Comparison of Flow and Transport Experiments on 3D Printed Micromodels with Direct Numerical Simulations

Understanding pore-scale flow and transport processes is important for understanding flow and transport within rocks on a larger scale. Flow experiments on small-scale micromodels can be used to experimentally investigate pore-scale flow. Current manufacturing methods of micromodels are costly and time consuming. 3D printing is an alternative method for the production of micromodels. We have been able to visualise small-scale, single-phase flow and transport processes within a 3D printed micromodel using a custom-built visualisation cell. Results have been compared with the same experiments run on a micromodel with the same geometry made from polymethyl methacrylate (PMMA, also known as Perspex). Numerical simulations of the experiments indicate that differences in experimental results between the 3D printed micromodel and the Perspex micromodel may be due to variability in print geometry and surface properties between the samples. 3D printing technology looks promising as a micromodel manufacturing method; however, further work is needed to improve the accuracy and quality of 3D printed models in terms of geometry and surface roughness.

     

Exit blade geometry and part-load performance of small axial flow propeller turbines: An experimental investigation

A detailed experimental investigation of the effects of exit blade geometry on the part-load performance of low-head, axial flow propeller turbines is presented. Even as these turbines find important applications in small-scale energy generation using micro-hydro, the relationship between the layout of blade profile, geometry and turbine performance continues to be poorly characterized.The experimental results presented here help understand the relationship between exit tip angle, discharge through the turbine, shaft power, and efficiency. The modification was implemented on two different propeller runners and it was found that the power and efficiency gains from decreasing the exit tip angle could be explained by a theoretical model presented here based on classical theory of turbomachines. In particular, the focus is on the behaviour of internal parameters like the runner loss coefficient, relative flow angle at exit, mean axial flow velocity and net tangential flow velocity.The study concluded that the effects of exit tip modification were significant. The introspective discussion on the theoretical model’s limitation and test facility suggests wider and continued experimentation pertaining to the internal parameters like inlet vortex profile and exit swirl profile. It also recommends thorough validation of the model and its improvement so that it can be made capable for accurate characterization of blade geometric effects.     

Impulse and mass transport in a cartilage bioreactor using the lattice Boltzmann method

Mass and Impulse transport of oxygen enriched water in cartilage cell breeding reactor are simulated using the lattice Boltzmann method (LBM). The solver is attached with a shear stress and pressure calculator to quantify the load distribution on the cells. The solver was validated using the backward-facing step flow, which is a classical benchmark of similar discrete geometry for the bioreactor. This is achieved by comparing the qualitative and quantitative results obtained by LBM with the traditional solution and experimental approach for such a problem. The D2Q9 lattice model is used to carry out the calculations for the flow field, with a first order bounce-back boundary condition. Oxygen consumption efficiency levels in the bioreactor were reported.     

Thermo-mechanical post-buckling of FGM cylindrical panels with temperature-dependent properties

This paper presents thermo-mechanical post-buckling analysis of cylindrical panels that are made of functionally graded materials (FGMs) with temperature-dependent thermo-elastic properties that are graded in the direction of thickness according to a simple power law distribution in terms of the volume fractions of the constituents. The panel is initially stressed by an axial load, and is then subjected to a uniform temperature change. The theoretical formulations are based on the classical shell theory with von-Karman–Donnell-type nonlinearity. The effect of initial geometric imperfection is also included. A differential quadrature (DQ) based semi-analytical method combined with an iteration process is employed to predict the critical buckling load (where it is applicable) and to trace the post-buckling equilibrium path of FGM cylindrical panels under thermo-mechanical loading. Numerical results are presented for panels with silicon nitride and nickel as the ceramic and metal constituents. The effects of temperature-dependent properties, volume fraction index, axial load, initial imperfection, panel geometry and boundary conditions on the thermo-mechanical post-buckling behavior are evaluated in detail through parametric studies.     

Performance of Rubberized and Hybrid Rubberized Concrete Structures under Static and Impact Load Conditions

In this study, rubberized concrete samples were prepared by partial substitution (5 %, 10 % and 20 % replacements by volume) of sand by waste crumb rubber, and tested under impact three-point bending load, as well as static load. Three types of specimens (size 50?×?100?×?500 mm) namely, plain concrete, rubberized concrete, and double layer concrete (with rubberized concrete top and plain concrete bottom) were loaded to failure in a drop-weight impact machine by subjecting to 20 N weight from a height of 300 mm, and another three similar specimens were used for the static load test. In both the tests, the load–displacement and fracture energy of each specimen were investigated. Finite-element simulations were also performed to study the dynamic behaviors of the samples, by using LUSAS V.14 software. It was noticed that, the impact tup, and inertial and bending loads increased with the increase in the percentage of sand replacement by crumb rubber. It was interesting to observe that these effects were more significant in the double layer specimen compared to the plain and rubberized concrete samples. The static peak bending load always decreased with increase of rubber in the mix. In general, the strength and energy absorbing capability of rubberized concrete was better under impact loading than under static loading. The simulated load against displacement behaviors of all the samples were validated by the experimental results.     

Mechanical characterization of anisotropic elasto-plastic materials by indentation curves only

Anisotropy, usually orthotropy, arises in structural materials, particularly metals, due to production processes like laminations and concerns primarily parameters which govern the plastic behavior. Identification of such parameters is investigated here by a novel approach with the following features: experimental data provided by indentation curves only (not by imprint geometry); indenter shape with elliptical cross-section derived from classical conical or spherical shape and optimized by sensitivity analyses; indentation test repeated in near places after indenter rotation; deterministic inverse analyses centered on discrepancy function minimization and made computationally economical by an ‘a priori’ model reduction procedure.     

Numerical and Experimental Models of the Mandible

This study aimed to validate a numerical model of an intact mandible for further development of a new TMJ implant. Numerical and experimental models of the biomechanics of the mandible were elaborated to characterize the human temporomandibular joint and to approach the development of a condyle implant. The model of the mandible was obtained through the use of a polymeric replica of a human cadaveric mandible and through 3D geometry acquisition. The three-dimensional finite element model was generated as a tetrahedral finite element mesh. The level of mesh refinement was established via a convergence test and a model with more than 50,000 degrees of freedom was required to obtain analysis accuracy. The functional loading cases included muscle loading in four different load boundary conditions. The same boundary conditions were applied to the experimental model. The strains were measured with an experimental procedure using electric resistance strain gauges applied on the external surface of the mandible. The mechanical response is shown and discussed in terms of strains, principal numerical and measured strains. This study proved that FE models of the mandible can reproduce experimental strains within an overall agreement of 10%. The FE models correctly reproduced bone strains under different load configurations and therefore can be used for the design of a novel TMJ implant considering other load configurations and bone mechanical properties.     

复合材料加筋板极限压缩承载能力可靠性分析

基于Abaqus软件用户子程序,利用渐进失效分析方法对复合材料加筋板极限压缩承载能力进行预测。算例分析表明,对于加筋板1和2,本文方法给出的极限压缩强度与实验结果的误差分别为2.53%和1.68%。在结构可靠性分析过程中,为提高计算效率,利用屈曲载荷与极限压缩强度之间的关系建立功能函数,只需对极限压缩承载能力进行一次分析。对于加筋板1和2,本文方法相对经典可靠性方法的计算误差分别为-1.04%和-1.01%,计算时间仅为经典可靠性方法的1.18%和1.66%。     

Reseach on stability of laminated composite plate under nonlinear aerodynamic load

In this paper, we propose an finite element approach based on classical plate theory to investigate the dynamic stability of a layered composite plate subject to nonlinear aerodynamic load. This study considers the influence of temperature, nonlinear geometry, and nonlinear aerodynamic load on composite plate structures simultaneously. Specifically, the present work conduct comparison the results of the critical pressure value between the nonlinear aerodynamic load and the linear aerodynamic load, thereby pointing out some necessary cases which must consider the nonlinearity of aerodynamic load for calculating the aerospace structures. We determine the critical pressure value and vibrational amplitude response of the plate by means of calculation. The outcomes of our calculations can be useful in designing and repairing body shells and wings of aircraft equipment.     

On the equivalence of slip-line fields and work principles for rigid–plastic body in plane strain

Extremum/work principles for a rigid–plastic body have been discussed in classical theory of plasticity to be of immense significance. Unfortunately, till now, these extremum theorems have been used only as a crude method of obtaining the limit load of a rigid–plastic body, using successive approximations by upper and lower bound estimates. On the other hand slip-line fields (SLF) have been extensively used not only for evaluation of limit load but also for obtaining sufficiently accurate estimates of stresses in the plastic region as well as in the vicinity of crack tip. Till now, these two methods of plastic analyses, that is, the work principles and SLF have remained more or less independent apart from the fact that both are upper bounds as they use kinematically admissible velocity fields. Recently, a new load bounding technique, modified upper bound (MUB) Approach, was proposed by Khan and Ghosh [Khan, I.A., Ghosh, A.K., 2007. A modified upper bound approach to limit analysis for plane strain deeply cracked specimens. International Journal of Solids and Structures 44 (10), 3114–3135]. In this article, a rigorous mathematical basis of this load bounding technique is presented and it is demonstrated that the method is actually a new form of the general extremum/work principles. The equivalence of this new form of work principle, that is, MUB with the classical SLF analysis, for a rigid–plastic material in plane strain, has been discussed in detail. Since plastic deformation fields depend on specimen geometry and type of loading specific cases have been considered. Both cracked and uncracked configurations have been analysed to establish this equivalence in general. Various simplifications resulting from the use of this new load bounding technique over SLF method has been demonstrated. Several standard problems of plane strain analysed by SLF method and validated by experiments in past have been considered in this article. As a novel application of the proposed method, single-edge-cracked plate under combined bending and tensile load has been analysed. For this specimen SLF solutions are available only for bending with small tensile load (defined in Section 3.2.4) while classical upper bound solutions are valid for bending with large tensile load. In this work a completely analytical formulation for yield locus for the entire range of tensile and bending load has been obtained. Apart from accurate evaluation of limit load, detailed evaluation of crack tip stresses and hence constraint near the crack tip has been performed using this new form of work principles.     

Analysis of Slot Orientation in Shear-Compression Specimen (SCS)

This paper presents an analytical treatment as well as experimental measurement of the plastic deformation field in shear-compression specimen (SCS) by using digital image processing (DIC) technique. The results provide a set of useful expressions that relates externally applied displacement and load quantities to the equivalent stress and equivalent plastic strain within the gage section. Based on the analysis, we propose modifying the slot angle of SCS geometry from its original value of 45º to 35.26º in order to enhance the uniformity of stress and strain fields in gage section. It is shown by analysis that this enhancement is essentially because the compatibility and boundary conditions that yield a homogeneous deformation field is naturally satisfied for the particular slot orientation of ???=?35.26°. This conclusion is also supported by experimental evidence that comparatively shows the edge effects for varying slot angles.     

汽车薄钢板应力应变曲线及屈服轨迹的研究

采用十字形双向拉伸的实验方法对两种汽车用薄钢板BH220和SPEN进行了不同 加载路径下的双向拉伸试验，得到了不同应力状态下的应力应变关系曲线，同时，根据单位 体积塑性功相等的原则，确定了两种钢板等效塑性应变从0.2\%$\sim$2\%的实验屈服轨迹. 结果分析表明：不同加载路径下板料的应力应变关系不同，随着加载比例由单拉到等双拉状 态，板料的硬化指数逐步增大；实验屈服轨迹呈外凸性，且以等双拉为界的上下部分屈服轨 迹不对称，随着变形程度的增加，屈服轨迹向外扩大，但单拉时强化程度最小，而等双拉 时最大. 对BH220和SPEN钢板的实验屈服轨迹与几种常用理论屈服轨迹的比较发现，Hosford各向 异性屈服准则的理论轨迹与实验结果最为接近，Hill48准则与实验结果相差最大，此外一 向被视为只适用于各向同性材料的Mises准则与实验结果也较为接近，其他几个屈服准则的 理论屈服轨迹与实验点相差较大.     

Shock waves from an open-ended shock tube with different shapes

A new method for decreasing the attenuation of a shock wave emerging from an open-ended shock tube exit into a large free space has been developed to improve the shock wave technique for cleaning deposits on the surfaces in industrial equipments by changing the tube exit geometry. Three tube exits (the simple tube exit, a tube exit with ring and a coaxial tube exit) were used to study the propagation processes of the shock waves. The detailed flow features were experimentally investigated by use of a two-dimensional color schlieren method and by pressure measurements. By comparing the results for different tube exits, it is shown that the expansion of the shock waves near the mouth can be restricted by using the tube exit with ring or the coaxial tube exit. Thus, the attenuation of the shock waves is reduced. The time histories of overpressure have illustrated that the best results are obtained for the coaxial tube exit. But the pressure signals for the tube exit with ring showed comparable results with the advantage of a relatively simple geometry. The flow structures of diffracting shock waves have also been simulated by using an upwind finite volume scheme based on a high order extension of Godunov's method as well as an adaptive unstructured triangular mesh refinement/unrefinement algorithm. The numberical results agree remarkably with the experimental ones.     

On the experimental determination of some mechanical properties of porcine periodontal ligament

This work analyzes some aspects of the experimental determination of the mechanical properties of the periodontal ligament (PDL). The necessity of extracting small samples, with a geometry as regular as possible, from a complex biological structure, makes it quite difficult both to establish a correct testing protocol and to obtain reliable results, for instance usable by bioengineers to develop constitutive models. Here, by means of more than 250 experiments performed on small samples of porcine PDL, we try both to provide some statistically significant information, and to clarify some issues related to the testing protocols. Some basic mechanical parameters for the PDL (Young’s modulus, shear modulus, failure stress and strain for tension, compression, and shear tests) are measured, and a relevant statistical analysis is provided. The influence of some experimental parameters (sample conservation procedure, testing modalities), is also studied; on the basis of our results, we can conclude that (i) if conservation is needed, a cooling at −80° is sufficient to guarantee statistically significant results, (ii) it is important to perform at least the compression tests keeping the samples immersed in pressurized fluid, and (iii) preconditioning cycles are necessary only for studying the initial (toe) region of the stress–strain curves. It is also observed that, with these types of samples, some special care is required when computing stresses and strains from force and displacement measurements. In order to illustrate this aspect, some non-linear Finite Element analyses are performed, aimed at evaluating the influence of the sample geometry on the stress and strain calculation. Finally, the issue of fiber damage due to the cutting procedures is briefly discussed.     

Experimental characterization of non-linear behavior of monolithic glass

This paper presents the results of a combined experimental and analytical study on one-dimensional slender elements of monolithic glass subjected to simultaneous compression and bending, which progressively increased up to the collapse. The experiments were performed on 32 quintuplets; each quintuplet was composed of five identical specimens, while the quintuplets differed from each other in the geometry and glass of the specimens. The load and restraints applied to a specimen of a quintuplet were different from those applied to the other specimens of the same quintuplet; hence, five different types of tests were performed on the 160 specimens. In each test, the load and the displacements were measured continuously.The collapse, which occurred when the maximum tensile stress reached glass tensile strength (first cracking), exhibited large deflections. Cracking always initiated away from the edges, since the tests had been designed to avoid edge effects. The results proved that geometric non-linear behavior of glass members cannot be described using the same model as steel structures. An analytical model was then constructed to describe the behavior of glass members subjected to combined compression and bending, which predicts the load-carrying capacity and allows safety to be assessed.     

An experimental study on an oscillating loop heat pipe consisting of three interconnected columns

This paper presents some experimental results of an extensive research on a novel oscillating heat pipe. The heat pipe is formed of three interconnected columns as different from the pulsating heat pipe designs. The dimensions of the heat pipe considered in this study are large enough to neglect the effect of capillary forces. Thus, the self-oscillation of the system is driven by the gravitational force and the phase lag between the evaporation and condensation processes. The overall heat transfer coefficient is found to be approximately constant irrespective of heat load for the experimental cases considered. The results are also compared with the previously published data by other investigators for water as the working fluid and for the same heat input range. The experimental data for the time variation of the liquid column heights and the vapor pressure are correlated algebraically, convenient for practical uses.     

Buckling of a stiff film bound to a compliant substrate—Part I:: Formulation, linear stability of cylindrical patterns, secondary bifurcations

The buckling of a thin elastic film bound to a compliant substrate is studied: we analyze the different patterns that arise as a function of the biaxial residual compressive stress in the film. We first clarify the boundary conditions to be used at the interface between film and substrate. We carry out the linear stability analysis of the classical pattern made of straight stripes, and point out secondary instabilities leading to the formation of undulating stripes, varicose, checkerboard or hexagonal patterns. Straight stripes are found to be stable in a narrow window of load parameters only. We present a weakly nonlinear post-buckling analysis of these patterns: for equi-biaxial residual compression, straight wrinkles are never stable and square checkerboard patterns are found to be optimal just above threshold; for anisotropic residual compression, straight wrinkles are present above a primary threshold and soon become unstable with respect to undulating stripes. These results account for many of the previously published experimental or numerical results on this geometry.     

Adiabatic shear banding and scaling laws in chip formation with application to cutting of Ti–6Al–4V

The phenomenon of adiabatic shear banding is analyzed theoretically in the context of metal cutting. The mechanisms of material weakening that are accounted for are (i) thermal softening and (ii) material failure related to a critical value of the accumulated plastic strain. Orthogonal cutting is viewed as a unique configuration where adiabatic shear bands can be experimentally produced under well controlled loading conditions by individually tuning the cutting speed, the feed (uncut chip thickness) and the tool geometry. The role of cutting conditions on adiabatic shear banding and chip serration is investigated by combining finite element calculations and analytical modeling. This leads to the characterization and classification of different regimes of shear banding and the determination of scaling laws which involve dimensionless parameters representative of thermal and inertia effects. The analysis gives new insights into the physical aspects of plastic flow instability in chip formation. The originality with respect to classical works on adiabatic shear banding stems from the various facets of cutting conditions that influence shear banding and from the specific role exercised by convective flow on the evolution of shear bands. Shear bands are generated at the tool tip and propagate towards the chip free surface. They grow within the chip formation region while being convected away by chip flow. It is shown that important changes in the mechanism of shear banding take place when the characteristic time of shear band propagation becomes equal to a characteristic convection time. Application to Ti–6Al–4V titanium are considered and theoretical predictions are compared to available experimental data in a wide range of cutting speeds and feeds. The fundamental knowledge developed in this work is thought to be useful not only for the understanding of metal cutting processes but also, by analogy, to similar problems where convective flow is also interfering with adiabatic shear banding as in impact mechanics and perforation processes. In that perspective, cutting speeds higher than those usually encountered in machining operations have been also explored.     

Stress analysis of an orthotropic material under diametral compression

The diametral compression test is commonly used to determine the tensile strength of brittle materials. For isotropic materials a simple relation based on specimen geometry and the applied load at failure is used to calculate the tensile strength. Previous to this work the effect of material orthotropy and material orientation on the specimen stress state had not been completely determined. In this study, both isotropic and orthotropic specimens were analyzed using a finite element analysis and experimentally verified by strain gage and photoelastic measurements. Further, this work investigated the effect of the applied load area on the specimen stress state. Results of this work show that there is a significant difference between the theoretical calculations based on the assumption of material isotropy when compared to an orthotropic material. This difference can be as much as 45 percent depending on the degree of orthotropy and the orientation. It was also determined that the applied load area and material orientation significantly influence the specimen stress state. An applied load area of 8 percent of the circumference was found to reduce the stresses in the applied load region.