Papers by Keyword: Indentation

Abstract: An extensive experimental work of instrumented indentation on isolated particles of Non-Hazardous Waste Incineration bottom ash (NHWI) is presented in this paper. The aggregates studied come from the Garenne quarries at Vignoc (Brittany, France). Two spherical tungsten carbide indenters of respective 0.5 and 140 mm radius “R” were used for test series “A” and “B”. The particles studied have diameters ranging between 20 and 25 mm. With a 0.5 mm radius indenter, average reduced elastic moduli ranging from 15 to 68 GPa were found. An average reduced elastic modulus of 15 GPa was found with the 140 mm radius indenter. The experiments made it possible to highlight the particular heterogeneity that characterizes the rigidity of the types of aggregates studied.

Abstract: Various impact analysis models have been used for analytical prediction of peeningresidual stress. In this paper, a new approach based on finite element (FE) analysis was proposed topredict the peening residual stress through single indentation analysis using the dent profilegenerated on a shot-peened surface. Three analysis models (rigid, elastic, and plastic shots) werecompared each other, and the dent obtained in the plastic shot impact analysis model showed a dentprofile almost identical to that of the experimentally obtained dent. A rigid indenter modelconstructed using the dent profile obtained by dynamic impact analysis, and it integrated into thesingle indentation analysis model. The FE surface residual stress obtained in the center of the dentof the indentation analysis model was found to be almost identical to the surface residual stressmeasured by X-ray diffraction (XRD), thus verifying the validity of the proposed single basicindentation FE model based on impact analysis.

Abstract: As shot peening is widely used to improve the crack resistance of various metals, it isimportant to have an accurate method to calculate the compressive residual stress produced by thisprocess. To this end, this paper presents a finite element (FE) model that includes an indenterdesigned from a dent profile. The results of compressive residual stress obtained by using thisindenter model and a normal shot impact model are compared. The indentation FE solution with anunmodified indenter is close to that obtained using the rigid shot (RS) impact model. The solutionfor the indentation FE model with a modified indenter closely matches that for an elasticdeformable shot (EDS) impact model. These results confirm the effectiveness of the indentation FEmodel based on the dent profile. This model can replace the present impact FE models to calculatethe compressive residual stress produced by shot peening.

Abstract: The aim of this work is indentation study of local mechanical properties of Cu-22Zn-4.6Al alloy, which has significant shape memory effect after quenching from dual α + β phase region. The study was carried out on the samples with thermoelastic and non-thermoelastic martensite in the structure, which were obtained by quenching from various temperatures. A different behavior concerning mechanical properties measurements of α phase and β phase transformed to martensite after quenching from various temperatures was found out. It was observed almost no change of mechanical properties of α phase, whereas indentation hardness H_IT and indentation modulus E_IT raised with increasing quenching temperature. Also some serious differences were observed at indentation test of thermoelastic and non-thermoelastic martensite.

Abstract: In the practice of civil engineering, the methods of impact diagnostics of materials find their application, allowing quickly and accurately measure the required strength characteristics at any point in the structure. Impact methods offer many advantages, for example, at smaller dimensions can be developed big the contact force, it can be recorded more information about the response of the material to dynamic impact and others. This approach is widely used in determining the hardness of materials and makes it possible to determine the complex mechanical characteristics: yield strength, ultimate strength, and elongation. In the paper we consider the axisymmetric problem of the impact of the conical indenter on the plate, laying on Winkler Foundation under elastic-plastic deformation. The solution is based on the phenomenological model of elastic-plastic indentation in a quasistatic formulation. The general deformations of the plate are considered elastic, and the local, in the contact zone, are elastoplastic. The main characteristics of the impact are determined: the force of the contact interaction, the local indentation, the contact time. The device and methods of determining the strength characteristics of plates under specified conditions of impact were developed on the basis of obtained solutions. The proposed method has been tested on many building structures: bridges, trusses, structural structures of artificial structures, reinforcement bars, welded joints.

Abstract: Ferritic ductile cast iron (FDI) microstructure is composed by graphite nodules embedded in a ferritic matrix. It is usual to assume that the ferritic matrix is homogeneous. However, the experimental analysis shows impurities and in some cases a high degree of heterogeneity. It is necessary to investigate the influence of these heterogeneities on the mechanical properties of FDI.This work focusses on the characterization of the elastoplastic properties of different zones of the ferritic matrix of FDI and the identification of the sequence and extent of the damage mechanisms at the micro-scale under uniaxial tensile loading.The methodologies for the characterization of the material micro constituents and micro-segregated zones involve nano-indentation and atomic force microscopy techniques in combination with computational modelling. The analysis is performed by applying inverse analysis algorithms proposed in the literature. The microsegregated zones are identified by using color etching. The assessment of the micro-scale damage mechanisms was performed by in-situ optical microscopy observation of tensile tests of very small specimens.The results led to the quantification of the differences in mechanical properties along the metallic matrix as a result of the existing heterogeneities and allow for a better understanding of the ductile iron damage mechanism.

Abstract: An original experimental campaign never conducted until now on Non-Hazardous Waste Incineration aggregates is presented in this paper. The experiments were conducted in two phases: Scanning Electron Microscopy (SEM) and instrumented indentation. A cartography followed by a series of Quantitative Chemical Microanalysis (QCM) was carried out on the 0/12.5 mm fraction of the particle size distribution. Instrumented indentation tests were carried out on isolated particles of 25 mm in diameter. Observations at the SEM yielded the exact chemical composition of the bottom ashes. It has been found that the proportions of the chemical elements composing the material are slightly different from those of other studies. This difference has made it possible to note that the zone of production of the bottom ash significantly influences their physicochemical characteristics. From the indentation curves obtained, the “Olivier and Pharr” method was used to determine the reduced modulus of elasticity “E_r”. Mean values of approximately 65 GPa and 40 GPa were obtained respectively for vitreous phases and less vitreous ones.

Abstract: Soft solid undergoes large deformation under external loading. In order to understand the mechanical characteristics of soft solid, a quantitative evaluation of the deformation behavior is necessary. In the previous study, a strain distribution on the surface of soft solid during an indentation (penetration) test was obtained by evaluating the deformation behavior using isoparametric finite element. However, three-dimensional deformations including out-of-plane deformation was neglected. In this study, the deformation behavior of the soft solid was analyzed using a stereo camera system and binocular disparity method. The out-of-plane deformation of the soft solid was then reconstructed three-dimensionally. Analysis result showed that this study was able to reconstruct the out-of-plane deformation in the area below the indenter. In addition, the displacements of specific points located on the deformed surface could also be estimated. Under the indentation loading condition, the out-of-plane displacements of points in the area below the indenter were estimated to be between 5.9 and 9.9 mm. However, the accuracy of the estimation should be validated by other measurement techniques in the future.

Abstract: Several investigations regarding the mechanical behaviour of composites reinforced by natural fibers under impact have been realized recently, aiming at achieve a low-weight and resistant design. At the same time, progressively accurate results on numerical simulations have been reached powered by modern Finite Element Method (FEM) approaches for composites; however, demonstrating a faithful indentation pattern is still a challenge. The present work aims at building an impact numerical simulation that exhibits a fracture mechanism exactly like the one seen in experimental tests, also carried in this work, on a Basalt Reinforced Composite Polymer (BRFP) plate subjected to low-velocity falling weight impact (IFW). The FEM simulation describes a multiphase model considering each ply and their inter-layer interactions.

Abstract: Physical phenomena in a nanometric machining process were studied by molecular dynamics simulations. A cylindrical tool was indented and then moved laterally on an initially flat workpiece. The focus of the study is on the effect of lubrication on the nanoscale. Therefore, the indentation and the scratching were studied both in vacuum and submersed in a lubricant. All materials were modeled by Lennard-Jones truncated and shifted potential sites. It is observed, that in the lubricated case, a substantial part of the cutting edge of the tool is in dry contact with the workpiece. Nevertheless, compared to the dry scenario, the lubrication lowers the coefficient of friction. However, the work which is needed for the indentation and the scratching is not reduced. The processed surface is found to be smoother in the lubricated case. As expected, the lubrication has an important influence on the temperature field observed in the simulation.