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Abstract: The correlation between residual stresses and the global properties from an indentation test, i.e. hardness and size of the contact area, has been studied frequently in recent years. The investigations presented have been based on experimental, theoretical and numerical methods and as a result, the basic features of the problem are fairly well understood in the case of residual equi-biaxial surface stresses. The more general case, when the principal surface stresses are not necessarily equi-biaxial, has received much less attention and it is therefore the aim of the present study to remedy this shortcoming. In doing so, qualitative results are of immediate interest in this initial study but possible ways of quantitative descriptions are also discussed for future purposes. The present analysis is based on numerical methods and in particular the finite element method (FEM) is relied upon. Classical Mises elastoplastic material behavior is assumed throughout the investigation. [Copyright &y& Elsevier]

Scratching of thin film/substrate structures is studied theoretically and numerically. The results are discussed in connection to delamination initiation and in particular subsequent growth at scratching. The material behavior of the film is described by classical elastoplasticity accounting for large deformations. The deformation of the substrate is neglected indicating that the results are pertinent to soft thin films. The numerical investigation is performed using the finite element method (FEM) and the numerical strategy is discussed in some detail. The results from this study show that delamination growth at thin film scratching is a stable feature with crack arrest occurring at a decreasing load. [ABSTRACT FROM AUTHOR]

Abstract: The correlation between residual stresses and the global properties, i.e. hardness and size of the contact area, given by a sharp indentation test have been studied quite frequently in recent years. The investigations presented have been based on experimental, theoretical and numerical methods and as a result, the basic features of the problem are now well understood. Furthermore, in this context quantitative relations, for the determination of residual stresses using sharp indentation, have been presented. Such relations have proven to be reliable in case of predominantly tensile residual stresses while the accuracy of predictions is much worse at compressive stress states. It is therefore the aim of the present study to investigate this matter in some detail and to present possible mechanisms for the difference in indentation behavior between tension and compression. Accordingly, the results are essentially qualitative but necessary and detailed investigations needed for a quantitative understanding are suggested. The present analysis is based on theoretical and numerical methods and in the latter case, the finite element method (FEM) is relied upon. Classical Mises elastoplastic material behavior is assumed throughout the investigation. [ABSTRACT FROM AUTHOR]

Scratching of thin film/substrate structures is studied theoretically and numerically. In most cases, the material behavior of the film as well as the substrate is described by classical elastoplasticity accounting for large deformations; further, pressure-sensitive flow models are considered. The main efforts are devoted toward an understanding of the influence from the film/substrate boundary on the stress distribution at scratching but for comparative reasons, scratching of homogeneous materials are also studied and pertinent results presented. Among other things, the results are discussed in relation to delamination initiation and growth at scratching. The numerical investigation is performed using the finite element method, and the numerical strategy is discussed in some detail. The most important finding given by the present study is that high shear stresses are the main driving force for delamination initiation and growth along the film/substrate interface. It was also noted that the influence from pressure-sensitive flow on the stress fields related to delamination initiation is small, both quantitatively and qualitatively. [ABSTRACT FROM AUTHOR]

Abstract: In the present paper scratching of soft thin film/substrate structures, using sharp conical indenters, is studied theoretically and numerically. For simplicity, but not out of necessity, the material behavior of the film as well as the substrate is described by classical elastoplasticity accounting for large deformations. Explicit material parameters are chosen in order to arrive at representative results as regards material behavior and indenter geometry. The main efforts are devoted towards an understanding of the influence from the film/substrate boundary on global scratching properties at different material combinations. Global quantities to be investigated include scratch hardness, contact area and apparent coefficient of friction at scratching. The numerical investigation is performed using the finite element method (FEM) and the numerical strategy is discussed in some detail. [Copyright &y& Elsevier]

Scratching of polymeric coatings on hard substrates is studied experimentally and numerically from a mechanical point of view. In particular, the behavior of local and global mechanical properties, as well as the delamination behavior, at scratching due to pressure-sensitive effects is of interest. The numerical investigation is performed using the finite element method (FEM) where pressure sensitivity is modeled using the classical Drucker-Prager plasticity model (Drucker, Prager, Q. Appl. Math., 10 157-165 (1952)) while the adhesion of the coating to the substrate is modeled as a cohesive zone where relevant model parameters are determined experimentally using the double cantilever beam test with uneven bending moments (DCB-UBM). Good correlation between experimental and numerical results were achieved and the most important finding concerns the fact that the dependence of pressure sensitivity proved to be different for different mechanical quantities. [ABSTRACT FROM AUTHOR]

Abstract: An experimental and numerical study of the scratch test performed on metals and polymers was conducted. The materials tested, being both metallic and polymeric, were related to the well known Johnson’s parameter, often used to correlate indentation experiments. The aim was to determine whether it was possible to use the numerical approach presented by Wredenberg and Larsson [F. Wredenberg, P.-L. Larsson, On the numerics and correlation of scratch testing, Journal of Mechanics of Materials and Structures 2 (2006) 573–594] to describe the scratch mechanism and of course also to investigate whether or not important scratch quantities can be determined with sufficient accuracy from standard scratch experiments. [Copyright &y& Elsevier]

Abstract: A plane strain study of wedge indentation of a thin film on a substrate is performed. The film is modelled with the strain gradient plasticity theory by Gudmundson [Gudmundson, P., 2004. A unified treatment of strain gradient plasticity. Journal of the Mechanics and Physics of Solids 52, 1379–1406] and analysed using finite element simulations. Several trends that have been experimentally observed elsewhere are captured in the predictions of the mechanical behaviour of the thin film. Such trends include increased hardness at shallow depths due to gradient effects as well as increased hardness at larger depths due to the influence of the substrate. In between, a plateau is found which is observed to scale linearly with the material length scale parameter. It is shown that the degree of hardening of the material has a strong influence on the substrate effect, where a high hardening modulus gives a larger impact on this effect. Furthermore, pile-up deformation dominated by plasticity at small values of the internal length scale parameter is turned into sink-in deformation where plasticity is suppressed for larger values of the length scale parameter. Finally, it is demonstrated that the effect of substrate compliance has a significant effect on the hardness predictions if the effective stiffness of the substrate is of the same order as the stiffness of the film. [Copyright &y& Elsevier]

Abstract: Friction has a profound influence on Hertzian fracture initiation when dissimilar materials are involved. Experimental studies show that the presence of friction results in higher fracture loads and fracture radii as compared to the frictionless case. It has also been shown recently that the experimental observations concerning Hertzian fracture initiation at unloading may be explained by the effect friction has on a surface tensile stress distribution. Presently a contact cycle between two dissimilar elastic bodies at finite Coulomb friction has been investigated numerically for a wide range of material parameters and contact geometries. Emphasis has been given to the surface tensile stress distribution which is assumed to be a governing parameter for Hertzian fracture initiation. In particular it was found that during loading the contact region divides into invariant stick and inward slip regions and the presence of outward frictional shear tractions reduces the maximum surface tensile stress and shifts it away from the contact contour as compared to the frictionless case. At unloading, the distributions of stick-slip zones were found to be severely history- and geometry-dependent and shear tractions reversed their direction over part of the contact area. Consequently, tensile stresses were found to grow at unloading. Results concerning the influence of the friction coefficient, Dundur''s parameter and the specimen''s Poisson''s ratio on the absolute maximum surface tensile stress obtained at a frictional contact cycle are reported along with the magnitudes of the relative increase of maximum tensile stresses at unloading. Based on a critical stress fracture criterion it is discussed how the predicted increases will influence the critical loads required for crack initiation. [Copyright &y& Elsevier]

Abstract: In this review article similarity methods for analysing indentation contact problems are explored and related advantages and disadvantages discussed in some detail. In particular, combined elastic and plastic effects, together with, and also taken separately from, the influence from large deformations, are discussed in the context of a self-similarity analysis. The main conclusion of the present investigation is that a self-similarity approach to indentation problems is of significant advantage at many circumstances while, however, limitations of such methods have to be carefully accounted for at application. [Copyright &y& Elsevier]

Abstract: The influence of indenter elasticity on Hertzian fracture initiation at frictional dissimilar elastic contact has been examined experimentally and numerically. In flat float glass specimens initiation of cone cracks has been observed and fracture loads measured with steel and tungsten carbide indenters at monotonically increasing loading and during a load cycle. The observed effect of indenter elasticity on fracture loads was found to be qualitatively different from the one predicted by the Hertz contact theory. This discrepancy may be explained by the presence of interfacial friction. The friction coefficient between the indenters and the specimen was measured and a contact cycle at finite Coulomb friction has been analyzed numerically. The influence of the indenter elasticity and the friction coefficient on the surface maximum tensile stress has been investigated and the results concerning the influence of these parameters on the fracture loads as given based on a critical stress fracture criterion. The obtained computational results were found to be in better agreement with experimental findings as compared to the predictions based on the frictionless contact theory. A remaining quantitative discrepancy was attributed to the well-known fact that a Hertzian macro-crack initiates from pre-existing defects on the specimen’s surface. In order to account for the influence of the random distribution of these defects a Weibull statistics was introduced. The predicted critical loads corresponding to the 50% failure probability were found to be in close agreement with experimentally observed ones. [Copyright &y& Elsevier]

Abstract: In two previous articles by Carlsson and Larsson [S. Carlsson, P.-L. Larsson, On the determination of residual stress and strain fields by sharp indentation testing. Part I. Theoretical and numerical analysis, Acta Mater., 49 (2001) 2179–2191; S. Carlsson, P.-L. Larsson, On the determination of residual stress and strain fields by sharp indentation testing. Part II. Experimental investigation, Acta Mater, 49 (2001) 2193–2203], sharp indentation tests were analysed experimentally, theoretically and numerically and it was found that biaxial residual stress and strain fields could be correlated with the global properties, i.e. hardness and size of the contact area, given by such tests. The practical usefulness of this finding is limited though due to the fact that the global properties are only weakly dependent of the residual stress state when standard indenter geometries are at issue. In order to find some guidance for improving upon this situation a numerical study of sharp indentation testing, based on the finite element method, was performed. The results derived indicate that the sensitivity of indentation variables to stress can be significantly increased by increasing the inclined angle of the sharp indenter and that this feature can be accurately captured by previously derived closed form relations directly applicable to a practical situation. [Copyright &y& Elsevier]

Abstract: The local contact behaviour of composite powders arranged in regular lattices has been investigated in this study with the finite element method. Numerical results related to isostatic and die compaction of unit cells of simple cubic and body-centered cubic lattices have been compared to previous analytical and numerical findings describing in particular local but also global contact at powder compaction. The finite element calculations are continued up to full density of solid material in the unit cells. [Copyright &y& Elsevier]

Microindentation as a method for determining important material properties of paper coating materials is studied experimentally and numerically. The bulk of the investigation is concentrated upon the short-lived elastic part of a spherical indentation test, but determination of the failure stress of the coating is also discussed. The results indicate that microindentation can be a powerful tool for material characterization of these materials, but only if careful efforts are made to account for the influence from plasticity as well as from boundary effects. [ABSTRACT FROM AUTHOR]

Cold compaction of composite powders with size ratio has been analysed in this study using a discrete element method. Powder aggregates consisting of up to 10,000 particles and formed by two powder populations with known material strength and size ratios have been compacted both isostatically and uniaxially. The particles were assumed constitutively to be either perfectly plastic or rigid, and as a result, local contacts between the particles were described by a linear force–displacement relation. The results of this study include the presentation of relevant compaction quantities as a function of densification, and a detailed comparison with previous theoretical, numerical, and experimental studies. Particular emphasis has been placed on investigating the predictive capability of the fundamental assumptions frequently used in theoretical analyses of compaction problems. [Copyright &y& Elsevier]

This study aims to provide a thermophysical characterization of a new economical and green mortar. This material is characterized by partially replacing the cement with recycled soda lime glass. The cement was partially substituted (10, 20, 30, 40, 50 and 60% in weight) by glass powder with a water/cement ratio of 0.4. The glass powder and four of the seven samples were analyzed using a scanning electron microscope (SEM). The thermophysical properties, such as thermal conductivity and volumetric specific heat, were experimentally measured in both dry and wet (water saturated) states. These properties were determined as a function of the glass powder percentage by using a CT-Meter at different temperatures (20 °C, 30 °C, 40 °C and 50 °C) in a temperature-controlled box. The results show that the thermophysical parameters decreased linearly when 60% glass powder was added to cement mortar: 37% for thermal conductivity, 18% for volumetric specific heat and 22% for thermal diffusivity. The density of the mortar also decreased by about 11% in dry state and 5% in wet state. The use of waste glass powder as a cement replacement affects the thermophysical properties of cement mortar due to its porosity as compared with the control mortar. The results indicate that thermal conductivity and volumetric specific heat increases with temperature increase and/or the substitution rate decrease. Therefore, the addition of waste glass powder can significantly affect the thermophysical properties of ordinary cement mortar. [ABSTRACT FROM AUTHOR]

Correlation of sharp indentation problems is examined theoretically and numerically. The analysis focuses on elastic-plastic pressure-sensitive materials and especially the case when the local plastic zone is so large that elastic effects on the mean contact pressure will be small or negligible as is the case for engineering metals and alloys. The results from the theoretical analysis indicate that the effect from pressure-sensitivity and plastic strain-hardening are separable at correlation of hardness values. This is confirmed using finite element methods and closed-form formulas are presented representing a pressure-sensitive counterpart to the Tabor formula at von Mises plasticity. The situation for the relative contact area is more complicated as also discussed. [ABSTRACT FROM AUTHOR]

The search for environmental preservation and conservation of natural resources gives rise to new concepts and viable technical solutions on the path to sustainable development. In this context, this study's main objective is to analyse the influence of recycled concrete aggregates (RCAs) on the development of pervious concrete, whose use as a floor covering represents an excellent device to mitigate the urban soil sealing phenomena. For this, mechanical and hydraulic tests were carried out, in addition to microstructural analyses and the assessment of its environmental performance. The results obtained were compared to reference studies also involving the incorporation of recycled aggregates. A pilot-scale case study was conducted, involving a parking space lined with pervious concrete moulded "in situ". In laboratory tests, permeability coefficients and mechanical strengths compatible with the literature and above the normative limit for light traffic were found. The case study demonstrated higher permeability than in the laboratory, but the flexural strength was lower, being indicated only for pedestrian traffic. The environmental assessment showed that the RCA represents a positive contribution to the environmental performance of pervious concrete. Still, attention should be given to the recycled aggregate transport distance between the concrete plant and the RCA treatment plant. [ABSTRACT FROM AUTHOR]

The rock fragmentation response to drilling, in particular percussive drilling, is important in order to improve the efficiency of such an operation. The resulting problem includes spherical contact between the drill bit and the material and therefore, a numerical analysis of frictional effects in quasi-static spherical indentation of Bohus granite is presented. The frictional coefficient between the indenter and the granite surface is accounted for in numerical simulations. A previously determined constitutive law is used for the purpose of numerical analyses. The latter consists of a Drucker-Prager plasticity model with variable dilation angle coupled with an anisotropic damage model. Since the tensile strength is random, Weibull statistics was considered. Using a frictionless contact model, the stress state of Bohus granite corresponding to the first material failure occurrence, observed in indentation experiments, was numerically determined. However, the frictional effects, which are of interest in this study, may lead to changes in the numerically established stress state and consequently the Weibull parameters should be recalibrated. The so-called Weibull stress decreases from 120 MPa for a frictionless contact to 75 MPa for frictional contact, and the Weibull modulus from 24 to 12. It is numerically observed that the predicted force-penetration response, using the new set of Weibull parameters, is not influenced by friction. Conversely, the predicted fracture pattern, in the case of frictional contact, is similar to the case of frictionless contact, but its size is somewhat larger. Last, a parametric study analyzing the dependence of the friction coefficient is carried out and no significant changes are detected. The novelty of the present findings concerns the fact that both an advanced damage description in combination with an advanced plasticity model, both implemented for finite element analyses, is used to analyze frictional effects at granite indentation. [ABSTRACT FROM AUTHOR]

The material parameter L should in the text, Table 1, and Figures 8 and 9 have the notation L/X. In Figure 1 and the equations, the parameter L is defined correctly. [ABSTRACT FROM AUTHOR]

The determination of residual stresses is an important issue when it comes to material failure analysis. The variation of global indentation properties, due to the presence of residual stresses, can serve as a guideline for the size and direction of such stresses. One of these global indentation properties, the material hardness, is unfortunately invariant of residual stresses when metals and alloys are at issue. In this situation, one has to rely on the size of the indentation contact area for residual stress determination. For other materials such as ceramics and polymers, where elastic deformations are of greater importance at indentation, such invariance is no longer present. Here, this variation is investigated based on finite element simulations. The aim is then to determine how the indentation hardness is influenced by the principal residual stress ratio and also discuss if such an influence is sufficient in order to determine the size and direction of such stresses in an experimental situation. It should be emphasized that this work does not suggest a new approach to residual stress determination (by indentation testing) but investigates the applicability of previously derived methods to a situation where the surface stress field is not simplified as equi-biaxial or uniaxial. For simplicity, but not out of necessity, only cone indentation of elastic-perfectly plastic materials is considered. [ABSTRACT FROM AUTHOR]

Evaluation and correlation of global quantities, i.e., normal and tangential hardness, at scratch testing in the context of a representative stress description was investigated. In particular, verification based on experimental results is at issue. It has been shown previously that within the framework of classical von Mises elasto-plasticity and quasi-static conditions, correlation can be achieved by using a combination of stresses at different levels of plastic strains to define representative quantities at scratching, accounting for the difference in mechanical behavior at elasto-plastic and rigid plastic scratching. However, verification from experimental results is required, which has been attempted in this study. Predictions based on previous theoretical results were compared with experimental findings for polymeric materials, as well as for different metals. Good agreement was found between the two sets of results, particularly so for the case of polymers modelled by von Mises elasto-plasticity. Accordingly, these results are of direct practical, accurate, and novel relevance for semi-crystalline polymers where viscoelastic effects are negligible. [ABSTRACT FROM AUTHOR]

Scratch testing is a contact mechanics based nondestructive testing method that, if correctly evaluated, can give a lot of information about the material and tribological behavior of a material. In contrast to the situation with another contact-based method, indentation testing, wear characteristics can also be investigated, for example. In order to get results of practical importance from a scratch test, it is necessary to have evaluation formulae available. Indeed, such formulae exist for scratch testing but can be substantially influenced by frictional effects. For this reason, closed-form analytical relations have been suggested for the purpose of accounting for such effects during scratching and in particular the plowing frictional effect. As a major benefit, these relations can also be of assistance during material characterization through scratch testing. However, the proposed existing relations are based solely on theoretical/numerical analyses and, remembering that the scratch test of course is an experimental approach, verification by experiments is a necessity. Such a task is performed in the present study and it is shown that, based on standard contact global properties, the relations are accurate for most polymeric materials but could also be used for some metallic ones. [ABSTRACT FROM AUTHOR]

Material parameter curves in an advanced material model describing compaction of spray dried cemented carbide powder are determined successfully based on a general approach for material characterization of powder materials. Pressing forces from a production machine and equivalent finite element (FE) calculations are used in inverse modelling. A pressing method that includes multiple unloading steps is used. The material model is of Drucker Prager CAP kind and friction between powder and pressing tool is modelled as a function of normal pressure. The results are verified with density gradient measurements using a neutron source. The method is proven to be robust and the results show good agreement between experiment and simulation. Effects that have not been captured numerically previously are captured due to the high accuracy of material characterization. The present approach is detailed for tungsten carbide powders but is valid for other powder materials when properly calibrated for constitutive and frictional effects in the same manner as outlined here. Unlabelled Image • Pressing forces from experiments in a regular production machine is applied to reverse engineering. • A pressing cycle with multiple unloading steps is developed. • Density dependent bulk modulus and hydrostatic failure is determined successfully. • FE simulations include a frictional model that is dependent on normal pressure. • The results are verified with density measurements using a neutron source. [ABSTRACT FROM AUTHOR]

Density variations in pressed powder materials are of substantial importance and will affect shrinkage and geometry after sintering. It is therefore important to accurately measure this quantity in green bodies. This is emphasised by the fact that the density variation can be used for determining material properties in constitutive mechanical models of compaction. An obvious method to determine the density variation is X-ray tomography. For cemented carbides this is not a possible alternative due to the very high X-ray absorption of tungsten making the samples impossible to penetrate. Neutron radiation has a much higher penetration and this suggests that a neutron source could be used for density distribution determination in such materials. This was investigated currently showing promising results when compared with finite element predictions. It is clear that this approach must be improved to be able to use neutron radiation as a tool for density determination. Improvements are suggested. [ABSTRACT FROM AUTHOR]

The focus in this work is toward an investigation of the fracture response of brittle materials with different specimen size loaded in diametral compression using different boundary conditions. The compacted zone underneath the loading points is assumed to be limited and only responsible for the load transition to the rest of the material. Therefore, the theory of elasticity is used to define the stress state within a circular specimen. A tensile failure criterion is used, and the final load capacity is related to the formation of a subsurface crack initiated in a probabilistic manner in a region in the vicinity of the loaded diameter of the specimen. This process is described by Weibull theory, and it is assumed here that the growth of the subsurface crack occurs in an unstable manner. Therefore, the assumption in Weibull theory that the final failure occurs as soon as a macroscopic fracture initiates from a microcrack is fulfilled. The concept of disk effective volume used in Weibull size effect is presented in a convenient way that facilitates the application of the model to transfer the tensile strength obtained from different methods such as three point bending and Brazilian test. The experimental results for Brazilian test on a selected hard rock are taken from the literature and a fairly close agreement is obtained with the model predictions. [ABSTRACT FROM AUTHOR]

An anisotropic damage model is employed in order to simulate the fracture pattern of Bohus granite under quasi‐static (Q‐S) spherical indentation loading. The chosen damage description is added to the previously employed Drucker–Prager (DP) plasticity model with variable dilation angle. The resulting constitutive model is implemented to simulate the behavior of Bohus granite under indentation up to the load capacity of the material. The initial fragmentation, corresponding to the first small load‐drop in the force–penetration curve, is likely due to the high radial tensile stress state at or close to the contact boundary. Both predicted fracture pattern and force–penetration results from the numerical simulation are compared to experimental data and a good agreement is found. The variability in tensile strength of the material is included in the chosen damage model by taking advantage of Weibull statistics. In this work, it is suggested that indentation test results by themselves may be used to calibrate the statistical distribution of tensile strength at small size scales such as in indentation applications. [ABSTRACT FROM AUTHOR]

One of the characteristic features of sintered steels is the porosity in their microstructure resulting from the compaction and sintering process. This porosity strongly influences the mechanical properties. To enhance the understanding for the structure–property relationship of sintered Astaloy®85Mo with 0.4 wt.%C, a micromechanical modelling approach based on face-centred cubic (fcc) representative volume elements (RVE) is proposed. The fcc-like periodic arrangement of the sintered particles in the RVE enables the consideration of a realistic non-spherical pore morphology. To compare the predictions with experimental results, accompanying uniaxial tensile tests are considered at different pore volume fractions after initial microstructure characterisation. In addition to the effect of pore volume fraction, the influence of sinter necks on the predicted overall strength is also systematically investigated. Despite the fairly simple nature of the underlying fcc structure, the RVE simulations are perfectly capable of reproducing the experimental trend, showing that the elasto-plastic properties decrease with increasing porosity. This is in contrast to analytical predictions, which underestimate the decrease in properties due to spherical pore assumptions. Moreover, the finite element-based simulations reveal a less pronounced influence of the sinter neck shape on the macroscopic behaviour, even though substantial differences in plastic strain localisation are discernible at the microscopic scale. • Micromechanical model proposed for porous sintered steels based on 3D RVEs. • Fcc-like periodic particle arrangement enables a non-spherical pore morphology. • RVE simulations are perfectly capable of reproducing the experimental trend. • Sinter neck shape hardly affects the macroscopic, but microscopic behaviour. [Display omitted] [ABSTRACT FROM AUTHOR]

Spray-dried refractory carbide and metal powder mixtures, containing tungsten carbide, is compacted and sintered during the production of conventional cutting tool inserts. Since friction between the pressing tool and the powder gives rise to density gradients in the powder compact, shrinkage during sintering is uneven. The shape of the sintered blank is important and can be predicted with finite element (FE) simulations. To validate the simulation of the pressing procedure, the density gradients in the powder compacts must be measured with a high spatial resolution. Since tungsten has a high atomic number, it is hard to penetrate with X-rays and even cold neutrons. We show here that by using a polychromatic beam of thermal neutrons, along with beam-hardening correction, such measurements can be successfully realized. The obtained results show good agreement with corresponding FE-simulations. Also, deliberate differences in the compaction process could be verified with the neutron measurements. Unlabelled Image • For the first time, density distributions in cemented carbide compacts are measured. • Good agreement is found between measurements and FEM-simulations. • Process characteristics related to rate-dependence and creep are determined. [ABSTRACT FROM AUTHOR]

Performance of stone-based construction materials, such as asphalt and unbound aggregate mixtures is defined to a great extent by the mechanics of the stone-to-stone interactions. Accordingly, the Discrete Element Method (DEM) is gaining popularity as a modelling tool to investigate the mechanical behavior of these materials. Contact and failure laws defining particles force-displacement relationships and the propensity of particles to break are crucial inputs for the DEM simulations. The present study aims at providing an experimental contact mechanics basis for the development of physically based stone-to-stone interaction laws. The attention is focused on investigating stone's force-displacement relationship and damage characteristics at pure normal loading for two stone materials used by the road industry. Experiments are performed at spherical contact profiles for cyclic and monotonically increasing loads. The emphasis lies on the evolution of contact compliance and accumulation of contact induced damage. The effect of surface roughness on the materials response is examined through comparative experiments performed on the specimens with different roughness values. Optical and environmental scanning electron microscopy (ESEM) observations of the contact induced damage at the material surface are presented and discussed in the context of contact mechanics. The implications of the reported experimental findings on the development of mechanics based contact and failure laws for the DEM modelling of stone-based construction materials are discussed. [ABSTRACT FROM AUTHOR]

This study focuses on an inverse modelling approach, using FEM to simulate the sintering of WC-Co powder using a continuum model. From a previously developed constitutive model of cemented carbide, the dependency of the material parameters is investigated in a sensitivity study. A value of sensitivity is assigned to all the material parameters and calculated at different steps in the sintering process, which represent its importance for capturing the shrinkage during sintering. The approach is that only the more sensitive parameters should be fitted when changing experimental setup or material composition, leaving the less important parameters constant, resulting in fewer tests and iterations. This approach is tested in an optimization of WC-Co powder sintering cycle, where the shrinkage curve is experimentally determined. It is concluded that some of the material parameters play a minor role in the modelling and could be set as constants in an optimization. The constitutive material model alone is unable to capture all features that appeared in the shrinkage curve during the experiment. Improvements of the model are discussed. An additional investigation, performed without heating rate dependency, shows that the remaining material parameters could compensate for the omitted heating rate for a known sintering cycle without losing accuracy. [Display omitted] • The number of adjustable parameters can be reduced when simulating sintering. • The sensitivity of a parameter changes in the different stages of sintering • The thermal strain rate can be omitted by compensating its contribution. • The shrinkage starts earlier in the experiments than what is possible to simulate. [ABSTRACT FROM AUTHOR]

Astaloy™ 85 Mo is a pre-alloyed, water-atomized 0.85% Mo steel powder. The aim of the present investigation is to study the influence of porosity, controlled by both mechanical and thermal processing, on the mechanical properties in a bainitic microstructure of a pressed and sintered steel. To achieve this, uniaxial tensile and compression testing is performed, together with Vickers macro- and microhardness experiments. Microhardness testing is carried out in order to determine the behavior of the matrix material at a scale where porosity influence is minimized. Both the influence from size and shape of the pores is investigated and compared with relevant mechanical analyses for porous solids. Such mechanical analyses are pertinent to both elastic and plastic properties, where in the latter case the well-known Gurson-Tvergaard model for solids with spherical pores is relied upon. It is shown that assuming a spherical pore shape is not sufficient in order to achieve good agreement between predictions and experimental results and will be further investigated in future studies. [ABSTRACT FROM AUTHOR]