Static Indentation Research Articles

Estimation of Process Damping Coefficient Using Dynamic Cutting Force Model

A model of process damping in milling was developed in this study. The process damping is a critical parameter to increase the stable cutting region at low cutting speed to avoid chatter. The previous studies conducted experiments to estimate the process damping. Nevertheless, it is time and cost consuming. A model of dynamic cutting force was employed in this study. The plowing force generated by the flank-wave contact is considered as the main source of process damping to dissipate vibratory energy during cutting. In addition to the material properties and plowing force, the effects of chatter amplitude and wavelength, which result in the various indentation conditions and affect the coefficient of process damping, were also considered. The consideration of wavy contact surface and indentation area in this model allows quick determination of cutting stability conditions with high accuracy. The process damping coefficient estimated by the proposed model successfully represented the effect of the tool wear on chatter because of the change of tool geometry. Experiments were conducted to verify the new model.

The influence of operating temperature and bearing steel structure in shakedown of three-dimensional elastic-plastic rolling contacts

This paper describes a model for the prediction of micro-plastic material transformation and associated residual stress field development in through-hardened and case-hardened bearing steels during over-rolling, considering the influence of operating temperature. The main challenge in analysing three-dimensional elastic-plastic rolling contacts is the accurate description of material properties in case of two-phase material, either is a constant amount of retained austenite (through-hardened AISI 52100 bearing steel) or variable amount of retained austenite along depth (case-hardened steel, i. e. 16MnCr5 bearing steel). Material parameters at room temperature, 650 and 1000 C degrees were obtained by half-compressive cycles tests on an INSTRONTM apparatus with a climate cell and further verified by performing experimental and numerical analyses in case of static indentation between a ceramic ball and a flat steel plate. To check the ability of the proposed models to simulate the elastic-plastic rolling contact in various loading condition, experiments were made on a special designated test rig and recorded values were compared with the numerical simulations obtained by using a semi-analytical solver. Measurements of residual cyclic profiles and residual stresses show a good agreement with theoretical values, leading to a better understanding of the fatigue process in hardened bearing steels.

Uticaj debljine sloja na mehanizme oštećenja kompozitnih laminata pod ponavljanim opterećenjem

Barely visible impact damage (BVID) occurs in composite laminates subjected to low-velocity impact. They can then exhibit significant effect on mechanical performance of laminates. Previously, it is shown, analytically and experimentally, that BVID occurs at a critical energy level and below this energy level there is no induced damage. However, repeated impact may cause BVID even below the critical energy level. This paper is a novel investigation that deals with the cyclic behaviour of quasi-isotropic glass/epoxy laminated composites under indentation, which is a quasi-static version of low-velocity impact. In particular, this study aims to investigate the ply thickness effect on matrix crack-induced delamination damage in the case of laminated composites under cyclic quasi static indentation loadings. The effect of different parameters, such as load level and ply thickness, on the damage evolution were here investigated. Tests were performed according to the ASTM 7136 standard. Since the glass layer was translucent, it was also possible to visually inspect the matrix delamination during the tests. The laminates were subjected to load levels lower than the critical load level, while there was no evidence of damages when samples were indented just once. However, by increasing the number of cycles, matrix crack-induced delamination appeared in the samples. In brief, it was observed that the ply thickness and energy level have significant effects on the intensity of the induced damage.

Changes in the mechanical properties of femoral cartilage tissue in advanced osteoarthritis

The main goal of this article was the analysis of the changes of mechanical properties, thickness and histology of the cartilage in different regions of the femur head in advanced stage of the osteoarthritis. The study material consisted of cylindrical specimens (9.7 mm) prepared form proximal epiphysis of the human femur bone after hip arthroplasty. The thickness was determined from the reconstruction of the specimen from microtomography (SkyScan 1172, Bruker®) images. Mechanical properties of the cartilage tissue were identified in static indentation test conducted the use of MTS® Synergie 100 testing machine. Histological study enabled us to determine cartilage total thickness as well as location and orientation of the collagen fibers. Depending on the region of the head, the cartilage tissue thickness was in the range (0.74-2.23 mm). The lowest thickness values were obtained for the R5 region and the lowest for R4. Samples from R1-R4 regions differ by 24%. Measurements of cartilage tissue indentation, determined with the help of Hayes' formula, showed that the values of mechanical parameters in regions R1, R2, R3 and R5 have similar values (the difference between them is about 5.5%). Region R4, which had the smallest thickness, also had the lowest values of mechanical parameters. Using κ coefficients, proposed by Hayes, enabled us to obtain similar values of mechanical parameters in the regions R1, R2, R3 and R5, despite differences in cartilage tissue thickness. The R4 region, which had the weakest mechanical parameters, was characterized by the strongest reduction of the articular cartilage tissue, which was accompanied by an unformed mass of cartilage residue originating from the abraded surface and bursa fluid.

Scratching the Surface: Elastic Rotations Beneath Nanoscratch and Nanoindentation Tests

In this paper, we investigate the residual deformation field in the vicinity of nano-scratch tests using two orientations of a Berkovich tip on an (001) Cu single crystal. We compare the deformation with that from indentation, in an attempt to understand the mechanisms of deformation in tangential sliding. The lattice rotation fields are mapped experimentally using high-resolution electron backscatter diffraction (HR-EBSD) on cross-sections prepared using focused ion beam (FIB). A physically-based crystal plasticity finite element model (CPFEM) is used to simulate the lattice rotation fields, and provide insight into the 3D rotation field surrounding nano-scratch experiments, as it transitions from an initial static indentation to a steady-state scratch. The CPFEM simulations capture the experimental rotation fields with good fidelity, and show how the rotations about the scratch direction are reversed as the indenter moves away from the initial indentation.

Quasi and dynamic impact performance of hybrid cross-ply banana/glass fibre reinforced polypropylene composites

Natural fibres has been in demand as a replacement of synthetic fibres. However, natural fibres have disadvantages such as low mechanical properties compared to synthetic fibres, weak matrix to fibre adhesion and low thermal stability. Therefore, using natural fibres as a single reinforcement is inadequate to satisfy the technical needs of the composite. Hybridisation between natural and synthetic fibres can enhance the properties by taking the advantages of each of the individual fibres. This paper presents the hybridisation effect between banana and glass fibre. The low-velocity impact performance of hybrid cross-ply banana/glass fibre reinforced polypropylene composites were investigated and compared with quasi static indentation. Four types of stacking sequences composites were manufactured using hot compression moulding method, and the test was carried out according to American Society for Testing and Materials (ASTM) D6264 for quasi-static indentation and ASTM D7136 for low-velocity impact. The results revealed that the incorporation of glass fibre in banana fibre reinforced composite leads to higher energy absorption and improved the overall impact performance.

Simplified analytical approximations for scaled composite laminates under transverse loading

Delaminations caused by impact or indentation are a major cause of strength reduction in composite laminated structures. Since delaminations seldom occur in just one location through the thickness, the effect of multiple delaminations on the geometrical nonlinearity and response of scaled composite laminated plates subjected to a transverse concentrated load is studied here through analytical formulations. The scaling includes in-plane dimension scaling and sublaminate scaling based on a Reference plate with a stacking sequence of [45°/90°/0°/-45°]2S. The analytical approximation obtained under point loading quasi-static indentation is also suitable for studying large-mass low-velocity impact or for experiment and laminate design. The analytical approximations were compared with axisymmetric finite element model and static indentation tests conducted in a previous study. The novel achievement of this work is that it includes analytical expressions to predict the evolution of damage and load-displacement curves as a simpler alternative to the complex nonlinear finite element models.

Modern drilling technologies used for the making bored piles under the conditions of dense urban area

The parameters of drilling boreholes (including depth, diameter, angle of borehole inclination, cross-section) that are currently used for the making bored piles under the conditions of dense urban area, have been considered. The review about modern technologies of drilling boreholes used for making bored piles has been prepared. The updated classification of drilling technologies used for the making bored piles, which taking into account the nature of the removal of the destroyed rock and the movement of the drilling tool, the type of drilling tool, as well as the method of mounting the borehole walls, has been proposed. The classification, according to the nature of removal of the destroyed rock, distinguishes technologies providing or not providing the removal of destroyed rock. According to the nature of movement of the drilling tool, the rotary, shock and vibration technologies, as well as a static indentation technology, can be identified. According to the type of drilling tools, the classification divides methods into hollow drill stem with sacrificial drill bit and soil compactor and displacement tools with a starter auger section, augers, drilling buckets, core barrels, belling buckets, roller, impact and three-way bits, grabs. According to the methods of well casing, the technologies can be divided into the ones, allowing and not allowing the casing of well.

Damage mechanisms of polycrystalline aluminate magnesium spinel (PAMS) under different loading conditions of indentation and micro-cutting tests

This paper studies the damage mechanisms of polycrystalline aluminate magnesium (PAMS) under different loading conditions of indentation tests and micro-cutting with various rake angles of the cutting tools. A decreasing trend is confirmed in the hardness values with growing loadings. The observed hardness value approaches a plateau at about 1406–1679 HV. The tardive cracks, which break out spontaneously within a delayed period of time following the end of indentation, are for the first time observed in the indentation experiment of this paper. The tardive crack originates from a crack system containing a lateral subsurface crack with two median cracks on its both sides. These results imply that PAMS can store the unbalanced strain energy induced by the applied loading within the vicinity of the loaded volume which will be released in accordance with the intergranular crack-growing path extending to the surface. In addition, the linear plunge-cutting tests coin the effect of tool rake angle: the tool with a zero rake angle produces poor surface quality with sever surface damages whilst the tools with negative rake angles can improve the ductility of PAMS to a certain extent. However, negative rake angles are proved to be the root cause of median cracks and large spalling fractures. On the contrary, a positive rake angle tool can be applied to reduce the severity of surface damage and confine the damage patterns mainly as small spallings fractures. Besides the experimental study, finite element method (FEM) models are developed to reveal the underlying mechanism of the rake-angle effect on the micro-cutting process. The simulation results visualise the different stress distributions in the uncut areas and prove that a tool with positive rake angle can transfer the stress to the uncut chip layer whereby the damage probability to the machined surface is significantly reduced.

ГРАФИЧЕСКИЙ МЕТОД ВЫБОРА БУРОВЫХ ДОЛОТ

Актуальность исследования обусловлена необходимостью выбора перспективных буровых долот на стадии проектирования технологии бурения. Это направление является ресурсосберегающим, минимизирующим объем промысловых испытаний при поиске оптимальных технологических решений. Цель: разработать уточненную методику выбора буровых долот по статистическим данным о показателях механических свойств горных пород. Объекты: идентификация буровых долот различных фирм и их выбор в соответствии со статистическими характеристиками механических свойств горных пород. Эти вопросы слабо изучены и вызывают затруднения при проектировании режимов бурения скважин. Методы: графоаналитическое изучение соответствия типов буровых долот прочностным характеристикам горных пород, определяемым методом одноосного сжатия и методом статического вдавливания штампа с плоским основанием. Результаты. Для идентификации долот различных изготовителей Международная ассоциация буровых подрядчиков (МАБП) разработала единую классификацию в кодах МАБП. Для отечественной практики возникла дилемма: горные породы охарактеризованы твердостью горных пород по штампу и в категориях, а долота – прочностью горных пород при одноосном сжатии и в кодах МАБП. Предложен переход к показателю прочности горных пород, выраженному в кодах МАБП долота. Это обеспечивает единство характеристик как для долот, так и для горных пород. Соответственно предложены номограммы для выбора долот по статистическим величинам прочности горных пород в кодах МАБП, рассчитанных с надежностью 0,95. Показано, что можно аналогично выбирать долота и при представлении твердости горных пород в категориях. В случае лопастных алмазно-твердосплавных долот их выбор распадается на два этапа: выбор типа вооружения в соответствии с прочностью горной породы в кодах или твердостью в категориях и расчет числа лопастей долота, которое зависит как от прочностных характеристик горной породы, так и от диаметра долота. Для упрощения выбора долот предложено характеризовать буримость выделяемых интервалов бурения не словесно (мягкие, средние и т. д.), а их статистическими характеристиками в кодах МАБП или в категориях буримости с заданной вероятностью.

Effect of Experimental Variables on Nanomechanical Properties of PEK-C via AFM Indentation

Abstract In order to investigate the effects of the experimental variables of nanoindentation measurements on the nanomechanical properties of PEK-C, a wide range of indentation conditions, including peak force, loading velocity, and unloading velocity, were employed for PEK-C under different preparation conditions by the atomic force microscope based nanoindentation technique. The test results indicate that both the elastic modulus and hardness values decrease with the peak force increasing. The elastic modulus increases as the loading velocity increases. However, increasing unloading velocity leads to the decrease of the elastic modulus. The hardness exhibits a decrease with the loading velocity increasing and appears unloading velocity independent. What is more, the dispersion augments with the loading and unloading velocity increasing.

Qua si Static Indentation Behavior o f Nanoclay Chopped Carbon Fibres Composites

This paper presents the Quasi Static Indentation (QSI) behavior of the chopped carbon fibre composites with three different loadings of nanoclay. The composites, which are Carbon fibre (CF), 1wt% Nanoclay–Carbon Fibre (1NC-CF), 3wt% Nanoclay–Carbon Fibre (3NC-CF) and 5wt% Nanoclay–Carbon Fibre (5NC-CF) were prepared using hand lay-up method. The nanoclay was dispersed using a three roll milling machine. The 10wt% of chopped carbon fibres with 3-5 mm length were used in fabricating these composites. The QSI test was conducted using Universal Testing Machine according to the ASTM D6264. The damage section was examined using optical microscopy. The results show that the energy absorbed was increased with addition of nanoclay up to 81.42 %, 137.69 % and 202.95 % for 1NC-CF, 3NC-CF and 5NC-CF composites, respectively. It was concluded that the addition of the nanoclay enhanced the QSI of chopped carbon fibres composites.

Lateral cracks during sliding indentation on various optical materials

AbstractA series of static and sliding indentation (ie, scratching) was performed and characterized on a wide range of optical workpiece materials [single crystals of Al2O3 (sapphire), SiC, Y3Al5O12 (YAG), CaF2, and LiB3O5 (LBO); a SiO2–Al2O3–P2O5–Li2O glass ceramic (Zerodur); and glasses of SiO2:TiO2 (ULE), SiO2 (fused silica), and P2O5–Al2O3–K2O–BaO (Phosphate)] at various applied loads using various indenters (Vickers, 10 µm conical, and 200 µm conical). Despite having different load dependencies, the lateral crack depth formed during sliding indentation quantitatively scales with that formed during static indentation, explaining why static indentation has been historically effective in describing various grinding parameters. Depending on the indenter geometry, the amount of residual trench damage (plastic deformation and local fracturing) during sliding indentation was often enhanced by more than an order of magnitude compared with static indentation. A simple ploughing scratch model, which considers both tangential and normal stresses (where the tangential stress is amplified by relatively small tangential contact area), explains this enhancement and other observed trends. Accounting for the high correlation between residual trench depth and volumetric fracturing, the model is extended to estimate the amount of fracture damage as a function of the material properties of the workpiece, indenter geometry, and applied load. Such a model has utility in the design of optimized grinding processes, particularly the abrasive geometry. Finally, at higher loads (>1 N), lateral cracks were often observed to preferentially propagate in the forward scratching direction, as opposed to perpendicular to the scratch as typically observed. High‐speed imaging of the scratch process confirms that these cracks propagate ahead of the sliding indenter during the scratching event. Finite element stress analysis suggests the ploughing frictional forces increase the mode I tensile stresses at the leading edge of the sliding indenter explaining the direction of crack propagation of such cracks.

Investigating the Effects of Mechanical Stimulation on Retinal Ganglion Cell Spontaneous Spiking Activity.

Mechanical forces are increasingly recognized as major regulators of several physiological processes at both the molecular and cellular level; therefore, a deep understanding of the sensing of these forces and their conversion into electrical signals are essential for studying the mechanosensitive properties of soft biological tissues. To contribute to this field, we present a dual-purpose device able to mechanically stimulate retinal tissue and to record the spiking activity of retinal ganglion cells (RGCs). This new instrument relies on combining ferrule-top micro-indentation, which provides local measurements of viscoelasticity, with high-density multi-electrode array (HD-MEAs) to simultaneously record the spontaneous activity of the retina. In this paper, we introduce this instrument, describe its technical characteristics, and present a proof-of-concept experiment that shows how RGC spiking activity of explanted mice retinas respond to mechanical micro-stimulations of their photoreceptor layer. The data suggest that, under specific conditions of indentation, the retina perceive the mechanical stimulation as modulation of the visual input, besides the longer time-scale of activation, and the increase in spiking activity is not only localized under the indentation probe, but it propagates across the retinal tissue.

Theoretical prediction model for indentation of pipe-in-pipe structures

Pipe-in-pipe structures have been widely used in deepwater offshore oil and gas fields because of its excellent thermal insulation, good stability and outstanding resistance to thermal and external loads. Unfortunately, there is no theoretical prediction model for studying the indentation of pipe-in-pipe structures which is important in improving its design and optimization. In this paper, a theoretical model is proposed to predict the indentation of pipe-in-pipe structures by evaluating three stages of PIP indentation: the indentation of outer pipe only, the indentation of rigidly supported outer pipe and overhanging inner pipe, and the indentation of rigidly supported outer and inner pipes, which forms that describes the mechanical behavior of the inner and outer pipes of the PIP system. Finite element models of the lateral and normal sections of pipe-in-pipe are established and analyzed at each loading and indentation conditions of the inner and outer pipes. Parametric analysis of PIP properties is conducted to evaluate their effects on the nature of pipe-in-pipe indentation. The results of the comparative studies show that the proposed model has a better performance and provides a theoretical solution for design and analysis of pipe-in-pipe structures.

Comparative Evaluation of Quasi-Static Indentation Behaviour of Glass Fiber Reinforced (GFRP) and Carbon Fiber Reinforced (CFRP) Laminates

A comparative study of Quasi Static Indentation (QSI) conduct of Glass Fiber Reinforced Laminates (GFRP) and Carbon Fiber Reinforced Laminates (CFRP) of different thicknesses is made in this work. QSI tests are performed as per ASTM Standard D 7766M using custom – built Digital Flexural test equipment with dedicated fixture which provides constraint from all the four sides. A hemispherical Indentor of 12.5 mm diameter made from hardened steel is used to indent the specimens at a speed of 25 mm/minute. The damage area at different stages of QSI are assessed using ultrasonic ‘A’ scan and macroscopic inspection. The influences of thickness and type of laminate on the QSI parameters such as peak load at fracture, energy absorbed till fracture and maximum deflections are determined. It is found that the initial stiffness and the energy required for complete fracture is significantly more in case of CFRP as compared to GFRP laminate.Key words: QSI, GFRP, CFRP, Energy, Peak load, Initial Stiffness.

Indentation of expanded polystyrene foams with a ball

In this paper, a comprehensive study on the static and dynamic indentation of expanded polystyrene (EPS) foam blocks with a ball is carried out. An experimental study is carried out first to investigate the force response of EPS foams indented by a ball. The loading and unloading property and the strain rate effect of the EPS foams are also investigated. Numerical analyses are then performed by nonlinear finite element code LS-DYNA to simulate the tests. A theoretical model is proposed to predict the static and dynamic indentation responses of the EPS foams with a ball. Comparisons show that the theoretical predictions by the present model compare well with the experimental and numerical results.

Quasi-static indentation damage and residual compressive failure analysis of carbon fiber composites using acoustic emission and micro-computed tomography

In present research, the internal damage evolution and failure characteristics of carbon fiber woven composites under indentation and residual compressive loads were studied by using acoustic emission technology and X-ray micro-computed tomography. Real-time acoustic emission signals originating from internal damage of composites under applied loads were obtained and analyzed by the k-means clustering algorithm. Moreover, the internal damage characteristics were observed by the reconstructed three-dimensional model and the slice images of composite specimens. The results showed that the higher the indentation force reading, the more acoustic emission signals with high amplitude and frequency (over 300 kHz) are generated. Furthermore, the early acoustic emission signals with high-frequency were observed under residual compressive loads. It can be attributed to serious failures of fibers with the increase of static indentation loads. In addition, the internal damages such as delamination, debonding, crack and fiber breakage can be clearly characterized by micro-computed tomography and scanning electron microscopy observation. The complementary technology combing acoustic emission with micro-computed tomography can provide a better understanding of internal damages and evolution behaviors of the composites.

Nonwoven polyester interleaving for toughness enhancement in composites

Various researchers have developed techniques to control delamination in laminated structures. One of these techniques is “interleaving,” adding high toughness material to key interfaces in a laminate. This paper studies using polyester veil as a low-cost interleaf alternative to other materials and focuses on a nonwoven, polyester spunbond material. Two different interleaf thicknesses, 0.18 mm and 0.74 mm, are primarily used. In addition, fine 4 g/m2 polyester was also compared. Carbon/epoxy composites are manufactured using 2 × 2 Twill 24″–12k carbon fibers embedded in an epoxy resin, with polyester interleaves at key interfaces. Specimens are fabricated using wet hand layup and cured at room temperature in a vacuum bag. Mode I fracture toughness is measured using the double cantilever beam test and Mode II fracture toughness is examined using the end-notched flexure test. Further evaluation is made using static indentation and full penetration impact testing. Toughness is compared, and the resulting fracture surfaces are investigated. Significant improvement is seen in Mode I testing. Up to a factor of 4 increase in propagation energy per unit area resulted from the inclusion of the interleaf material. Smaller improvements were observed in Mode II, with the best cases showing an increase in propagation energy to maximum load by about a factor of 2 compared with control cases. The polyester interleaf significantly influences the fracture morphology observed in static indentation and full penetration tests.

Remaining strength assessment of dented pipe based on depth and strain based criteria

There are currently two methods which are used in feasibility operation of dented pipeline systems, namely depth based and strain based. In this research, both methods will be compared to determine conservatism degree of each method and as a guideline and considerations in the integrity assessment of pipeline system. The finite element method with including nonlinearities of material properties and dimension will be used as a tool in the analysis. Static indentation was held with using half ball indenter. Variations of applied load are 600 N, 1000 N, 1500 N, 2000 N, and 2500 N. The results of indentation are dent depth ratio (d/D) with value 1,93 %, 3,78 %, 5,53 %, 7,08 %, 10,63 %, and plastic strain with value 4,24 %, 5,87 %, 8,36 %, 11,43 %, and 12,93 %, respectively. Based on the Code, depth based criteria use d/D<6 % and strain (ɛ) < 6 % as an acceptance criteria. Based on this research, it can be concluded that strain based method is more conservative rather than depth based method. Then, five model of defected pipe will be simulated in the condition of operation pressure applied to the pipe. Operation pressure was varied with (P/Py) 0.2, 0.4, 0.6, 0.8, and 1. The results show that depth of dent will decrease with variation of strain value.