Improvement of Fracture Toughness Lanthanum Zirconate

Thermalbarriercoatings(TBCs)havefoundan increasingnumberofapplicationsinprotectinghigh temperaturemetalliccomponents,forexample,TBCsaredepositedontransitionpieces,combustion lines,first stagebladesandvanes,andotherhot pathcomponentsofgasturbineseithertoincreasethe inlettemperaturewithaconsequentimprovementof theefficiencyortoreducetherequirementsfora coolingsystem[1].Thereareseveralceramicsthat havebeenevaluatedasTBCmaterials[2].Lanthanum zirconatewasrecentlyproposedasapromisingTBC materia…     

Fracture Toughness of Cast Al-Zn-Mg Alloys

Compact tension specimens of as-cast Al-3Zn-2Mg and Al-7Zn-2Mg (in wt pct) alloys were subjected to fracture toughness tests at room temperature according to specification5 laid down in ASTM E-399-81. It was found that increasing the Zn content, grain refinement and increasing the solidification rate lead to an increase in the fracture toughness of the material.     

Fracture Toughness and Microcracks on Natural Apophyllite Crystals

Results on fracture toughness of natural apophyllite crystals when subjected to impact are presented. The morphology of the cracks and fracture has been studied. It is found that the crack formation does not show any anisotropic property and remains the same whatever may be the orientation of the crystal. The average values of the fracture toughness KC and brittleness index, as determined from measurements of crack length, are estimated to be 0.107 gμm-3/2and 4.19μm-1/2 respectively for the a(100) plane. The yield strength forα(100), p(111) and c(001) planes of apophyllite crystals for lower loads is 2250. 2160 and 1840 MPa and for higher loads is 1510, 1600 and 1430 MPa respectively     

Biaxiality Dependence of the Fracture Toughness for Glass in Plane Stress State

The fracture behaviour of glass in biaxial stress state has been investigated. Fracture toughness of disk specimen with a straight-through crack was measured under biaxial tension and uniaxial tension loads respectively. The difference between them and the reasons for the difference are discussed. The influence of the stress parallel to crack on fracture of brittle material was demonstrated in theory and experiments. The results show that plane stress fracture toughness of glass is not a material constant. and that the fracture toughness measured in biaxial tension state is higher than that measured under uniaxial tension. The conventional fracture criterion upon the stress intensity factor is questioned in the case of biaxial stress problem, and the strain dependence of crack growth is discussed.     

Comparisons of Experimental Fracture Toughness Testing Methods of Al6061–Graphite Particulate Composites

Journal of Failure Analysis and Prevention - This paper exhibits the investigative work conducted on fracture toughness of aluminum–graphite metal matrix composites. The materials chosen for...     

Effects of Microstructure on the Tensile, Fracture Toughness and Fatigue Behaviour of Gamma Titanium Aluminides

The effects of microstructure on the deformation and fracture behaviour of two-phase TiAl alloys were investjgated under monotonic and cyclical loading conditions, over a range of temperatu res.The tensile behaviour is analyzed for deformation temperatures between RT and 950℃, Fracture resistance behaviour and toughening mechanisms at RT and 800℃ are analyzed. and the inverse relationship botween ductility and toughness is explained using the crack initiation toughness. The preliminary results of load-controlled fatigue behaviour at 800℃ are interpreted using the tensile behaviour because deformation structure and fracture modes are similar under these two loading conditions     

Fracture Toughness and Thermal Shock Properties of Calcium Aluminate Composite with Controlled Duplex Structure

This study used monocalcium aluminate (CaAl2O4,CA) for producing ceramic composites with duplex microstructures by hydration and gelation reactions of the aluminate, and compared the properties with those made by a die-pressing process of mixed powders. Densification of the composite was optimized. The microstructure of sintered bodies, the fracture strengths and toughness of the composites with and without thermal shocking was characterized by different techniques. Experimental results show that the green body with the addition of CA resulted glomerated platelets or uniform distribution of platy CA6 grains. The former, which appeared a duplex microstructure consisted of dense matrix and distributed clusters of CA6 platelets, performed an improvement on toughness and thermal shock resistance. Toughness mechanisms of samples with duplex microstructure are also investigated.     

ANN Optimization Method for High Strength High Fracture Toughness Steels

The two-target optimization problem for high strength high fracture toughness steels has been investigated. An effective method for two-target optimization of multi-variable non-linear complicated system is developed by combining simulated annealing algorithm with artificial neural network     

Prediction of Fracture Toughness of Reactor Pressure-Vessel Steels Using the “Master Curve” Concept and Probabilistic Model

Using a probabilistic model and the Master curve approach, the temperature dependence of the brittle fracture toughness of reactor pressure-vessel steel 15Kh2NMFA in the initial state and highly embrittled state is predicted from the results of fracture toughness testing of a cracked Charpy-type specimen at a given temperature. A comparative analysis has shown that for the steel in the initial state the curves calculated by the probabilistic model and by the Master-curve approach are in good agreement. By testing compact-tension specimens of embrittled 2T-CT steel in a wide temperature range the authors have obtained experimental fracture toughness values and compared them with the calculated curves. It is demonstrated that, in the case of the embrittled steel, the curve as calculated by the Master-curve approach fails to describe adequately the experimental results, while the curves plotted by the probabilistic model agree well with the experimental fracture toughness values.     

Fractal Microstructure of Fracture Surfaces and Fracture Energy of Metals

Using a fractat model, we give a new interpretation of the reversed sigmoidal curves of fracture surface profile length obtained in some experiments. It is pointed out that a single parameter (fractal dimension D) is not sufficient to characterize a fractal curve completely. It is shown that the initiator length L0 is also important to characterize a fractal curve. We have derived a formula which correlate the fracture energy with the fractal parameters of the fracture surfaces and analyzed some experimental data.     

Factors Affecting the Relation of Fracture Toughness V_(GC) with Critical Void Growth Ratio R_C/R_O

The relationship between fracture toughness VGC and critical void growth RC/RO was studied for ten kinds of Steel. The macroscopic fracture toughness VGC was determined by using notched tensile specimens. and the microscopic parameters of critical void growth ratio RC/RO were quantitatively measured under SEM. Then, the coefhcient C in the relation VGC = C In(RC/RO) proposed in author's past work was specifically explored. The correlation of C with tensile proderty parameter φ=σyδ/(Eφn) was presented for the Steel investigated, and the effects of low temperature on C were also discussed. Results show that the coefficient C is linearly related to the parameter and insensitive to low temperature.     

Evaluation on Fracture Toughness at Dynamic Loading for Welded Joint Based on the Local Approach

The changes in mechanical properties and fracture toughness by dynamic loading were investigated with experiments. The parameter R, which can reflect the effect of the loading rate and the temperature rising during the high loading rate, could be employed to describe the constituent relation for the typical structure steel and its weld metal. The dynamic loading effect on the stress/strain fields and the temperature variation in the vicinity of the crack tip was analyzed by the finite element method, the dynamic fracture behavior was evaluated based on the local approach. It has been found that the Weibull stress is an effective fracture parameter, independent of the temperature and the loading rate.     

A New Method for Determining J_(IC) of High StrengthHigh Fracture Toughness Steels by SingleThree Point Bend Specimen

A single three point bend specimen compliance method for determining JIC of high strength high fracture toughness steels is presented and a formula for calculatinff J-integral is proposed as follows.It is simple and valid for high strength high fracture toughness steels. The values of JIC and KIC measured by this method are in good agreement with those measured by standard test method.     

Thermal Characteristics of Gel Grown Lanthanum Heptamolybdate crystals

Thermal characteristics of Ianthanum heptamolybdate crystals grown by gel technique, employing thermoanalytical techniques, viz. TG, DTA and DSC, are reported. It is established that the rare-earth lanthanum heptamolybdate crystals are associated with thirty water molecules;the composition being La2Mo7O24.3OH2O. It is shown that all the thirty water molecules associated with lanthanum heptamolybdate crystal are lost during its decomposition, leading to its anhydrous form. Results obtained on application of TG based models, viz. Horowitz-Metzger,Coats-Redfern and Piloyan-Novikova and of DSC based methods viz. Roger-Morris-Smith and Barret, regarding solid state reaction kinetics are also reported. The random nucleation model is shown to be the one that is relevant to the decomposition of lanthanum heptamolybdate. The kinetic parameters, viz.the order of reaction. frquency factor, energy of activation and entropy using above mentioned models are computed and shown to bear reasonably good agreement     

Fracture Analysis of Composites in High-speed Tension

In this paper the results of a high-speedtension experiment of the SiC_w/Al compositehave been reported and a simplified theoreticalmodel has been developed to study the fracturemechanism of composites in high-speed tension.This theoretical model provides a new explanationfor the increase of dynamic fracture strengthof composites in high-speed tension.     

Effects of B and Ti on the Toughness of HSLA Steel Weld Metals

Effects of microalloying Ti and B on themicrostructures and low temperature toughness ofmanual metal arc (MMA) deposits were investi-gated.Weld metals containing 200-300 ppm Ti and29-60 ppm B deposited by manual coated elec-trodes provided an optimum low temperaturetoughness.The addition of B in weld metals low-ered the γ→α transformation temperature whichpromoted the acicular ferrite (AF) transformation.Solid solutioned B suppressed grain boundaryferrite as well as side plate ferrite formation andbenefited the acicular ferrite formation.Titaniumprotected B from oxidizing as well as nitriding andformed Ti-Mn silicate inclusions.Ultra-high volt-age electron microscope analyses showed that TiOstructure in the Ti-Mn silicate inclusions was thefavorable nucleation site for acicular ferrite forma-tion.     

Fractal Dimensions of Hydrogen Induced Brittle Fracture of Titanium Aluminide

The relationship between the stress intensity factor K_1~* required for brittle crack initiation and propa-gation and the fractal dimension D_F of the fracture surface was derived,i.e,InK_1~*=(1/2)In2γE'+(1/2)In(d_f/L_0)(1-D_F)The real surface energy can be calculated based on the measured linear relation of the InK_1~* vs D_F,The equation is not only suitable for the overload fracture but also for the delayed fracture,e.g.hydrogen induced cracking (HIC) and stress corrosion cracking (SCC).The experiment resultsshowed that the hydrogen induced delayed cracking occurred in the Ti-24AI-11 Nb alloy during dy-namic charging,and the threshold stress intensity factor was very low,i.e..K_(IH)/K_(IC)= 0.43.The ex-perimental relationship between the stress intensity factor K_1~* and D_F was consistent with the theo-retical equation.     

The Morphology of Rolling Contact Fatigue Fracture of Hardened Steels

Rolling Contact Fatigue(RCF) is a cumulativedamage phenomenon when metals are subjectedto repeated contact stresses. The fomationof pitting on the contact surface is the resultof the rolling contact fatigue. The morphologiesof rolling contact fatigue fracture of the har-dened steels (86CrHoV7, 42CrMo) show that strongresemblance in fractuye mechanisms exists betweenrolling contact fatigue and uni-axial fatigue.Since fatigue striations are hardly observedin hardened steels under uni-axial fatigue,it is interesting to note that the state ofstress in rolling contact fatigue is more favor-able to ductile fractures than in uni-axialfatigue.