal response. The combination of experimental tests and CFD codes can be considered a powerful tool for the characterization of asphalt solar collectors without incurring significant costs related to experimental field tests.

Momentum transfer during the impact of granular matter with inclined sliding surfaces

Increasing the inclination of a rigid surface that is impacted by a collimated granular flow reduces the fraction of granular matter momentum transferred to the surface. Recent studies have shown that the momentum reduction depends upon a frictional interaction between the granular flow and the impacted surface. High coefficient of friction surfaces suffer significantly more momentum transfer than predicted by resolution of the incident momentum onto the inclined plane. This discovery has raised the possibility that inclined surfaces with very low friction coefficients might reduce the impulsive transferred by the impact of high velocity granular matter. Here the use of a lubricated sliding plate is investigated as a means for reducing interfacial friction and impulse transfer to an inclined surface. The study uses a combination of experimental testing and particle-based simulations to investigate impulse transfer to rigid aluminum surfaces inclined either perpendicular or at 53° to synthetic sand that was impulsively accelerated to a velocity of 350–500m/s. The study shows that impact of this sand with lubricated plates attached to an inclined surface rapidly accelerates them to a velocity of about 55–70m/s, and reduces the impulse transferred to the inclined surface below. The reduction of impulse by this approach is comparable to that achieved by changing the inclination of the surface.

Assessment of thermal performance of gypsum-based composites with revalorized graphite filler

European standards place great emphasis on the reintroduction of waste in the production chain. In this research, a combination of experimental tests has been carried out to analyse the use of revalorized isostatic graphite powder waste in gypsum-based boards. A series of gypsum pastes was prepared with a graphite content ranging from 0% to 25%, by weight substitution, and two w/b ratios. Its addition significantly increased the bulk density, thermal conductivity and emissivity of the samples until 19%, 97% and 10%, respectively. Additionally, a reduction of 54% in thermal fluxes towards the outside can be achieved when graphite-gypsum boards replaced gypsum ones at radiative constructive solutions.

A finite-element-based approach to characterising FTire model for extended range of operation conditions

ABSTRACTIn order to accurately predict vehicle dynamic responses when traversing high obstacles or large bumps, appropriate tyre models need to be developed and characterised. Tyre models used in vehicle ride and durability are usually characterised by experimental tests on the tyre. However, limitations in rig design and operating conditions restrict the range of test conditions under which the tyre can be tested, hence characterisation of the tyre behaviour during extreme manoeuvres may not be possible using physical tests. In this study, a combination of experimental tests and finite-element (FE) modelling is used in deriving Flexible Ring Tire (FTire) Models appropriate for different levels of tyre/road interaction severity. It is shown that FE modelling can be used to accurately characterise the behaviour of a tyre where limitations in experimental facilities prevent tyre characterisation using the required level of input severity in physical tests. Multi-body simulation is used to demonstrate that the FTire model derived using extended range of obstacles produces more accurate transient dynamic response when traversing low and high road obstacles.

Hierarchical Graphene‐Based Films with Dynamic Self‐Stiffening for Biomimetic Artificial Muscle

Biological tissues such as muscle cells can adapt their structural and mechanical response upon external mechanical stimuli. Conversely, artificial muscles, intended to reproduce the salient functional features of biological muscles, usually undergo mechanical fatigue when subjected to dynamic stress. Besides passively improving the resilience to dynamic loads, here, it is reported that macroscopic films based on graphene and its chemical derivate exhibit an increase in modulus by up to 84% after subjected to a low‐amplitude (0.1%) dynamic tension. Through a combination of experimental testing and molecular dynamics simulations, the unique self‐stiffening behavior is attributed to the straightening and reorientation of graphene sheets and is further tuned through tailoring interlayer adhesion. Meanwhile, artificial muscles based on graphene films are designed and interestingly improved stiffness of our muscle materials after “training” are demonstrated. These results help to harness the stiffening mechanism and can be useful for the development of adaptable structural materials for biomechanical applications.

Finite element modelling of the low velocity impact response of composite plates with block copolymer nano-reinforcements

The use of composite materials in passive safety structures has increased significantly due to their low specific mass and high energy absorption capacities. The purpose of this study is to develop and validate a macroscopic numerical model to simulate the impact response of composite laminates with nano-reinforcements. The impact resistance of laminate with Kevlar fibre reinforced epoxy resin embedded with Nanostrength®, an acrylate triblock copolymer that self-assembles in the nanometer scale is investigated. Low velocity impact experiments were performed on square plates clamped by means of a circular fixture using an instrumented drop tower. Images of the composite laminate during impact were recorded by a high-speed video camera fixed underneath the plate. An approach for modelling these composites in the commercial finite element code LS-Dyna using constitutive model based on the theory of continuum damage mechanics developed by Matzenmiller, Lubliner and Taylor - called MLT model - is presented. LAMINATED COMPOSITE FABRIC material model, available in the LS-Dyna material model library as (MAT58), was chosen for modelling the low velocity impact of the Kevlar composite plate. The model requires input of material properties in shear, tension, and compression to define stress-strain behaviour within the laminate. The parameters needed for the model are determined using a combination of experimental tests and parametric analysis. The macroscopic response of the Kevlar composite with and without nanoparticles in the resin subjected to impact loading are simulated in LS-Dyna with the phenomenological material model, and is validated by comparison with experiments. It was found that the Kevlar epoxy composite material with Nanostrength M52N had better resistance to perforation compared to the lamiante with neat resin.

Failure and energy absorption characteristics of advanced 3D truss core structures

Lightweight core structures with high strength and high potential for energy absorption are crucial for a range of applications in the aerospace and automotive industry, but data is lacking for validated failure prediction. We undertake both compression and shear tests to determine and successfully predict the energy absorption capacity of Ti-based Kagome and atomic lattice truss configurations (bcc, f2cc and f2bcc) built by selective laser melting. The failure characteristics are determined through a combination of experimental tests and numerical finite element simulations. The novel failure prediction approach for truss structures utilises a ductile metallic damage model with triaxial stress state dependence and results in very good agreement of deformation patterns, predicted failure strain and failure location. These findings result in the development of optimum design strategies for truss-based structures. The four unit cell structures are ranked against traditional core structures with the help of comprehensive Ashby design charts for both strength and energy absorption. Of the four lattice types investigated, Kagome structures perform best and also show superior strength compared to traditional core materials for the same density, while their energy absorption capacity is competitive with titanium and aluminium honeycomb materials.

Ballistic damage in hybrid composite laminates

Ballistic damage of hybrid woven-fabric composites made of plain-weave E-glass- fabric/epoxy and 8H satin-weave T300 carbon-fabric/epoxy is studied using a combination of experimental tests, microstructural studies and finite-element (FE) analysis. Ballistic tests were conducted with a single-stage gas gun. Fibre damage and delamination were observed to be dominating failure modes. A ply-level FE model was developed, with a fabric-reinforced ply modelled as a homogeneous orthotropic material with capacity to sustain progressive stiffness degradation due to fibre/matrix cracking, fibre breaking and plastic deformation under shear loading. Simulated damage patterns on the front and back faces of fabric-reinforced composite plates provided an insight into their damage mechanisms under ballistic loading.

Titanium based cranial reconstruction using incremental sheet forming

In this paper, we report recent work in cranial plate manufacturing using incremental sheet forming (ISF) process. With a typical cranial shape, the ISF process was used to manufacture the titanium cranial shape by using different ISF tooling solutions with and without backing plates. Detailed evaluation of the ISF process including material deformation and thinning, geometric accuracy and surface finish was conducted by using a combination of experimental testing and Finite Element (FE) simulation. The results show that satisfactory cranial shape can be achieved with sufficient accuracy and surface finish by using a feature based tool path generation method and new ISF tooling design. The results also demonstrate that the ISF based cranial reconstruction has the potential to achieve considerable lead time reduction as compared to conventional methods for cranial plate manufacturing. This outcome indicates that there is a potential for the ISF process to achieve technological advances and economic benefits as well as improvement to quality of life.

Effects of adherend thickness and taper on adhesive bond strength measured by portable pull-off tests

Portable pull-off test using the Pneumatic Adhesion Tensile Testing Instrument (PATTI) has been employed to quantify the residual strength of bonded patch repairs on retired aircraft, with a view towards establishing a reliability-based airworthiness certification methodology for bonded repairs of primary structures. The pull-off strength obtained using this field-testing method may be affected by two major factors: the structure's cross-sectional thickness and tapering near repair edges. This paper aims to investigate and quantify the effects of these two parameters on the pull-off strength, through a combination of experimental testing and computational modelling. By subjecting scarf joints of varying angles to tensile loading, film adhesive FM300 was found to obey the modified Drücker–Prager/cap plasticity criterion. With these data as inputs to a finite element model and a failure criterion that defines final fracture as when the maximum strain at a characteristic distance reaches the adhesive's failure strain, strength predictions of PATTI tests were carried out, with results being compared to experimental data. The results show that the modified Drücker–Prager/cap plasticity model gives better prediction than the von Mises yield criterion, with the characteristic distance being determined by an inverse method using test results pertinent to tensile butt joints.