Static Indentation Tests Research Articles

Effect of composition and annealing temperature on the mechanical properties of a vitrified waste

The microhardness and indentation fracture toughness of a vitrified industrial waste, in the form of ash, were characterized by the method of static indentation test. These properties were investigated as a function of composition and thermal treatment conditions. To further understand the influence of the constitutive oxides, additional measurements were made in a series of synthetic products, where a mixture of iron and lead oxides was used as a substitute for the ash. The underlying deformation mechanisms controlling the mechanical properties of such complex systems as determined by static indentation tests are discussed. It was found that plasticity, in the amorphous products, is mainly governed from the silica content, even in the cases where silica is not found in sufficient quantity in order to build an extended three-dimensional vitreous network. On the other hand, the morphology of the separated crystalline phases is the dominant factor affecting plasticity in the glass-ceramic products.

Deforamtion and Fracture Behavior of Zr-Based Bulk Amorphous Metal Under Quasi-Static Compression

The deformation and fracture behaviors of a bulk amorphous metal, Zr-based one ( Zr 41.2 Ti 13.8 CU 12.5 Ni 10 Be 22.5: Vitreloy), were investigated over a strain rate range (7 × 10-4~4 s -1). The uniaxial compression test and the indentation test using 3mm-diameter WC balls were carried out under the quasi-static loading condition. As a test result, at the uniaxial compression state, the fracture strength of the material was ~1,700MPa and the elastic strain limit was about 2%. The fracture strength showed a strain rate independent behavior up to 4 s-1. Using indentation tests, the plastic deformation behavior of the Zr-based BAM up to a large strain value of 15% could be achieved, even though it was the deformation under locally constrained condition. The Meyer hardness of the Zr-based BAM measured by static indentation tests was about 5 GPa and it revealed negligible strain hardening behavior. At indented sites, the plastic indentation occurred forming a crater and well-developed multiple shear bands were generated around it along the direction of 45° when the indentation load exceeded 7kN. With increasing indentation load, shear bands became dense. The fracture surface of the specimen after uniaxial compressive tests showed vein-like pattern, typical morphology of many BAMs.

Static Load Dispersion Function of Solid-Air Composites (Effect by the distribution of Internal Hydrostatic Pressures)

In order to make a new movement of the composite material design, the purpose of the present study is applying the solid-air composites derived from the load dispersion structure of living bones to investigate the static load dispersion function shown by the mechanical behavior of those constitutive elements. Internal hydrostatic pressures were controlled by making a hole in cell walls of the honeycomb core. Static indentation tests were carried out to examine the load dispersion effect. In-plane cell's deformations and stress distributions at the bottom surface of the specimens were measured optically. Experimental results illustrated that the distribution of the internal hydrostatic pressures greatly influenced on the deformation condition of the solid part. Consequently, it is considered that controlling the internal hydrostatic pressures is an effective design parameter of the load dispersion function.

A parametric study of implantation-induced variations on the mechanicalproperties of epitaxial GaN

Doping of GaN through ion implantation permits improved control of the dopantprofile and dose, while it also modifies the film’s mechanical properties suchas microhardness. We discuss the effect of Si+- and Mg+-ion implantationon the mechanical properties of GaN films grown by electron cyclotronresonance plasma-assisted molecular beam epitaxy on sapphire substrates.The changes of the mechanical properties are studied using the staticindentation method and they are discussed in conjunction with results fromnear-edge x-ray absorption fine-structure spectroscopy. Transmission electronmicroscopy is used for the microstructural characterization of selectedimplanted specimens. The static indentation test method was applied utilizingVickers and Knoop diamond indenters. The microhardness results areabsolved from the influence of the substrate through the implementation ofa well-established deconvolution method. The elastoplastic response ofthe films are compared and discussed on the basis of the proportionalspecimen resistance model and the form of the indentation size effect curves.

섬유의 적층 각도에 따른 섬유 금속 적층판의 압입 손상 거동

In this research, the effects of fiber stacking sequence on damage behaviors of FML(Fiber Metal Laminates) subject to indentation loading. SOP (Singly Oriented Ply) FML and angle ply FML were fabricated to study fiber orientation effects and angle ply effects. FML were fabricated by using 1050 aluminum laminate and carbon/epoxy prepreg. To increase adhesive bonding strength, AI laminate was etched using FPL methods. The static indentation test were conducted by using UTM under the 2side clamped conditions. During the tests, load and displacement curve and crack initiation and propagation behaviors were investigated. As fiber oricntation angle increases, thc crack initiation load of SOP FML increases because the stiffness induced by fiber orientation is increased. The penctration load of SOP FML is influenced by the deformation tendency and boundary conditions. However, the macro-crack of angle ply FML was initiated by fiber brcakage of lower ply because angle plies in Angle ply FML prevents the crack growth and consolidation. Thc Angle ply FML has a critical cross-anglc which prevent crack growth and consolidation. Damage behavior of Angle ply FML is changed around the critical cross-angle.

Delamination monitoring of graphite/epoxy laminated composite plate of electric resistance change method

The present paper employs the electric resistance change method for monitoring of location and size of a delamination crack of graphite/epoxy composite laminates. The method is applied to a plate-type specimen with an embedded delamination of cross-ply and quasi-isotropic laminates. Ten electrodes made from copper foil are mounted on the specimen top surfaces. An embedded delamination crack is created by a static indentation test, and the electric resistance changes are measured using a conventional strain gage amplifier. Response surfaces are adopted as a tool for solving inverse problems to estimate location and size of delamination crack from the measured electric resistance changes of all segments between electrodes. As a result, the present method successfully provides estimations of location and size of the embedded delamination for graphite/epoxy laminated composites.

Development of solid–fluid biomimetic composites: Load dispersion effect of controlled hydrostatic pressure

The purpose of this research project is to apply biomimetic-designed composites to artificial structures. The natural bone is an optimum-designed structural system to support the living body. So, it is very useful in developing original optimum designs of the composite materials to study composite structures of the bone. Looking at the bio-joint mechanism, the solid–fluid composite structure of the cancellous bone has likely important effect in the load transmission. In this study, the solid–fluid composite model of the cancellous bone was made by using honeycomb structure. Static-indentation tests were carried out, and in-plane deformation conditions of the specimens were measured quantitatively. At first, the load dispersion effect of two kinds of fluid was examined by using small cell size Al honeycombs. Air and glycerine were sealed in each hexagonal cell of the specimens with thin films, respectively. But the film adhesion did not affect the deformation of honeycomb structures. Even the hydrostatic pressure of air greatly affects the in-plane deformation condition of the solid phase. Next, the load dispersion effect of the controlled hydrostatic pressure was examined by using large cell size Al honeycombs. The propagation of air hydrostatic pressure in the specimens was controlled by making a small hole in the specific cell walls of the honeycomb structure. Consequently, as for the solid–fluid composite models, the possibility of the optimum control of the compressive load dispersion was expected.

Surface and subsurface damages and magnetic recording pattern degradation induced by indentation and scratching

Magnetic recording pattern degradation due to head–disk impact and scratching are simulated by static indentation and scratch testing, respectively, on a pre-recorded thin film magnetic recording disk. Different magnitude of controlled stresses were used to induce stress and physical damage to the magnetic recording disk resulting in erasure and distortion of the magnetic recording pattern. Both nanoindentation and scratching resulted in the elastic–plastic deformation of the multilayer coating of the magnetic recording disk but in different relative magnitude and types of in-plane stresses (which are effective in causing magnetization changes). For residual indentation and scratch depths of the order of the magnetic disk coating thickness, magnetization changes in the recording pattern were observed even though the protective carbon overcoat was not damaged. Large magnetic pattern distortion and erasure results where cracks and pileups, and delamination and buckling damages were observed for deeper indentation marks and scratch grooves, respectively.

Characterisation of impact response of metallic foam/ceramic laminates

The impact response of laminated composites consisting of alternate layers of Al alloy foam and Al2O3 was studied experimentally in low and intermediate velocity regimes. Low velocity impacts (1.2–2.8 m s-1) were conducted using an instrumented falling weight apparatus and were compared with static indentation tests (0.2×10-4 m s-1). Intermediate velocity impacts were carried out by means of both Hopkinson bar (60 m s -1)and gas gun (200 m s-1) tests. Post­impact damage was assessed using X-ray radiography and microscopy. It was found that there is good correlation between low velocity impact and quasi­static responses. In both cases, penetration of the layered targets resulted in the formation of a distinctive plug. Increasing impact velocity (intermediate velocity range) switched the penetration mode from plugging to fragmentation, giving rise to an increase in the absorbed energy. In this range, impacts led to localisation of damage in the region under the projectile. Furthermore, a comparison has been made between the penetration response of foam laminates and dense metal laminates of equivalent areal density. Preliminary results suggest that the dense metal laminates are superseded by the foam laminates on an energy absorption basis.

Static indentation and impact behaviour of reformed bamboo/aluminium laminated composites

A series of static indentation and impact tests at different speeds were carried out to study the deformation behaviour and damage resistance of reformed bamboo/aluminium laminate composites. The load–displacement records were analysed, and the C-scan images as well as cross-sectional fractographs were examined to identify the failure mechanisms at different loading/boundary conditions. It was shown that the laminates deformed and failed in a totally different manner under different boundary conditions: the resistance to deformation and damage was much higher for the fully supported boundary than for the condition with clamped edges and an open window. Meanwhile, the mechanical response was little affected by loading speeds up to 3.5 m/s, and by laminate configuration, i.e. laminates with unidirectional or cross-ply bamboo layers.

A study of pre-stress effect on static and dynamic contact failure of brittle materials

Layered plates consisting of brittle glass and ductile aluminum layers were fabricated using room temperature and elevated temperature curing adhesives. Significant thermal residual stresses were induced in the layered plate bonded at an elevated temperature. Static indentation and dynamic impact tests were performed. The results indicate that thermal residual stresses can delay the onset of contact failure in the glass. However, the benefit of thermal residual stresses in protecting the structure from fracture failure seems to diminish once the projectile achieves substantial penetration into the layered target. The conoid cracking in the glass layer produced by static indentation was modeled using linear elastic fracture mechanics with very good result.

Impact perforation of thin stiffened CFRP panels

Static indentation and dropweight impact tests have been performed on thin CFRP panels stiffened with three T-blade stiffeners and comparisons made with similar tests on plain panels. The impact perforation threshold energy may be estimated from the work done by the indentor during a static indentation test for both plain and stiffened panels. For impacts conducted in-line with the stiffener the perforation energy is significantly increased and the maximum damage levels occur at higher energies than for other panel loading conditions.

Determination of resudual stress fields beneath a Vickers indentation using photoelasticity

Static Vickers indentation tests were performed on Homalite specimens with an intent to obtain the residual stress distribution beneath the indentation. The indented specimens were placed in a circular polariscope to view the fringe patterns corresponding to the induced residual stress. Similitude analysis was later employed to identify the functional relationship between the various parameters related to an indentation test. The analysis resulted in a unified relationship that can assist in the determination of residual stress in nontransparent materials subjected to similar geometric and loading conditions. The shear stress contours provided here can also be used as guidelines to verify constitutive models under complex three-dimensional loads.

Solid-Fluid Biomimetic Composites by Considering Load Dispersion Mechanism of Cancellous Bone Structure. Consideration of Honeycomb Structure.

The purpose of this research is to apply biomimetic designed composites to artificial structures. Looking at the bio-joint mechanism, the solid-fluid composite structure of the cancellous bone is likely to play a great important role in the load transmission. So, the solid-fluid composite model equal to the cancellous bone was made by using honeycomb structure. Static indentation testing was carried out, and in-plane deformation conditions of the solid-fluid composite specimens were measured quantitatively. Experimental results illustrated that the hydrostatic pressure of the fluid phase greatly influenced on the in-plane deformation condition of the solid phase. Consequently, as for the solid-fluid composite models, the compressive load dispersion by the solid-fluid phase interaction was expected.

Low velocity impact damage characteristics of Z-fiber reinforced sandwich panels — an experimental study

Experimental results related to the initiation of damage in Z-fiber truss-reinforced sandwich panels are presented. Two different orientations of pin angles are considered. A pendulum-type impactor is used to impart very low levels of impact energy. Threshold energy levels at which the observable damage initiation occurs are determined. Nondestructive evaluation studies conducted prior to the impact are compared with the post-impact status of the panels for assessing the type and magnitude of the damage. These studies include ultrasonic inspection, microscopic inspection and acoustic emission tests. Damage is also evaluated by carrying out vibration tests before and after impact. Static indentation tests are carried out to compare with low velocity impact tests. Effects specific to the impact phenomena are studied by comparing the load displacement characteristics. Compression after impact characteristics are also evaluated.

Directional indentation of transcrystalline polypropylene

The directional Young's modulus of transcrystalline isotactic polypropylene grown from the surface of high modulus carbon fibers has been measured by two types of Knoop microindentation experiments. First, static indentation tests were performed and a new data reduction procedure was used to translate the Knoop hardness data into modulus values. The technique assumes that the extent of elastic recovery of a Knoop indent is linearly related to the modulus-to-hardness ratio. The Knoop tip is sensitive to material anisotropy, which allows us to generate data for the different lamellar directions. The hardness and Young's modulus of the transcrystalline layer are found to be higher by up to 30% when the longer diagonal of the probing Knoop tip is perpendicular to the transcrystalline growth direction. Second, continuous indentation tests are performed and a different data reduction technique is used, which leads to similar results. The microindentation approach used here is found to be particularly advantageous for the assessment of Young's modulus of small-scale polymeric regions or when only small polymeric specimens are available.

Directional indentation of transcrystalline polypropylene

The directional Young's modulus of transcrystalline isotactic polypropylene grown from the surface of high modulus carbon fibers has been measured by two types of Knoop microindentation experiments. First, static indentation tests were performed and a new data reduction procedure was used to translate the Knoop hardness data into modulus values. The technique assumes that the extent of elastic recovery of a Knoop indent is linearly related to the modulus-to-hardness ratio. The Knoop tip is sensitive to material anisotropy, which allows us to generate data for the different lamellar directions. The hardness and Young's modulus of the transcrystalline layer are found to be higher by up to 30% when the longer diagonal of the probing Knoop tip is perpendicular to the transcrystalline growth direction. Second, continuous indentation tests are performed and a different data reduction technique is used, which leads to similar results. The microindentation approach used here is found to be particularly advantageous for the assessment of Young's modulus of small-scale polymeric regions or when only small polymeric specimens are available.

Damage in gamma titanium aluminides due to small particle impacts

Initiation of cracking due to small particle impacts on low ductility intermetallics is investigated experimentally and theoretically. The gamma titanium aluminide alloys of interest which are being considered for elevated temperature structural applications in aircraft engines exhibit tensile ductilities on the order of 1–2%. Cracking due to any source, including small particle impacts, is of concern given the rapid growth of cracks in fatigue. This investigation focuses on a model geometry which reproduces the rear face cracking that is induced by a small particle impinging on an air foil leading edge. Small steel spheres are projected onto thin plates at velocities ranging from 76 to 305 m\\s ; cracking is thereby induced on the rear surface of the plates. Through finite element analyses of the dynamic impact event and some analytical estimates, we examine the hypothesis that crack initiation due to small particle impacts can be correlated with material ductility and with the severity and spatial extent of the straining during the impact event. In addition, with the use of static indentation tests in which similar strain distributions are present, some insight is gained into the difference in ductility between high and low strain rates. © 1998 Elsevier Science Ltd. All rights reserved.

Low-velocity impact damage initiation in graphite/epoxy/Nomex honeycomb-sandwich plates

Low-velocity impact and static indentation tests on sandwich plates composed of 4- to 48-ply graphite/epoxy cross-ply laminate facesheets and Nomex honeycomb cores have been performed to characterize damage initiation as a function of facesheet thickness and loading rate. Force histories during low-velocity impact are measured by using an instrumented impactor and integrated to produce energy histories. Energy histories are shown to reveal damage initiation. Static indentation tests show damage that is similar to that produced by low-velocity impact. The force at which damage initiates is shown to be lower for static tests than for low-velocity impact tests, and differences between equilibrium curves for the two types of loading are discussed. The difference between static and low-velocity impact tests is greater for plates with thicker facesheets. This may indicate a limitation of the applicability of the common assumption that low-velocity impact is a quasi-steady process.

Solid-Fluid Biomimetic Composites by Considering Load Dispersion Mechanism of Cancellous Bone Structure. 1st Report. Consideration of Honeycomb Structure.

The purpose of this research is to apply biomimetic designed composites to artificial structures. Looking at the bio-joint mechanism, the solid fluid composite structure of the cancellous bone is likely to play a great important role in the load transmission. So, the solid-fluid composite model equal to the cancellous bone was made by using honeycomb structure. Static indentation tests were carried out, and in-plane deformation conditions of the solid-fluid composite specimens were measured quantitatively. Experimental results illustrated that the hydrostatic pressure of the fluid phase greatly influenced on the in-plane deformation condition of the solid phase. Consequently, as for the solid-fluid composite models, the compressive load dispersion by the solid-fluid phase interaction was expected.