An experimental and numerical investigation on tyre impact

A key issue in the design of tyres is their capability to sustain intense impact loads. Hence, the development of a reliable experimental data basis is important, against which numerical models can be compared. Experimental data on tyre impact in the open literature is somewhat rare. In this article, a specially design rig was developed for tyre impact tests. It holds the test piece in a given position, allowing a drop mass with a round indenter to hit pressurised tyres with different impact energies. A high-speed camera and a laser velocimeter were used to track the impact event. From the laser measurement it was possible to obtain the impact force and the local indentation. A finite element study was then conducted using material properties from the open literature. By comparing the experimental measurements with the numerical results, it became evident that the model was capable of predicting the major features of the impact of a mass on a tyre. This model is therefore of value for the assessment of the performance of a tyre in extreme cases of mass impact.     

An experimental investigation of an ejector for validating numerical simulations

Supersonic ejectors have been used in cooling/refrigeration applications since the early 1900s. Interest in supersonic ejectors has been rekindled by recent efforts to reduce energy consumption; ejector refrigeration systems can be powered by solar energy or by waste heat generated by another process. This paper describes an experimental test bench using R245fa that was assembled and operated at CanmetENERGY in Varennes. The results from this test bench provide a source of reference data that may be used to validate numerical models of ejectors that could be used in refrigeration applications. Limited results from two numerical models are presented for comparison; global results from a 1D model and results from a detailed CFD model that show the flow field inside the ejector.     

An experimental and numerical investigation into the damage mechanisms in notched composites

Investigations of the effect of size on the tensile strength of composite laminates containing circular holes show that there is a large difference both in failure stress and mechanism due to changes in test configuration. This is particularly true of the ply and laminate thickness, and hole diameter. Interrupted tests have been performed on open hole tensile specimens at different load levels to determine the progressive damage development, evaluated through non-destructive testing (X-ray and C-scanning). The tests were also analysed using a novel Finite Element Modelling technique. This was able to accurately predict the wide range of ultimate strengths measured with variation in test parameters, principally through incorporation of the sub-critical damage in the analysis. A significant damage mechanism was seen to be delamination at the hole edge which generally occurred at a lower stress for a smaller hole diameter to ply block thickness ratio. Delaminations allowed damage to join up through the thickness of the laminate and propagate. In ply-level scaled specimens, the delamination propagation was the ultimate failure mode of most of the specimens. In sub-laminate level scaled specimens, localised damage relieved stress in the 0° fibres at the hole edge, delaying the onset of fibre failure. Less damage was seen for larger holes, thus leading to a decreasing failure stress with increasing hole diameter.     

压下率对轧制单层晶极薄带晶界滑移特性的影响

采用退火态单层晶轧制铜箔为原料,进行不同压下率的箔轧.以多晶体位错滑移及塑性流动机制为基础,建立了考虑潜在硬化和晶格转动效应的率相关晶体滑移本构模型,分析了压下率对轧制单层晶极薄带晶界附近区域变形分布特性、取向演化和滑移系激活规律的影响,并探讨其机理.确定了合理的材料本构参数,铜箔拉伸实验与晶体塑性有限元模拟得到的应力-应变曲线一致.所建立的晶体塑性有限元模型,可很好的模拟最大压下率达到80%时轧制单层晶铜箔的变形过程.结果表明:1)由于晶粒形状、晶界及晶粒取向的作用导致晶内-晶间变形分布非均匀性;2)由于晶粒间复杂的相互作用导致晶粒取向主要绕横向(TD)进行旋转,且旋转角度和取向分散度随压下率的增加而增大;3)在晶内-晶间不同区域的滑移系启动存在显著差异,启动滑移系随压下率的增加而增多,当压下率小于等于60%时,在晶粒表层和晶界处,滑移系成对发生启动,当压下率达到80%时,表层和晶界处为多滑移系启动情形;4)滑移最先从晶粒表层和晶界处开始,然后向晶粒内部延伸.     

Enhancing fine particle separation by hybrid-electrostatic-turbulence coagulation: An experimental and numerical investigation

The electrostatic precipitator(ESP) has low efficiency in removing sub-micron particles. Coagulation technology, as a fine particle pretreatment technology, uses an external effect to agglomerate and grow fine particles, increase the average particle size, and make it easier to remove by subsequent dust removal equipment. However, the coagulation efficiency of a single coagulation technology is limited. Aiming at the particle charging mechanism and coagulation mechanism in the electric/turbulent composite coagulation process of fine particles, this paper uses a combination of numerical simulation and experiment to study the effects of different structural parameters, discharge parameters and flue gas parameters on corona discharge and particle charge. On this basis, the coagulation characteristics of charged particles in the turbulent flow field are studied. The results show that, when the Angle between the tip of the arista electrode is 90°, the corona discharge effect is the best. With the increase of supply voltage and temperature, the charge of particles increases. When the applied positive voltage is 29 kV and negative voltage is ?35 kV, the total coagulation coalescence efficiency of fine particles reaches the maximum. The coagulation efficiency increases with the increase of temperature, but decreases with the increase of inlet flow rate.     

An experimental and numerical study on adhesive joints for composites

In many composites structures the use of joints allows not only more versatility during the assemblage process but also reduces the cost during the manufacturing. As joints are considered regions of weakness, their study has been conducted since late 1930s. Researchers have been working on new joint designs looking for better performances. One of these new designs is the bonded wavy-lap joint presented by Zeng and Sun in 2001. This paper addresses the advantages and disadvantages of the wavy-lap joint and a modified wavy-lap joint design is studied. To be able to guarantee the data consistency a statistical study is performed considering not only the sample size population but also the statistical differences between the single-lap and wavy-lap joints. Besides, the experimental tests, a finite element simulation is carried out to analyze the stress fields inside the joints. The results show an average increase on loading to failure close to 41%. This fact could be due to the compressive stress field developed inside the wavy-lap joint. In addition, this stress field distribution can also be the reason for the adherent delamination observed on the wavy-lap joints. So far, the modified wavy-lap joint seems to lead to stronger joints.     

A numerical and experimental investigation on the use of J-integral

Finite element analysis was used to determine numerically Rice's J-integral values in centrally notched plates of 4340 steel. These numerical values were compared with corresponding J-integral values using Dugdale model and antiplane strain model with a power law hardening of n = 0.3. J-integral was also computed for a crack extending into its own plastic yield region under constant loading. For increasing level of loading, σ, the rate of increase in J-integral decreases and J-integral remains almost constant at $\text{σ}\text{σ}{}_{\mathrm{YS}}\text{= 1}$ under such crack extension.A limited number of fracture tests were conducted with centrally notched 4340 steel specimens heat treated to yield strength levels of 150,180, 210 and 240 ksi. Fracture data showed that the critical J-integral, calculated and measured, is insensitive to crack tip sharpness for the lower strength 4340 material and thus the J_c fracture criteria appears suited in correlating fracture data.     

Experimental investigation on thermal wear of high speed steel rolls in hot strip rolling

Abstract

The thermal wear ratio of a high speed steel roll was investigated experimentally in hot strip rolling with a DTW- 166 thermal wear testing machine developed by the authors. It is clear that the wear ratio increased with number of cycles. Some of the increase in wear was because of the black oxide layer generated on the roll surface at the beginning. The wear ratio also increased as slippage ratio and loads increased. Loads played a more important role than slippage ratio for thermal wear. The appearance of the roll surface was observed by SEM under different conditions. The mechanism of thermal wear was composed of adhesive, microploughing, microcutting, oxidation, and plastic slippage wear.     

An experimental and numerical investigation on torsional strengthening of solid and box-section RC beams using CFRP laminates

The issue of maintenance and repair/upgrading of existing structures has become a major issue, particularly extending the service lifespan of bridges. Fibre reinforced polymer (FRP) has shown great promise as a state-of-the-art material in flexural and shear strengthening as external reinforcement. However, little attention has been paid to torsional strengthening in terms of both experimental and numerical research. This paper reports the experimental work in an overall investigation of torsional strengthening of solid and box-section reinforced concrete beams with externally-bonded CFRP. This was found to be a viable method of torsional strengthening. Numerical work was carried out using non-linear finite element (FE) modelling. Good agreement in terms of torque–twist behaviour, steel and CFRP reinforcement responses, and crack patterns was achieved. The unique failure modes of all the specimens were modelled correctly as well.     

An experimental and numerical investigation of the effect of macro-textured tool surfaces in hot stamping

This paper presents a method of increasing draw-ability of materials in hot stamping processes using forming tools with macro-scale textures on the tool surfaces. Firstly, a series of tool texture designs and orientations were presented and a test programme was designed for the experimental investigation. Top-hat shape drawing experiments in cold and hot stamping conditions were conducted to evaluate the effect of macro-scale tool surface textures on the material drawing. Texture directional and texture feature effects of the blankholders on the draw-ability of the material have been investigated. A finite element model of the top-hat drawing process with textured tool surfaces has been established and validated from experimental data. Further FE process modelling has been carried out and the effects of texture features and forming speed have been studied. The relationships between texture designs and material drawing results have been analysed. The developed FE model can provide a guide to design the geometry of tool textures and optimise the hot stamping process parameters.     

An experimental and numerical study on omega stringer debonding

Omega stringers offer interesting structural capabilities and are expected on future aircraft fuselages. In postbuckling mode, the final failure of these structures may occur by stringer debonding between stringer flanges and the skin of the fuselage. In this study, it is demonstrated that the use of fracture mechanics allows to predict skin/omega stringer separation under multiple load cases. Three different load cases and experiments are presented allowing a debonding to start at different locations: at free flange edges or at the inner radius of the omega. Firstly, a skin/stringer configuration subjected to three point bending following the longitudinal axis of the stringer was tested. For this configuration, a numerical study was made and shows the influence of a refined mesh taking into account resin fillets. Secondly, new specimens were obtained by cutting into slices the longitudinal specimen. Those specimens were subjected to four points bending. It has been shown that the upper rolls position of the test jig could modify the debonding location. Numerical models have allowed to determine accurately the debonding location and the associated load level. For some specimens, resin fillets were removed from the flange tips and their effect were assessed numerically and experimentally.     

Evolution of at-rest lateral stress for cemented sands: experimental and numerical investigation

We present measurements of the evolution of the at-rest lateral stress coefficient K ₀ for cemented sands in a modified oedometer and provide additional insights into material response using discrete element method (DEM) simulations. A new scheme for the measurement of K ₀ is adapted to obtain horizontal stress for the entire stress history with parallel measurement of shear wave velocity. Results show that the horizontal stress of uncemented sand linearly increases, while debonding in cemented sands is characterized by a non-linear evolution of horizontal stress. Cement content governs the stress regime in which decementation initiates. The at-rest lateral stress coefficient of cemented sands increases during decementation, resulting in higher values for overconsolidated specimens. The recovery of K ₀ values is manifested at the preconsolidation stress during reloading. Cemented sands collapse followed by decementation and subsequent changes in K ₀ values. The DEM simulations reasonably reproduce laboratory specimen-scale response and are used to highlight the evolution of particle contact force, gradual debonding of cement, and the formation of a blocky structure in cemented sands at the particle-scale. These observations are consistent with inferred response of physical specimens at the particle scale, yet this behavior is not directly observable in the laboratory, highlighting the particular effectiveness of an integrated physical-numerical investigation. The interparticle contact stiffness of cemented sands controls the evolution of horizontal stress at low vertical stress, and the decementation causes the convergence of K ₀ values towards those of uncemented sands at high vertical stress.     

超薄铜铝复合电缆带的制备及其力学性能研究

针对电缆带以铝节铜的市场需求和超薄铜铝复合板带制备技术缺乏的现状,提出了包含叠轧的多道次累积轧制复合工艺,同时采用快速在线退火工艺成功制备了厚度为0.12 mm的超薄铜铝复合电缆带,并对其不同道次和不同退火工艺下的拉伸力学性能进行了分析.研究表明:采用高温短时在线热处理可以达到低温长时退火处理的效果;超薄铜铝复合带的力学性能对厚度特别敏感;改变初始坯料状态和降低中间退火温度可以改善最终复合带的力学性能.     

An ALE hydrodynamic lubrication finite element method with application to strip rolling

A method that incorporates the hydrodynamic lubrication analysis into the arbitrary Lagrangian Eulerian (ALE) finite element analysis is developed for steady-state strip rolling simulation. By employing the ALE formulation, only part of the workpiece, which is subjected to large plastic deformation within the roll-bite region, is modelled, so that the computational cost is substantially reduced. In the hydrodynamic lubrication formulation, the effect of surface roughness on the lubricant flow is taken into consideration by the use of an average flow model. The friction stress is expressed in terms of forming variables such as surface roughness, lubricant and workpiece properties, film thickness, forming speed and process geometry. Furthermore, the elastic deformation of rolls is also analysed by the boundary element method to avoid the finite element discretization inside the rolls. Two numerical examples, aluminium and steel strip rolling processes, are presented to demonstrate the merits of the proposed method.     

Transverse impact of free–free square aluminum beams: An experimental–numerical investigation

A combined experimental–numerical analysis was performed to model transverse impact of free–free square aluminum beams loaded at different locations along their length. The applied impact load was obtained from tests carried out on a single Hopkinson pressure bar. The 3D elastic–plastic numerical simulations show that the plastic deformation, adjacent to the impact location, is due to combined dominant bending and stretching modes. Most of the plastic deformation is confined to the impact zone but some partial additional plastic hinges are observed to develop. The plastic strain magnitude and distribution near the impact zone are similar for all tested impact locations, but higher for the more symmetrical impacts. The conversion of impact energy into kinetic, elastic strain energy and plastic dissipation work is characterized for various impact locations along the beam. It is observed that symmetrical impact results in higher plastic dissipation and lower kinetic energy as opposed to unsymmetrical impact. Between 52% and 76% of the applied energy is converted into plastic dissipation energy.     

An experimental and numerical study of crack closure

Fatigue crack propagation and crack closure are studied in Al 2024-T3 under a wide range of ΔK. An elastic-plastic finite element procedure to analyze crack closure for growing cracks is presented. Numerical results are obtained for plane stress and plane strain conditions for different stress ratios. Measurements of opening loads compare well with numerical predictions within the Paris regime. Fractographic observations and compliance measurements indicate that oxide-induced and roughness-induced crack closure substantially increase the opening loads in the near-threshold regime.     

An experimental and numerical investigation of ductile crack growth characteristics in surface cracked specimens under combined loading

Fracture mechanics tests have been performed in the upper shelf region of a steel on large surface cracked plate (SCT) specimens and on small compact tension (CT) specimens. Some of the SCT specimens were subjected to combined tension and bending in such a way that the loading was strongly non-proportional. Crack growth characteristics were compared between the specimens in order to assess possible influences of geometry and nonproportional loading. The differences observed could unambiguously be reduced to and correlated with differences in constraint. Constraint parameters were evaluated by detailed three-dimensional finite element computations and quantities for growing cracks were interpreted on the basis of deformation theory considerations, in analogy with the commonly used J _R-philosophy. It was noted that the initiation of ductile crack growth along a three-dimensional crack front appears to be independent of the degree of local constraint. However, the increase in toughness for a growing crack was markedly affected by the degree of local constraint. Some estimates of the constraints effects regarding stability considerations were also made.     

On the experimental and numerical investigation of clay/epoxy nanocomposites

Due to increasing use of clay/epoxy nanocomposites in industry, investigation of mechanical properties of clay nanocomposites has become of great interest. While the stiffening mechanism of clay nanocomposites is well documented, there is still not a clear understanding about how addition of clays affect the fracture behavior of clay/epoxy nanocomposites. The main aim of this paper is to measure and explain the effect of clays on ductility reduction of these nanocomposites. First, epoxy and clay/epoxy nanocomposites with different clay weight ratio were built. Then, the damage parameters of epoxy and clay/epoxy nanocomposites were measured by variation of the elasticity modulus. Based on loading–unloading experiments, the Lemaitre damage parameters for epoxy and clay/epoxy nanocomposites were extracted. Crack initiation and propagation in dog-bone sample were simulated for epoxy and clay/epoxy nanocomposites using the eXtended Finite Element Method (XFEM). The comparison between experimental and numerical results shows that the proposed method can predict the crack initiation location and propagation path in clay/epoxy nanocomposites.     

An experimental investigation on flash butt welded rails

In this paper, experimental studies performed for flash butt welded rails used in Turkish railways network having 49E1 and 60E1 rail sections are presented. These studies comprise of full-scale laboratory tests such as four point bending fatigue and three-point slow bending tests, as well as related instrumentation of test specimens and data measurement. Fatigue and bending tests are prepared and carried out in accordance with EN 14587-2 standard. The fracture surfaces of the welded samples are examined to identify the associated failure modes. The fatigue test results are superimposed on a S–N diagram derived from earlier results reported as a part of the European Commission steel rails research project. A best fit curve following an exponential function is derived to describe the load deflection behavior of the weld under the slow bend testing conditions. It is shown that a single component of the equation defining the best fit curve is the factor controlling the scattering in the non-linear part of the load deflection curve, and hence control of this parameter can also be used to impart consistency to the welding process.