Tungsten Carbide Spheres Research Articles

Observations and Characterization of Damage in Diamond Coatings Due to Impact Loading

This paper describes a single‐impact study of diamond coatings on tungsten substrates. A gas blast erosion test facility was used to impact 2.38‐mm‐diameter tungsten carbide spheres onto diamond‐coated tungsten at a velocity of 37 m/s. The results show that the impacts result in the formation of ring cracks, whose maximum diameters do not show any significant dependence on the coating thickness. The ring cracks do not agree with the contact diameters as predicted using Hertz' dynamic impact theory, the ring crack diameters being significantly larger than those predicted by the theory. These discrepancies can be attributed to a modified stress field generated by friction between the sphere and the target, as well as plastic deformation of the spheres during impact. A closer agreement with the Hertz theory was seen in the case of subsurface damage: significant delamination was observed adjacent to impact sites on coatings where the depth of maximum shear stress was close to the coating–substrate interface. This finding needs to be borne in mind when designing coated systems for use in erosive environments or applications where impact resistance is required.

Effects of density ratio and diameter ratio on critical incident angles of projectiles impacting granular media

The dynamic behavior of projectiles upon impact with granular media was recorded using two high-speed video cameras for capturing different angles. We used steel, brass, tungsten carbide spheres, and alumina ceramic spheres with diameters in the range of 6-20 mm as the projectiles and poly- styrene beads (6 mm in diameter) and glass beads (1.7 mm in diameter) as the granular media. Upon impact, the projec- tiles penetrated the media, rebounded from the media, or were deflected such that their resulting motion was in a horizontal direction. Post-impact motion of the projectiles depended on the impact angles of the projectiles, the density ratio (bulk density/projectile density), and the diameter ratio (granular diameter/projectile diameter) and not on the impact veloc- ity. The post-impact motion of the projectiles did not fol- low a clear trend in terms of the transient angle; instead, we observed the existence of a transient region. On the basis of the area of the transient regions, an empirical equation was derived for determining the critical angle of projectiles (the angle at which they can penetrate the granular media) as a function of the density ratio and the diameter ratio.

Contact Damage of Curved Multi-Layered Ceramics: Prepared by Slip Casting Technique

Contact damage of curved multi-layered systems, consisting of a brittle zirconia (3Y-TZP)/Alumina (Al2O3) coating – prepared by slip casting – on a compliant polymeric substrate from indentation by a hard tungsten carbide sphere is investigated. The essence of this study is to compare the structural performance of layered ceramics, and monolithic ceramic in the brittle coating and compliant substrate of dental crown-like systems. The specimens are loaded at the axis of symmetry. The failure evolution to initiate cracking and final failure patterns in curved multi-layered specimens are compared to those of the single layer specimens of the same thickness and the same study are conducted again with the flat specimens. The onset of fracture is observed in situ using a video camera. It is demonstrated that in all specimens, cone cracking occurs prior to radial cracking, with the latter being defined as the primary mode of catastrophic failure. The multi-layered ZTA (Zirconia Toughened Alumina) specimens prepared by slip casting possessed a distinct final failure pattern in comparison with a single layer specimen. The results of this study provide useful guidelines for building brittle multi-layered coating systems with the functionally graded feature, and complex shapes with geometrical uniformity.

Calibration methods for two scientific multibeam systems

Abstract Ona, E., Mazauric, V., and Andersen, L. N. 2009. Calibration methods for two scientific multibeam systems. – ICES Journal of Marine Science, 66: 1326–1334. The new Simrad scientific multibeam systems, the MS70 sonar and the ME70 echosounder, each transmit over many electronically formed beams with centre frequencies spanning from 70 to 120 kHz. Calibrations of these systems are therefore more complex than for conventional split-beam echosounder systems. Two large tungsten-carbide spheres (75 and 84 mm diameter) were designed and manufactured to facilitate accurate field calibrations over the entire operational bandwidth. These are heavy and therefore stable when suspended beneath a ship, and have target strengths much larger than those of biological targets potentially within the measurement volume. This paper presents procedures for calibrating each system in the field and the results from two such experiments. Detailed inspections of the results for individual beams indicate that minor adjustments in the described procedures might further improve the reported calibration accuracy.

Fracture Modes in Curved Brittle Layers Subject to Concentrated Cyclic Loading in Liquid Environments.

Damage response of brittle curved structures subject to cyclic Hertzian indentation was investigated. Specimens were fabricated by bisecting cylindrical quartz glass hollow tubes. The resulting hemi-cylindrical glass shells were bonded internally and at the edges to polymeric supporting structures and loaded axially in water on the outer circumference with a spherical tungsten carbide indenter. Critical loads and number of cycles to initiate and propagate near-contact cone cracks and far-field flexure radial cracks to failure were recorded. Flat quartz glass plates on polymer substrates were tested as a control group. Our findings showed that cone cracks form at lower loads, and can propagate through the quartz layer to the quartz/polymer interface at lower number of cycles, in the curved specimens relative to their flat counterparts. Flexural radial cracks require a higher load to initiate in the curved specimens relative to flat structures. These radial cracks can propagate rapidly to the margins, the flat edges of the bisecting plane, under cyclic loading at relatively low loads, owing to mechanical fatigue and a greater spatial range of tensile stresses in curved structures.

2次元マルチビームエコー積分による魚量推定

The two-dimensional multibeam echo integration (2DMBEI) method, which provides the user with the target strength of a fish school, was derived analytically based on the theory of three-dimensional multibeam echo integration. It was developed to establish a reliable and practical methodology of fish abundance assessment using scanning sonar for fishery use. The 2DMBEI method was implemented in the data analyzing software of a quantitative scanning sonar system. Furthermore, a sea experiment using tungsten carbide spheres simulating a fish school was conducted to validate the 2DMBEI method.

Measuring the target strength spectra of fish using dolphin-like short broadband sonar signals

Dolphins identify their prey using broadband sonar signals. The broadband spectrum of the target strength (TS) of fish is believed to be a key factor in target discrimination. In this study, the TS spectrum was measured using sonar signals generated by two different dolphin species: finless porpoise and bottlenose dolphin. First, the broadband form functions of a tungsten carbide sphere and a copper sphere were measured in a water tank, and a close agreement between measurements and theoretical values was confirmed. Second, the TS spectra of anesthetized fish from three species were measured in a water tank. Although the results showed characteristics similar to previous measurements, they varied among species, individuals, and tilt angles. Third, the TS spectra of live fish suspended and tethered by nylon monofilament lines were measured at sea. The dolphin-like sonar signals were effective in obtaining the broadband TS spectra of the fish. Cross-correlation processing of the echo from a tungsten carbide sphere showed a further advantage of using the dolphin-like sonar signals: the signal-to-noise ratio increased by more than 10 dB. The variation of TS spectra with fish behavior provides useful information for target identification.

Computational modeling of tungsten carbide sphere impact and penetration into high-strength-low-alloy (HSLA)-100 steel targets

Computational modeling of tungsten carbide sphere impact and penetration into high-strength-low-alloy (HSLA)-100 steel targets

Relationships between multiaxial stress states and internal fracture patterns in sphere-impacted silicon carbide

Internal fracture patterns developed in silicon carbide cylindrical targets as a result of dynamic indentation (63–500 m/s) by tungsten carbide spheres are defined. Microscopy of recovered and sectioned targets delineate into three regions, each associated with distinct cracking modes, i.e., shallow cone macrocracking at and near the impact surface, steep interior cone macrocracks that radiate into the target from the impact region and local grain-scale microcracking directly underneath the impact region. The observed fracture patterns are found to maintain a noticeable degree of self-similarity upto the impact velocity of 500 m/s. Linear elastic analysis of the full (surface and interior) stress field developed under static (Hertz) contact loading delineate the target into four regions, based on the number of principal stresses that are tensile (none, 1, 2 or all 3). A strong correlation is found between the principal stress conditions within each region and the forms of cracking, their locations and orientations present therein. This correlation has a number of implications, including non-interaction of crack systems, which are discussed. Illustrative linear elastic fracture mechanics analyses are performed for three regions, and calculated and observed macrocrack lengths are found to be in reasonable agreement.

Characterization of Ballistic Impact Damage in Wired Glass

The ballistic impact behavior of wired glass has been studied. Three types of commercially available samples, with thin and thick wire mesh, were impacted with steel, glass, and tungsten carbide spheres of various sizes using a gas gun. Impact energies varied from 0.5 to 40 J. A system of cracks was found to develop that comprised primarily a major cone crack. At higher energies, additional radial and lateral cracking developed along with increased damage to the front face of the sample. The extent of damage was assessed in terms of basal cone crack area, number of cracks, mass loss, and fracture load of impacted samples. It was found that damage, at a given impact energy, increased with increasing projectile diameter. Moreover, 10 mm diameter glass spheres caused more damage than smaller (3–4.74 mm diameter) steel spheres. No significant differences were observed with regard to the ballistic behavior of the thin‐ and thick‐wired glass types.

Validation of multi-frequency inversion method by using dummy scatterers of zooplankton

High- and multi-frequency acoustic measurement systems and the multi-frequency inversion (MFI) method have been used to measure spatial distributions and abundances of zooplankton by size. In this study, the calibration method for high- and multi-frequency systems was developed and the validation of MFI method was carried out by scatterer measurement. The standard sphere calibration method that has not been applied to such high- and multi-frequencies was applied to calibrate our high- and multi-frequency system, TAPS-6 (Tracor Acoustic Profiling System, BAE Systems). An optimum size of standard sphere of tungsten carbide of 1 mm radius was derived to have a small target strength variation for the six frequencies of TAPS-6, and the practicability and precision of the standard sphere calibration method was confirmed for those frequencies. A school or cluster of dummy scatterers of zooplankton with small tungsten carbide spheres were designed to validate the MFI method, and volume back-scattering strength values were measured by the multifrequency system. By comparing the result of the inversion with their real composition, the features of the MFI method could be validated and examined.

Measurements of target strength spectra of metal spheres and fish by using broadband sonar signals of dolphin

Dolphins identify prey by using their broadband sonar signals. Considering that the spectrum of fish target strength (TS) leads to identification of objects, we measured the spectrum using dolphin’s sonar signals with a broadband system. The TS spectrum is obtained by dividing the echo spectrum by the incident spectrum while setting the projector and hydrophone face to face. First, we measured the broadband form function of a tungsten carbide and copper sphere in a water tank and confirmed good agreements with theoretical value. Second, we measured the spectra of TS of three species of anaesthetized fish in a water tank. Although the spectra showed nearly similar tendencies of past measurements, they changed according to the species, the individual, and the tilt angle. Third, we measured TS spectra of fish suspended by nylon monofilament line in the open sea in semi-in-situ. We tried to remove the directivity of transducers by a tungsten carbide sphere suspended near the fish. The change of the TS spectra should be important information for the fish identification.

Standard-target calibration of active sonars used to quantify aquatic organisms

The span of sonars being calibrated by the standard-target method continues to grow. In this retrospective of the past 25 years, the essence of the method is reviewed for both narrow-band and broadband systems. Applications to scientific echo sounders with operating frequencies from 18 kHz to 3.2 MHz are summarized. Applications to multibeam sonars that provide the water-column signal, with frequencies of 90, 200, 240, and 400 kHz, are also summarized. A planned application to a parametric sonar, with primary frequencies in the range 15–21 kHz and difference-frequency band 0.5–6 kHz, is described. The method is applicable to ordinary midfrequency sonars. In each example, particular standard targets are specified. Diameters vary from 10 mm for a sphere of tungsten carbide with 6% cobalt binder for use at low megahertz frequencies, to 60 mm for a sphere of electrolytic-grade copper for use at 38 kHz, to 280 mm for a sphere of aluminum alloy for use at low-kilohertz frequencies.

Microstructure of alumina reinforced with tungsten carbide

Carbides and nitrides reinforced alumina based ceramic composites are generally accepted as a competitive technological alternative to cemented carbide (WC-Co). The aim of this work was to investigate the effect of dispersed tungsten carbide (WC) on the microstructure and mechanical properties of alumina (Al2O3). Micron size alumina and tungsten carbide powders were mixed in a ball mill and uniaxially pressed at 1600°C under 20 MPa in an inert atmosphere. The hardness of WC reinforced alumina was 19 GPa and fracture toughness attained up to 7 MPa m1/2. It was demonstrated by TEM analysis that coarse, micrometersized tungsten carbide grains were located at grain boundaries of the alumina matrix grains. Additionally, sub-micrometer tungsten carbide spheres were found inside the alumina particles. Crack deflection triggered by the tungsten carbide at the grain boundaries of the alumina matrix is supposed to increase fracture toughness whereas the presence of intergranular and intragranular hard tungsten carbide particles are responsible for the increase of the hardness values of the investigated composite materials.

Blast phenomena associated with high-speed impact

An experimental, analytical, and numerical investigation was conducted in order to measure air pressure at the target surface near the point of normal impact into semi-infinite rolled homogeneous armor (RHA) of a high-speed, 10 mm diameter tungsten carbide sphere. Impact speeds varied from 0.9 to 3.8 km/s. Numerical simulations of the impact were conducted in which the crater lip and ejecta motion were successfully coupled with the surrounding air. An analytical model of the air blast field resulting from the impact has been developed employing the blast generated by a small explosive charge initiated at the time and point of impact. This is a one-dimensional solution in which all characteristics of the blast field are a function only of the radius from the charge center and the energy released by the charge. Thus, a single empirically derived parameter—the equivalent explosive charge energy—completely defines the blast field. For each test, this parameter was obtained from a least squares fit to the peak pressures measured as a function of distance from the impact (explosion) center. The model predicts the data well at all test speeds. The tests, analytical modeling, and numerical simulations resulted in the following conclusions: The air blast field contains about 0.7% of the kinetic energy of the impacting projectile and results from three sources: (1) the air entrained by the projectile which impinges upon the target plate; (2) the air accelerated by the radially expanding crater lip; and (3) the air entrained by the impact induced ejecta.

A comparative study on cyclic and static fatigue of dental ceramic by means of Hertzian's contact

To compare the difference in strength degradation and morphology damage of brittle dental ceramic after static load and cyclic fatigue. Hertzian's contact technique with a tungsten carbide sphere was used to investigate the response of feldspathic dental porcelain to static load and cyclic fatigue. All specimens were subjected to static or cyclic loading in moist environment. Furthermore the surviving strength of specimens was examined by the three-point test and the morphology damage was observed. Statistical analyses were performed with ANOVA and a P-value less than 0.05 was considered to be significant. Outer cone crack and associated strength degradation simultaneously occurred both after the first cyclic loading and static loading. Up to 1,000 cycles, the specimens showed inner cone cracks and strength degradation was aggravated. No significant difference in the strength degradation among all static loading specimens and no inner cone cracks occurred in static loading specimens. Both static and cyclic fatigue influence dental ceramic strength, but cyclic fatigue is more deleterious.

Competing Fracture Modes in Brittle Materials Subject to Concentrated Cyclic Loading in Liquid Environments: Monoliths

The competition between fracture modes in monolithic brittle materials loaded in cyclic contact in aqueous environments with curved indenters is examined. Three main modes are identified: conventional outer cone cracks, which form outside the maximum contact; inner cone cracks, which form within the contact; and median–radial cracking, which form below the contact. Relations describing short-crack initiation and long-crack propagation stages as a function of number of cycles, based on slow crack growth within the Hertzian field, are presented. Superposed mechanical driving forces—hydraulic pumping in the case of inner cone cracks and quasiplasticity in the case of median–radials—are recognized as critically important modifying elements in the initial and intermediate crack growth. Ultimately, at large numbers of cycles, the cracks enter the far field and tend asymptotically to a simple, common relation for center-loaded pennylike configurations driven by slow crack growth. Crack growth data illustrating each mode are obtained for thick soda-lime glass plates indented with tungsten carbide spheres in cyclic loading in water, for a range of maximum contact loads and sphere radii. Generally in the glass, outer cone cracks form first but are subsequently outgrown in depth as cycling proceeds by inner cones and, especially, radial cracks. The latter two crack types are considered especially dangerous in biomechanical applications (dental crowns, hip replacements) where ceramic layers of finite thickness are used as load-bearing components. The roles of test variables (contact load, sphere radius) and material properties (hardness, modulus, toughness) in determining the relative importance of each fracture mode are discussed.

The significance of high-order resonances of spherical bubbles to the acoustic response of fish with swimbladders

The high-order resonant response of spherical gas bubbles in seawater, when insonified by an acoustic pulse of 12 cycles of 38 kHz, used for target strength measurements, shows substantial variation in shape with only small changes in bubble radius. In contrast, the amplitude response of a gas bubble near its fundamental resonance changes predominantly in magnitude as the radius changes. The fundamental response is very similar to that of a more rigid target such as a tungsten carbide sphere. It might initially be thought that the high-order resonant response of spherical gas bubbles in seawater would have little relevance to the response of a gas-filled spheroidal swimbladder immersed in a viscous fish body. However, target responses similar to those predicted theoretically for gas bubbles have been found in data collected in situ for estimating target strength from normal fish populations. With further theoretical and experimental work, high-order resonances could be a useful aid to estimating target size and possibly target species.

高周波スプリットビーム方式を用いたプランクトン計測装置の開発

We developed a high frequency split beam (SB) scientific echo sounder to measure the target strength of a zooplankton in situ. There are some issues for high frequency split beam method, namely, an accuracy of transducer, a high speed processing of phase detection and a calibration method. We discussed about the following provisions : Piezocomposite transducer, high speed phase detection device for mobile phone and tungsten carbide sphere.

Acoustic reflectivity measurments of sirenia (Florida manatees) at high frequencies

The Florida manatee (Trichechus manatus latirostris) is an endangered sirenian inhabiting shallow coastal waters of Florida (USA). Its population (∼3300) is dwindling, with 25%–30% of mortalities occurring due to collisions with boats (95 losses in 2002). An active sonar system that detects the presence of the animals, and hence alerts the boater, could help reduce the collisions. Experiments were performed on six captive manatees with several calibrated transducers in a 33×10×3 m3 pool to learn how much sound is reflected by these animals. At a frequency of 171 kHz we transmitted a brief sinusoid. An underwater video camera was aimed along the axis of the range direction of the sound transmission, permitting the co-registration of animal and acoustics. The camera and sonar were calibrated together by translating a 38-mm tungsten carbide sphere (TS=−39 dB@ 171 kHz) in a separate test tank facility. Results indicate that the reflectivity of the animals (not strictly target strength) is somewhat low, in the −49 to −40 dB range.