Crack Propagation Energy Research Articles

Dependence of unit crack propagation energy on chemical composition of AMg6-type alloys

Dependence of unit crack propagation energy on chemical composition of AMg6-type alloys

Measurement of the effect of microstructural variations on the energy of (Co, Ni)-Cr23 C6 eutectic

The measurement of sector areas of load-deflection curves in the Tattersall-Tappin test permits evaluation of the fracture energy dissipated by the microstructure during crack propagation. This method has been applied to the oriented pseudo-binary (Co, Ni)-Cr23C6 eutectic alloys which exhibit an irregular, continuous network of brittle carbides within a ductile (Co, Ni, Cr) phase. In spite of the complexity of the microstructure analysed, the method proposed for measuring the fracture energy seems to be capable of revealing the fundamental influence of the size, volume and properties of the phases on the fracture energy of the alloys. An increase in the fracture energy for crack propagation has been observed with: (a) an increase in the size (spacing) of the phases for a constant volume fraction; (b) an increase in the volume fraction of the ductile phase; (c) a progressive increase of the Ni content of the alloy (for values above 5 wt % Ni); the highest values being observed for the pure ternary system: Co-Cr23C6 and Ni-Cr23C6.

Determination of the crack propagation energy in impact bending of coated materials

Determination of the crack propagation energy in impact bending of coated materials

アルミニウム合金Ａ５０８３の溶接空属の衝撃特性に及ぼす均質化の影響

5083 aluminum alloy plate of 10 mm thickness was welded by MIG pulse arc process. Then, impact test was performed on base and weld metal at room temperature, -75 and -196°C. For the weld metal, Charpy impact test was also performed on the weld metal after homogenization at 500°C for 20 hours.Mg content dissolved in the weld metal was approximately the same near the fusion boundary as near the center of the weld metal and was 2.87 and 2.80%, respectively. On the other hand, the Mg content dissolved in the base metal was 4.45%. When the homogenizing was performed on the weld metal at 500°C for 2 hours, the dissolved Mg content increased to 4.10% and the content did not change after longer homogenized time.Charpy impact values were approximately the same at -196°C as at the room temperature for the base metal. For the weld metal, however, the values at -196°C were lower than those at room tem-perature. This phenomenon was mainly due to the decrease of crack propagation energy. After the homogenization of the weld metal the Charpy impact values increased. Besides, crack initiation energy increased approximately linearly when the dissolved Mg content increased.On the fracture surface of the weld metal dimple patterns were observed at room temperature and quasi-cleavage like structure was mainly observed at -196°C. After the homogenization of the weld metal, the dimple patterns were observed on considerably wider area of the fracture surface even at -196°C

Influence of copper additions on the basal cleavage in beryllium single crystals at room temperature

In order to study the influence of Cu-alloying on the susceptibility of Be to cleavage along the basal planes, a series of single phase alloys containing up to 5 at. pct Cu in Be were prepared and tested at room temperature by the DCB technique. Copper additions were found to influence strongly the plastic events induced by the shear stresses acting at the crack tip. The crack propagation energy increases with Cu content up to about 1.2 at. pct Cu and decreases with further additions. The maximum value attained at 1.2 at. pct Cu is about seven times that of pure Be. This remarkable initial increase in the crack propagation energy can be accounted for on the basis of the higher energy needed to activate basal and prism slip due to solid solution hardening. In alloys containing more than about 1.2 at. pct Cu, twinning is found to be the most prominent deformation mechanism. The propensity to twin is observed to increase with increasing Cu content, and it is assumed that this reflects a corresponding decrease in the twinning energy. Since twin boundaries are highly susceptible to cleavage cracking, a decrease in the crack propagation energy results which has the effect of increasing the tendency of Be to fracture in a brittle manner in the alloys with higher Cu contents.

Fatigue crack propagation in aluminum-base copper alloys

Fatigue crack propagation ratesda/dN in binary Al alloys with 3.6 wt pct Cu and 6.3 wt pct Cu and commercial 2024 aged at 21°C were compared with 99.95+ wt pct aluminum. Omitting an anomalous region at lowΔK, the extrapolated rates for “pure” aluminum are more than 100 times greater than those in the three alloys at the same ΔK. The data for the alloys fit into a single scatter band of a factor of three. It was suggested thatda/dN varies inversely with the square of the strength of the alloy but that another parameter related to the fatigue crack propagation energy per unit area is also important. Theda/dN vs ΔK curves were determined for 3.6 wt pct Cu single crystals aged seven days at 21°C which containGP zones and two and seven days at 160°C which contain mixtures ofθ′ andθ′’. No systematic variation of (da/dN Δ with crystallographic orientation was discerned, but the naturally aged specimen had a strong orientation dependence on crack initiation. At low ΔK 21°C aged specimens gave the lowestda/dN while at high ΔK the warm aged specimens gave the lower values ofda/dN. Measurement ofda/dN vs ΔK curves were conducted on specimens of 3.6 wt pct Cu with 1 mm equiaxed grains aged for various times at 130°C, 160°C, and 190°C. All warm aged specimens experienced brittle intergranular fracture at sufficiently high ΔK. The transition ΔK where intergranular fracture first appears is inversely proportional to the aging temperature. The change of fracture mode from intra to intergranular occurs gradually over a broad range of ΔK which shifts to lower ΔK with increase in aging temperature.

Effect of austenitizing temperature on toughness of martensitic steels

"Effect of austenitizing temperature on toughness of martensitic steels." Metals Technology, 3(1), pp. 208–209

Fracture properties of rigid polyurethane foams

AbstractThe fracture behavior of rigid polyurethane foams has been investigated and is shown to obey the Griffith criterion for fracture in so far as the predicted behavior of tensile strength on the size of artificially introduced cracks is concerned. The energy for crack propagation (fracture surface energy) has been measured as 91.4J/m2. From this result, the intrinsic flaw size of the material is calculated. This value was found to be within the range of cell dimensions of the material.

Ａｌ‐Ｍｇ‐Ｚｎ合金およびその溶接部の切欠じん性と破壊特性

Notch toughness and fracture characteristics of Al-Mg-Zn alloys and their welds were studied by mea-suring the notched and unnotched tensile properties, Charpy impact value, crack propagation energy in a modified Navy tear test and fracture stress in a deep-notch test.With increasing Mg content or with decreasing Zn content in the alloys with Mg+Zn≈6% (constant), ductility and toughness tended to increase, whereas strength tended to decrease. Al-4.5%Mg-1.5%Zn alloy was superior to 5083 alloy in ductility as well as strength.Al-4%Mg-2%Zn alloy with comparable ductility to 5083 alloy was superior in strength to Al-4.5%Mg-1.5%Zn alloy, while both alloys were inferior to 5083 alloy in toughness evaluated by Charpy impact value and crack propagation energy in the tear test.However, Al-Mg-Zn (Mg>Zn) alloy welds showed comparatively stable fracture with little reduction of fracture stress in the deep-notch test at cryogenic temperature, while the dimple pattern disappeared and intergranular cracking was observed in fractography with lowering the testing temperature.

The effect of the carbide phases on the crack grow of 0.5 pct Mo-B steels under impact, cyclic, and monotonically increasing loading

A study of the influence of carbide phases on the cracking resistance of as-quenched and of quenched and tempered 0.5 pct Mo-B steels was made using notched or notched and precracked specimens that were subjected to impact, cyclic, and monotonically increasing loading. The carbide influence on fracture, while limited in extent, was found to increase as load, loading rate, volume fraction, and particle size increase. The results for the asquenched condition showed that the susceptibility of these steels to crack initiation under impact loading at temperatures below - 100°F is greater when even a small amount of titanium carbide (less than 0.2 vol pet of 1 to 5 μm particles) is present than when none is present. At room temperature, this same carbide concentration has no influence on impact properties, fatigue-crack initiation (in the presence of a notch), fatigue-crack growth rate, or the ductile fracture resistance under monotonically increasing loading at slow strain rate. In the case of the quenched and tempered materials, the alloy containing a large amount of M23C6 (2 vol pct of 1 to 10 μm particles) exhibited behavior similar to that observed in the as-quenched materials containing titanium carbide. That is, the presence of M23C6 was associated with increased susceptibility to crack initiation for impact loading at low temperature. In addition, at room temperature this alloy had a reduced impact energy for crack propagation. For monotonically increasing loading at slow strain rate, this same carbide distribution had no influence on the net section stresses required to initiate stable or unstable crack growth. These stresses fall closely in line with, respectively, the yield stress and tensile strength of the material. The alloy containing M23C6 required less crack opening for a given crack extension—an effect most pronounced after maximum load. Finally, some attention is directed to the use of Charpy test data to assess fracture resistance for modes of loading other than impact.

Influence of Iron and Silicon on Toughness and Fracture Characteristics of Al–Mg–Mn and Al–Zn–Mg Alloys

Experiments were performed on Al–Mg–Mn and Al–Zn–Mg alloy plates to investigate the influences of iron and silicon on notch toughness and tear resistance and their fracture characteristics. Notch toughness was evaluated from the ratios of notch-tensile strength to tensile strength (notch-tensile ratio) and notch-tensile strength to yield strength (notch-yield ratio) and the Charpy impact value, and the tear resistance was determined from the crack initiation and propagation energies, particularly by the latter, in a modified Navy tear test.The notch toughness and tear resistance of fully annealed Al–Mg–Mn and naturally and artificially aged Al–Zn–Mg alloy plates were markedly reduced with increasing amounts of iron and silicon. Iron, silicon and iron + silicon, when these contents were equal, had similar influence on the notch toughness and the tear resistance. In a strict sense, however, the reduction of toughness due to silicon was most remarkable.As the amounts of iron and silicon were increased, the dimple pattern associated with ductile fracture gave way to a quasi-cleavage pattern associated with a relatively brittle fracture, and an intergranular rupture along the fibrous grain structure was observed. Fine lamellar cracks occurred near second phases containing iron and silicon. From these observations, it seems very likely that the crack initiation and propagation in the Al–Mg–Mn and Al–Zn–Mg alloys are closely related to the distribution of iron and silicon. However, it is necessary to consider some supplementary mechanisms, if iron and silicon are contained separately.

Estimation of the impact strength of steels at cryogenic temperatures

1. The character of the stress state in the vicinity of notches in impact specimens, which is determined by the notch, has a substantial influence on the γ → α transformation taking place as a result of cooling and deformation of steels with metastable structures; this leads to changes in the ductility of steel. 2. Increasing the notch depth in impact specimens of metastable austenitic steels produces a decrease in their impact strength, especially in the temperature range of intense γ → α transformation. 3. The reduction produced in the impact strength of structurally stable steels by increasing the notch depth is much smaller than in the case of metastable steels, since it is associated only with a change in the stress state. 4. The energy of crack propagation in steels of various strength and with various structures can be determined by the Gulyaev and Drozdovskii methods in the entire range of cryogenic temperatures. 5. Electron fractography of fracture surfaces of impact specimens is quite an effective method of estimating the impact properties of cryogenic steels.

The energy of crack-propagation in carbon fibre reinforced resin systems: Beaumont, P. W. R. and Harris, B. Journal of Materials Science, Vol 7, No 11 (Nov 1972) pp 1265–1279

The energy of crack-propagation in carbon fibre reinforced resin systems: Beaumont, P. W. R. and Harris, B. Journal of Materials Science, Vol 7, No 11 (Nov 1972) pp 1265–1279

Stress-corrosion cracking of Ti-8Al-lMo-lV in aqueous environments: 1. The kinetics of subcritical crack propagation

Precracked specimens of Ti-8Al-lMo-lV were tested in salt-water, and the subcritical crack velocity was measured as a function of applied stress-intensity. The minimum applied stress intensity which produces subcritical cracking,K Iscc, varies inversely with the average chloride-ion concentration of the environment, butK Iscc does not vary significantly with temperature. Plots of subcritical crack velocity,a, against applied stress intensity,K I, reveal two types of cracking behavior. At low stress intensitiesa is approximately proportional toK I (Stage I crack propagation). At high stress intensities,a is approximately constant, independent ofK I (Stage II crack propagation). The apparent activation energy for subcritical crack propagation is 5600 cal-(g-mole)-1, anda ∞ [Cl-]1/6. It is suggested that the instantaneous subcritical crack velocity is limited by the rate of production or by the diffusion of some embrittling species.

Influences of Fe and Si on notch toughness and tear resistance of Al-Mg-Mn alloy plates and welds

Experiments were conducted to study effects of Fe and Si on notch toughness and tear resistance of Al-Mg-Mn alloy plates and welds. Notch toughness was evaluated by a ratio of notch-tensile strength to tensile strength (notch-tensile ratio), that of notch-tensile strength to yield strength (notch-yield ratio) and Charpy impact values and tear resistance by crack initiation and propagation energies in the Navy tear tests.The notch-tensile ratio, the yield ratio and the Charpy impact value of annealed plates and welds as well as crack initiation and propagation energies in the Navy tear test were reduced with increasing amounts of Fe and Si. Fe, Si and Fe + Si, if these contents were equal, had the similar influence on the notch toughness and the tear resistance. However, in a strict sense, the effect of Si was most notable.As the amounts of Fe and Si increased, the dimple pattern associated with ductile fracture gave way to the quasi-cleavage pattern associated with a relatively brittle fracture and the intergranular or interdendritic rupture was also noted. Fine lamellar cracks were observed in second phases containing Fe and Si. From these observations, it was considered that the crack initiation and propagation in the Al-Mg-Mn alloy plates and welds were closely related to the distribution of the second phases.

The energy of crack propagation in carbon fibre-reinforced resin systems

The energy expended during controlled crack propagation in unidirectionally reinforced composites of carbon fibre in a brittle resin matrix has been evaluated in terms of the energy dissipated during fibre-snapping, matrix-cracking and fibre pull-out. The work of fracture, γF, is found to depend principally on the frictional shear stress at the fibre/resin interface opposing pulling out of broken fibres. Differences in γF for carbon fibre/resin composites exhibiting a range of interfacial shear strengths and void contents have been explained with reference to variations in fracture surface topography of the fibrous composites. The effect of environment on properties of the interface and work of fracture was also investigated. The energy required to propagate a crack has been compared with the energy for fracture initiation, γI, using a linear elastic fracture mechanics approach. It was found that fibre pull-out energy is the principal contribution to γF, and γI is similar to the elastic strain energy release rate at the initiation of fracture of a brittle, orthotropic solid. For crack propagation parallel to fibres, γF and γI are similar and not unlike the fracture surface energy of the resin alone. The strength of the interface is important only in so far as it affects the value of γI.

The Fracture Toughness of Epoxy-glass Bead Composites

Abstract The plane strain fracture toughness of epoxy resins and glass bead filled epoxy composites has been investigated. It was found that the energy required for fracture depended primarily on the ability to dissipate energy in the polymer phase. At low temperatures, where the epoxy was relatively brittle, the addition of glass beads increased the fracture energy and induced roughness in the otherwise smooth fracture surface. At higher temperatures and/or increased catalyst concentration, the unfilled epoxy became more ductile, its fracture surface became rougher, and its fracture energy was increased. When the epoxy was ductile, the addition of beads tended to decrease the fracture energy because of a reduction of the amount of polymer on the fracture surface. Adhesion of the matrix to the glass beads was only important when the polymer was ductile. Improved adhesion permitted the beads to constrain polymer flow and decrease the fracture energy. Poor adhesion permitted flow around the beads which required additional energy for crack propagation. At low temperatures, where the matrix was brittle, the additional constraints caused by adhesion appeared to make little difference. Water absorption resulted in plasticizing the polymer, destroying the interface, and probably destroying the polymer near the interface. Short term immersion increased the toughness because of the additional ductility. Long term immersion tended to reduce the toughness. An effective coupling agent minimized this reduction, thereby showing that improved adhesion can improve the environmental stability and extend the useful life of the material.

Fracture characteristics of some aluminum alloy sheets in Charpy impact test at super-low temperatures

Aluminum alloys have recently been used as cryogenic structural materials. The purpose of the present paper is to study tensile properties and behavior at impact test of T-4 treated Al-Zn-Mg, annealed Al-Mg and T-6 treated Al-Mg-Si alloys between room temperature and -196°C.Although no distinct reduction of ductility was observed in tensile test at low temperatures, instrumented Charpy impact test of Al-Zn-Mg and Al-Mg alloys showed a reduction of notch toughness at -196°C: Toughness was good in the following order; Al-Mg alloy> Al-Zn-Mg alloy> Al-Mg-Si alloy.Low temperature embrittlement of Al-Zn-Mg alloy was due to a decrease of crack-propagation energy. Crack-initiation and crack-propagotion energies were reduced in Al-Mg alloy. Low temperature fracture surfaces of these alloys showed laminated fracture facets. These facets were probably introduced by low temperature brittle fracture of precipitates at extremely elongated grain boundaries.It was found that the unstable rapid fracture occurred in press boundary notch specimens of Al-Zn-Mg and Al-Mg-Si alloys. The fracture toughness value for these alloys was estimated to be about 1 kg-mm/mm2.

The relation between microstructure and toughness in 7075 aluminum alloy

Electron microscopy, fractography, and notched tear tests have been used to investigate the effects of heat treatment upon the fracture behavior of aged 7075 aluminum alloy sheet. Toughness, as measured by crack propagation energy, decreases as the yield stress increases; the toughness of an overaged structure is inferior to that of an underaged structure at the same yield stress. The decrease of toughness with increased aging time is accompanied by a change in fracture mode from predominantly transgranular to intergranular. Transgranular fracture proceeds by dimple rupture and is facilitated by chromium-rich particles which are dispersed throughout the microstructure. Intergranular fracture proceeds by the fracture of grain boundary precipitate particles. The variation of fracture mode with aging time is attributed to a steady decrease of the intergranular fracture stress relative to the transgranular fracture stress, due to increasing grain boundary particle size. A possible explanation of this effect is discussed using the stress concentration due to colinear crack arrays as an analogy. The effects of quenching variations and two-step aging are discussed. It is shown that, in aged 7075, microstructural variables such as the width of precipitate-free zones and the nature of the matrix precipitate do not have a controlling effect on toughness.

Fracture and tearing in oriented polyethylene

Measurements of energy for crack propagation (fracture surface energy) have been made on low-density and high-density polythenes both in the undrawn state and in different states of orientation produced by drawing under various conditions. Both cleavage and tear tests were employed. For the unoriented materials the values of fracture surface energies were in the range 104 to 105 J m−2.With increasing orientation (represented by birefringence) the energy for crack propagation parallel to the direction of orientation fell by a factor of approximately 100. The differences between the low-density and high-density polymers, and between the different types of low-density polymers examined, were comparatively slight. Measurements of crack tip diameter showed a direct relation between this quantity and fracture surface energy. From their comparable studies of the tearing of rubbers Rivlin and Thomas have interpreted such a relationship as implying that the high values of fracture surface energy arise from the work required to deform the material in the crack tip up to the point of rupture. On this basis the reduction in fracture surface energy with increase in orientation is a direct result of the reduction in the diameter of the crack tip.