Spalling Tests Research Articles

A modified Cochran–Banner spall model

The original Cochran–Banner spall model was modified to suit the usual definition of damage and to abandon the simplifying approximation as unnecessary. The strength function given by Cochran–Banner was maintained using the redefined damage and the correction concerning the volume of the mesh cells was realized considering it unnecessary to expect that it is much easier to open microcracks once they are formed than to strain the solid further. In the case of abandoning the simplifying approximation made by Cochran–Banner to calculate the damage, the redefined damage also does not become a new independent variable for which new dynamic laws would need to be specified. Once the spall strength was reached, the damage would be only determined by a series of closed equations including the stress.relaxation relationship given by the strength function, the energy conservation equation, the equation of state and the constitutive equations for the damaged aggregate. The modified Cochran–Banner spall model also included only two parameters: the spall strength and the critical damage, which relate to material properties and specific loading conditions. Comparison of theoretical and experimental results for some spall tests was performed. It was found that the computed free surface velocity profile of target or stress profile of interface between target and soft buffer in plane spall tests was sensitive to the spall strength and the critical damage in the modified Cochran–Banner spall model.

Evaluation of porcelain enamels of directional signs used in the UAE

Blue coloured enamel coatings on 3003 aluminium alloy panels have been produced. The enamels used to produce the coatings were of similar compositions except for titanium dioxide, colouring and other metal oxides. The first enamel composition was a standard one as recommended by the supplier and contains 7% of the expensive opacifier titanium dioxide. This recommended composition has been modified to form the second enamel. Higher amounts of the less expensive colouring and other metal oxides were added on the expense of titanium dioxide which was reduced to 1%. Different firing temperatures and enamel slip fineness were used to produce the modified enamel coatings. Scanning electron microscopy, accelerated weathering, spalling and dry erosion tests have been used to evaluate different enamel coatings. Results have shown that the modified enamel composition has produced coatings of comparable quality as compared to coatings produced using the supplier recommended composition. Firing the modified enamel below 500 °C results in enamel coatings of inferior quality, whereas firing at temperatures above 525 °C produces coatings of good performance. Coatings produced using small fineness have resulted in enamel coatings having pores of relatively smaller sizes.

Experimental study of A36 steel spall fracture

The preliminary results of A36 steel spall experiment are presented. Special attention is given to the heat treating conditions in the two-phase (ferrite and austenite) region and resulting microstructure after the spall loading condition. One of the fundamental principles of any thermomechanical processing in the two-phase region is the simultaneous superposition of microstructure evolution and mechanical behavior of particular phase. The degree of generated defects, cracks and phases, and phase transformation is decisive for the final microstructure and the fracture resistance. Preliminary results show the banded structure still exists after the spall test and, totally unexpected lack of the visible characteristic voids, cracks or shear instabilities due to the tensile loading at the mid plane of the sample.

Numerical modeling of rate-dependent debonding processes in composites

In this paper we discuss analytical and numerical results concerning rate-dependent dynamic crack processes in homogeneous and heterogeneous materials. Rate-dependency is introduced in the model through a newly formulated interface law. Three significant examples are presented: (i) the mode-I dynamic decohesion between two linear elastic half-planes under a tensile stress pulse; (ii) the uniaxial spall test and (iii) the debonding of a thin layer from a rigid substrate. The results show that rate-dependent cohesive laws can play an important role in dynamic crack processes.

Effect of material on spalling properties of railroad wheels

The objective of the present paper is to clarify the effect of material on spalling property, which is one of the typical damage that occur on the railroad wheel. Spalling tests, which consist of flat generation tests and rolling contact fatigue (RCF) tests, were conducted on 120 mm diameter disks made of four kinds of wheel steels. It was found that the maximum flat depth and the white layer thickness measured after the flat generation tests depended on a parameter of “the flat generation energy”. The maximum flat depth is not changed by material, but white layer thickness is changed by the hardenability of the material. According to the results of RCF tests by using TPs with/without flats, spalling property was determined by impact load and RCF property. The impact load which occurred due to flat depended on the shape of flat, however, it did not depend on material. Whereas, RCF property depended on the material. The lowest hardness material had the shortest life at the same Hertzian stress on the RCF test. The life of spalling seems to be determined by RCF property at the Hertzian stress magnified by the impact load.

Ductile damage of tantalum under spalling effects. Experimental and metallurgical analysis

In this paper, we examine the experimental and metallurgical features of ductile damage of some high purity tantalum under dynamic uniaxial strain loading. This particular sollicitation is obtained by performing plate impact experiments using a single stage light gas gun. Such spall tests are performed in the 5 GPa - 12 GPa range of shock pressures for a 1.5 μs pulse duration. On the one hand, free surface velocity has been measured by means of a Doppler Laser Interferometer in order to quantify the spall stress levels as a function of shock pressure. Theses results are compared to those of litterature and we found a good agreement. On the other hand, tests with soft recovery of shocked samples have been achieved for metallurgical analyses. These ones allow us to better understand the different stages of nucleation, growth and coalescence of microvoids. The advanced analysis performed in this work quantifies the size, shape and evolution of microvoids, which give us precise informations to propose well defined hypotheses fo further modelling of damage phenomena for tantalum.

Influence of the strain rate on the tensile strength in aluminas of different purity

It is well known that the properties of the materials may be different as the strain rate increases. Advanced ceramic materials such as aluminas, could present an increase in their strength as the strain rate becomes higher. In this paper the investigation is focused on the influence of the strain rate on the tensile strength of alumina. The influence of this variable on this property is experimentally analysed by means of two different kind of tests carried out from low to high strain rates. The splitting test of brittle materials is a testing technique widely used at low strain rates. It has been recently extended to dynamic conditions using the Hopkinson split pressure bar. In this work this method is used both in static and dynamic conditions with servohydraulic machines and a Hopkinson bar. The tensile strength of alumina has been measured at three different strain rates. The spalling test of long bars is an additional technique that provides the dynamic tensile strength of brittle materials in uniaxial conditions. The test procedure and the experimental details are also presented and discussed in a separate paper. This technique has also been used to measure dynamic tensile strength of alumina at higher strain rates. The influence of the strain rate on the tensile strength is presented and a comparison between the two kind of tests is also discussed. To identify the physical mechanisms causing the failure, a microscope analysis of fracture surfaces using SEM has also been performed. The study has been applied to the different specimens tested at low and high strain rates with the two different kind of tests, The results of the fractographic analysis are presented and discussed.

A wave propagation technique to measure the dynamic tensile strength of brittle materials

Brittle materials, as advanced ceramics, present a weak behaviour under tensile loads. For that reason, determination of the tensile strength in these materials is needed. A testing methodology to measure this property is not well defined, more highlighted at high strain rates, where dynamic loads make testing more complex. Uniaxial tensile tests are very difficult to reach out, and alternative tests have been proposed. Testing at high strain rates with three or four point bending tests or the diametrical compression of short cylindrical specimens are widely used. In those tests the stress state is not uniaxial and if the equilibrium in the specimen is not reached, interpretation of results becomes more complex. For that reason a new testing method has been proposed, the spalling test of long bars. This test can provide the tensile strength of brittle materials at high strain rates in uniaxial conditions. In this work, the experimental set-up developed in the Department of Materials Science of the Polytechnic University of Madrid is presented. The experimental device is based in the wave propagation in long rods and its reflection in a free end. In this paper, the equipment developed and used is explained in detail. With high-speed photography and an analytical analysis, the tensile strength can be measured. The stress wave reflection at the free end of the specimen bar causes the failure. This reflection progress is simulated by an analytical tool, and the stress state at the moment of rupture and the position of the first crack are measured, providing the maximum tensile stress in the material. It is also described the method to determine the tensile strength based on the data obtained from the instrumentation of the device and the measurements in the pictures taken. The results obtained in long rod specimens of alumina are presented.

Computational modelling of impact damage in brittle materials

A Lagrangian finite element method of fracture and fragmentation in brittle materials is developed. A cohesive-law fracture model is used to propagate multiple cracks along arbitrary paths. In axisymmetric calculations, radial cracking is accounted for through a continuum damage model. An explicit contact/friction algorithm is used to treat the multi-body dynamics which inevitably ensues after fragmentation. Rate-dependent plasticity, heat conduction and thermal coupling are also accounted for in calculations. The properties and predictive ability of the model are exhibited in two case studies: spall tests and dynamic crack propagation in a double cantilever beam specimen. As an example of application of the theory, we simulate the experiments of Field (1988) involving the impact of alumina plates by steel pellets at different velocities. The calculated conical, lateral and radial fracture histories are found to be in good agreement with experiment.

Spall in Metals Induced by Explosive Shock Loadings and Protective Measures Using Momentum Traps.

Spall tests for three kinds of materials (A12024, SS41, Cu) are conducted using a newly developed testing device. This experimental assembly generates triangular stress waves with various gradients-in plate specimens (50×50×20mm) by direct explosive loadings. The relationship between measured spall layer thicknesses (5-15mm)and the explosive (PETN) thicknesses indicate that a time dependence exists in spall phenomena of the metals. A computer program with a cumulative damage model was constructed, which has reproduced the basic characteristics of the observed failure in the metals. It is known that the stress wave reflected at the free surface can be prevented from reaching the specimen plate by spallation of the momentum trap or spall plate, which is mounted in contact with the specimen. The following spall test results for A12024 have verified this effect and the numerical analysis also has simulated the phenomena successfully.

Dynamic testing of ceramics under tensile stress

Three types of tests are considered: the three-point impact bending test, the Brazilian test and a modified version of the spalling test in which a specimen is loaded under uniaxial stress. The importance of conducting a sufficient number of experiments to interpret the results in terms of Weibull statistics and to achieve a simple state of stress is emphasised. Of the three techniques, the uniaxial spalling test satisfies both requirements and permits measurements at rates of strain of the order of 103 s 1 and above.

Additional Comparisons of Interlocked Fabric and Laminated Fabric Kevlar 49/Epoxy Composites

Compression, gas gun planar impact, and post-impact short beam shear test results are presented for a novel interlocked fabric reinforced Kevlar 49/epoxy composite. This material has roughly 4% fiber volume fraction in the through-the-thickness direction. For the purpose of comparison, similar results are also presented for a laminated Kevlar 49/epoxy composite. Both materials have a compressive stress-strain curve that can be approximated as bilinear with a secondary modulus of on the order of 10% of the initial modulus. Although the materials have comparable yield strengths (∼ 10% difference), their respective initial and secondary moduli are not in as close agreement (up to 50% difference). Gas gun planar impact spall test data indicate that relatively low levels of impact stress (∼1 kbar, ∼100 MPa) generate matrix cracking in both materials. The interlocked fabric's binder yarns, however, show no visible sign of damage even at an impact stress level of 5.1 kbar (510 MPa). Post-impact short beam shear test data for both materials show that once a threshold impact level is exceeded (∼1 kbar, ∼100MPa), specimen stiffness and load carrying capacity decrease as the impact level is increased. This is presumably because of mid-plane matrix cracks of increasing size and density. Even though the properties of the interlocked fabric reinforced composite are substantially reduced by impact at the 5.1-kbar (510-MPa) level, the binder yarns give the material a degree of integrity that would not otherwise exist. The interlocked fabric reinforced Kevlar 49/epoxy composite has a higher residual load carrying capacity than the laminated Kevlar 49/epoxy at all impact levels.

A large-scale impact spalling test

A unique test apparatus is described that effectively produces spalling on wear-resistant alloys and can be used to study the causes of spalling. The work was conducted by the U.S. Department of the Interior, Bureau of Mines, as part of an effort to minimize the consumption of strategic materials used during the mining and processing of minerals. The test utilizes balls 75 mm in diameter made of the test alloys, which are dropped a distance of 3.5 m. Multiple impacts over a range of energy are produced between the balls. The unique design of the test apparatus provides a multiplying effect that results in 30 000 or more total impacts per hour on 20 or so test alloys. The four major types of failure that were observed on 22 commercial and experimental alloys that received up to 300 000 impacts are discussed.

On the Thermal Properties of Electro-molten Mass Containing Dunite as Principal Ingredient

The studies of the thermal properties obtained by load and spalling tests of the electro-molten masses appeared in previous papers, J. Ceram. Assoc., Japan, 68 [10] 237, J. Ceram. Assoc., Japan, 68 [12] 294 (1960), were carried out. The matrix was separated by heavy solution, and was subjected to chemical analysis. Based on the summary of the results obtained the author disscussed the relation between the structure and the thermal properties of the electro-molten masses composed mainly of dunite.The results of load test, thermal expansivity, thermal conductivity as well as spalling have shown a considerable increase with the increasing ratio MgO/SiO2 of MgO containing masses. With the addition of calcic materials the properties of the mass were put under the control of the ratios MgO/SiO2 and CaO/SiO2, and up to 7.5% CaO was effective for improving the results of load and spalling tests, while more lime than this limit lowered the load bearing temperature.The effect of high aluminous materials were different in both sides of the line connecting MgO⋅SiO2 and 2MgO⋅SiO2 in the ternary system, MgO-SiO2-Al2O3. In the domain rich in Al2O3 gave the refractories of higher load bearing temperature than in the other one. In general, the addition of alumina lowered the thermal expansion and improved the thermal conductivity and spalling. A trend was found that SiO2, Al2O3, Fe2O3, CaO, and ZrO2 intermixed in the matrix of the mass as solution or as microcrystals.

A sonic spalling test : J. F. Clements and W. R. Davis, British ceramic society, Transactions, v. 57, Oct. 1958, p. 624–644

A sonic spalling test : J. F. Clements and W. R. Davis, British ceramic society, Transactions, v. 57, Oct. 1958, p. 624–644

The refractory brick and mortar for aluminium holding furnace and its baking method

This is to report on the study on the suitability of refractries for the lining of aluminium holding furnance. In this investigation, it was found that high alumina brick presented the best result. It was decided, as the result, the high alumina brick with the following properties is to be used for the actual operation.1. Chemical analysisSiO2 6.5%Al2O3 90.7%Fe2O3 1.9%TiO2 0.9%2. Reacted with molten alminium, and the content of SiO2 is slightly reduced.3. Slightly attacked by molten fluoride.4. The spalling test by rapid heating and cooling alternately more than 15 times.5. Correlative abrasion with alminium ingot 0.02g/100rev.6. Compressive strength 734kg/cm27. Apparent porosity 24.0%8. Water adsorption 8.4%9. Modulus of elasticity 5932kg/mm210. Apparent density 3.811. Thermal expansion (showed in Fig. 10)12. Water diffusion coefficient in the natural drying condition 0.0001m2/day13. Water diffusion coefficient in the forced drying condition 0.0024m2/dayIn case of lining furnace with this high alumina brick, the binder between the bricks should be half melted at 850°C, which is the finishing temperature of the furnace baking, and should be solidified at 750°C, the operating temperature of the furnace. Considering with this factor, special mortar of the following composition is to be used:Fused alumina in powder state 71.5%As best fiver 1.5%Sodium silico-fluoride 12.0%Soluble glass 15.0%Water operating amountThe furnace is reached to the operating condition without any trouble, when the above mentioned brick and mortar are used and the temperature of the furnace is raised in accordance with the temperature raising program. In this case the water content in bricks and the elongation of bricks took place during heating should be taken into consideration.

The Effect of the Difference of Chamotte on the Physical Properties of Pot for Optical Glasses

Forty parts of bonding materials composing of equal parts of gairomé-, kibushi-, roseki-clay and kaolin (Table 1) were mixed to 60 parts of various chamottes (totaling 80 kinds in Table 2) previously graded and weighed-out as 21 parts of coarse, 6 parts of fine and 33 parts of very fine, and the drying, burning and spalling tests were made. The results are summerized as follows.(1) At the burning temperature of chamotte within the range of this experiment, added alumiua scarcely sintered with kaolin and added quartzite aided sintering only when burned at high temperatures, but a remarkable sintering occured at lower temperatures in mixed chamotte of kaolin and feldspar.(2) Amount of water required for the same fluidity of casting slips with the same bonding material, but differing in kinds and in burning temperature of chamotte, increased linearly with the water absorption of the chamotte used. The amount of the drying shrinkage water of bodies cast from these slips remained nearly constant irrespective of kinds and burning temperatures of chamottes.(3) Between the bulk density of dried or burnt bodies and that of chamottes, a hyperbolic relation was found.(4) Bodies of as small porosity as necessary for a practical use could not be made by chamotte of kaolin mixed with more than 20% of alumina, nor with quartzite unless they were burned at very high temperatures. Chamotte made of kaolin with each 5% of quartzite and feldspar gave, on mixing with bonding materials and burning at high temperature, more dense bodies than those with addition of 10% feldspar.When the same mixture of 4 kinds of clays was used both for chamotte preparation and bonding material, more dense body was obtained than in cases when chamottes were made from single clay.(5) Resistance against spalling was tested at two temperatures, that is the temperature at which glass batches are thrown-in and the other is that of withdrawal of pots from furnace. Addition of feldspar to raw clays for chamotte preparation decreased spalling resistance, whereas addition of alumina or quartzite gave rise to no definite tendencies but these were dependent on the composition of mix and the temperature at which the chamotte was burned.(6) Spalling resistance seemed to be chiefly dependent on the physical properties of chamotte grain themselves, because adherence between chamotte and bonding material was not promoted by the use of the same raw material for the both of the two.(7) When pot shell, which had been used repeatedly, was quenched or cooled slowly and used as chamotte, no denser bodies were obtained than the chamottes from single clay. The difference in the cooling manner of the pot was not reflected on the obtained bodies.(8) Dense but spalling-resistant bodies could be easily obtained by selection of the proper chamotte. Chamotte made from roseki- or kibushi-clay was found to be good.

人工歯に関する研究 (第1報)

Low fusing porcelain teeth (800° to 900°C) was manufactured from borosilicate glass powder. And its superiority to other usual porcelain teeth was tested in comparison of their physical properties, such as: transparency, strength, expansion, chemical-proof, porocity and spalling test.

SUBSTITUTION OF DOMESTIC MINERALS FOR INDIA KYANITE: VI, REFRACTORY PROPERTIES OF GEORGIA MASSIVE KYANITE*

AbstractThe massive kyanite of Georgia is similar in structure to India kyanite, but it contains quartz with only occasional small amounts of corundum; sericite between the kyanite crystals is common. Excellent coarse grog (67% through 6‐ on 35‐mesh) can be produced from this kyanite. Maximum expansion of the rock during calcining occurs at 1400°C. with slight shrinkage thereafter.Brick were made of the kyanite grog with 3% and 10%, respectively, of EPK (Florida) clay; both had excellent resistance to load at elevated temperatures and met the reheat specifications of the Navy Department and the A.S.T.M. In the panel spalling test, Georgia kyanite brick showed approximately 20% loss, whereas India kyanite brick of the same grain size and clay content showed only 0.3% loss. Intensive prospecting is necessary and the unusual mining and cleaning operations with present known deposits make large‐scale commercial operation questionable.

Studies on Magnesium Silicates, “Steatite, ” Part VI

The authors, continuing the previous studies (This Journal, 1934, 42, 339, 471; 1935, 43, 55, 133, 263) on the fine refractory and electric insulating material “steatite”, reported the results of further comparative studies. In the following, the main points of the present communication are briefly abstracted from the original Japanese paper.(1) Several steatite specimens were stored for 3 months, after burning, in the air of the laboratory. All samples were seen expanded, especially the samples burned from talc only or with small addition of boric acid considerably expanded. The authors assumed that this expansion was owing to the moisture and carbon dioxide in the air.(2) To ascertain this expansion, 4 sorts of samples were put on to the hydrothermal treatment by heating in the autoclave of superheated steam of 10 atmospheric pressures and ca. 180°C for 3 hours. The samples No. 3 (talc only) and No. 4 (talc with 3% boric acid) disintegrated considerably, No. 2 (talc with 0.6% magnesium chloride) expanded, but No. 1 (talc with 3% alumina) was seen completely stable and in constant dimensions. So that, the reason of expansion was, as assumed above, clearly owing to the combination of water with the free silica of cristoballite form in the heat decomposed talc molecule, which is produced by calcining or burning talc (H2Mg3 Si4O12 or 3MgSiO3·H2SiO3) to anhydrous matter Mg3Si4O11 or 3MgSiO3·SiO2. This combination of water molecule with silica in the calcined talc and returning to talc molecule was accelerated by the hydrothermal treatment of superheated steam under high pressure, as above treated.(3) The modified spalling test or quick cooling test was applied to the steatite specimens of various burning conditions obtained in the foregoing experiments. The spalling test was modified by one of the present authors (S. Nagai) and carried on, as follows: the small cylindrical test pieces (dia. 2cm and height 2cm) were heated at 800, 1000, 1200 or 1300C for 30 minutes and quickly dropped in the water. The compressive strength and other physical properties were compared with those before this heat treatment, and the decrease of strength were principally discussed. The second modified test was also carried on, as follows: the test pieces applied to the repetitions of the heating at 800 or 1000°C for 30 minutes and then dropping quickly into water 2 or 3 times until to the complete disintegration of the test pieces, and the decrease of strength was principally compared. In the following tables are compared the results of these spalling or heat treatment tests, by using several steatite samples from talc, “Shuganseki”, etc.As seen from these results, the modified spalling test is suitably applicable to compare the resistibility of steatite to the quenching. The quenching temperature must be selected, (1) 1000°C or 12000°C for the test of comparing the decrease of strength over 50% by one quenching and (2) 800°C for repeated spalling test.(4) The authors will report in their next communication several further results of studies, (1) the special steatite obtained by mixing small quantity of alumina, zinc oxide, chrome oxide, etc., (2) expansion tests of various steatite specimens, (3) electric properties, etc.