Specimen blanks of additive-manufactured nickel Alloy 625 and Ti-6AI-4V were produced by the laser powder-bed-fusion process (L-PBF) with the principal test axis in both the Z direction (parallel to the build direction) and the X-Y direction (perpendicular to the build direction). The high cycle fatigue and corrosion fatigue properties of these metals were measured using R. R. Moore rotating cantilever fatigue tests, both in air and with a salt water drip on the test sections. Testing was conducted in order to determine the fatigue and corrosion fatigue limits of these materials at 10(8) cycles. The fatigue limit for L-PBF Alloy 625 material at 10(8) cycles in air was roughly 48 ksi (331 MPa), independent of build orientation. This is similar to the air fatigue limit of wrought material. The corrosion fatigue limit for L-PBF Alloy 625 material at 10(8) cycles in salt water was roughly 39 ksi (269 MPa), which was also independent of build orientation and slightly below the values for wrought material and values obtained by other investigators. The fatigue limit for hot isostatic pressed L-PBF Ti-6AI-4V material at 10(8) cycles in air was roughly 90 ksi (620 MPa), independent of build orientation. This is significantly better than the air fatigue limit of wrought material. The corrosion fatigue limit for L-PBF Ti-6AI-4V material at 10(8) cycles in salt water was roughly 78 ksi (540 MPa), which was also independent of build orientation, better than values for wrought material, and comparable to values obtained by other investigators. The fatigue crack growth rate behavior in air was characterized and compared with information available in the literature.

In 2006, EricksonKirk and EricksonKirk proposed a model describing a temperature dependence for upper shelf fracture toughness (JIc), based on the Zerilli-Armstrong (ZA) temperature dependence of the flow stress, that was common to the large number of ferritic steel datasets studied. The equation describing the temperature dependence of JIc was found to be a simple scalar multiple of the temperature dependence predicted by ZA for flow stress. Since that time a large dataset has been developed containing many experimental measurements of JIc for the purpose assessing and refining the previously proposed model. The new data, reported herein, validates the previously proposed model of JIc temperature dependence but suggests that revisions of the previously proposed model of JIc uncertainty are needed to ensure the applicability of the model to both low and high fracture toughness steels.

The mechanical, metallurgical and corrosion properties of Alloy 625 produced using the laser powder bed fusion (L-PBF) manufacturing process were investigated and compared with typical performance of the alloy produced using conventional forging processes. Test specimens were produced near net shape along with several demonstration pieces that were produced to examine the geometric complexity that could be achieved with the process. The additively manufactured specimens exhibited strength, fracture toughness and impact toughness that was equal to or better than properties typically achieved for wrought product. There was no evidence of stress corrosion cracking susceptibility in 3.5% NaCl solution at stress intensities up to 70 ksi-in1/2 after 700h exposure. The microstructure was equiaxed in the plane of the powder bed build platform (X–Y) and exhibited a columnar shape in the Z direction although there was not any significant evidence of anisotropy in the mechanical properties.

Recent experimental and computational work by Link and associates has demonstrated that relatively small (W = 150 mm) single edge notched tension specimens (SE(T)) can be used to obtain crack arrest data high in the ductile-to-brittle transition of ferritic structural steel using dynamic computational techniques if a thermal gradient is utilized to aid in the crack arrest. Testing has been reported on two important navy structural steels that clearly defines the relative capability of the two materials to arrest rapidly growing cracks. The HY100 material demonstrated the expected large difference between the initiation and Crack arrest toughnesses which has made it impossible in the past to measure crack arrest toughness for this material using the standard ASTM procedure (E1221) The HSLA-100 steel, however demonstrated a much higher crack arrest toughness and a correspondingly smaller drop in toughness below the initiation toughness. This small difference between initiation toughness and arrest toughness suggested that the E1221 procedure, using wedge loaded, compact crack arrest (CCA) specimens would be applicable to this material Two important issues could then be investigated using this material. First, having completed the expensive and relatively complex testing of the SE(T) specimens using tensile loading and a thermal gradient. a second, quite different geometry could be tested using the E1221 procedure. allowing an important comparison between the crack arrest measurements made using these two distinct geometries. Historically. obtaining crack arrest results using one test configuration has been so difficult, that there have been very few reports of results for the same material using two different test geometries. Transferability of the laboratory results to structural applications has thus been a matter of conjecture Furthermore. if the E 122 1 CCA specimens were strain gaged to obtain crack velocity data, and analyzed using the dynamic computational procedure used by Link on the SE(T) specimens, it would be possible to compare the results the E1221 static analysis with the results of the dynamic computation procedure to determine the degree of conservatism present in the E1221 standard procedureThe results of this work have shown that the crack arrest toughness results obtained on these two specimen geometries are similar and hence insensitive to the test geometry and the difference resulting from the application of the complex dynamic computational procedure or the E1221 static analyses is small. Published by Elsevier Ltd

During the 1990s considerable work was conducted to characterize the effect of biaxial loading on the ductile to brittle transition temperature. The work centered on a series of tests using large cruciform bend specimens from an experimental A533B test plate denoted as HSST Plate 14 (Heavy Section Steel Technology Plate 14). Recently a series of similar biaxial cruciform tests has been conducted on the steel used for an extensive European Round Robin that investigated the ductile-to-brittle transition master curve and associated T0 reference temperature. The results of these tests have been used to promote the concept of a “Biaxial Effect” which corresponds to a shift in the shallow crack transition master curve of +20°C or more when biaxial stresses are present, in comparison with the master curve for uniaxially loaded shallow crack specimens. A comprehensive analysis of the all of the available HSST Plate 14 data and data from two other structural steels was performed to investigate the extent of a biaxial effect on the reference temperature, T0. The analysis included many additional biaxial cruciform test results on three different materials. The results of all three materials discussed in this paper fail to clearly demonstrate that biaxial loading, imposed through the use of a cruciform specimen geometry, has an effect on the fracture toughness, characterized using a master curve approach and reference temperature T0. The analysis utilized in this paper assumes that the toughness distribution and temperature dependence of shallow cracked specimens can be modeled by using the master curve approach. This assumption has not been rigorously validated and would benefit from further study. Additional detailed stress analysis of the constraint evolution in the cruciform specimens may better define the precise conditions under which a biaxial effect on the fracture toughness could be realized.

J-integral resistance curves are developed for single edge bend [SE(B)] specimens of HY80 over a range of crack length ratios from 0.13 to 0.83. The wide range of constraint present over this range of crack length ratios results in J-integral resistance curves with nearly constant initiation toughnesses as measured by JIc, but with widely varying J-R curve slopes beyond JIc. A nearly linear relationship is shown to exist between the slope of the material J-resistance curve after 1 mm of crack extension and the Q parameter introduced by O'Dowd and Shih (Family of crack-tip fields characterized by a triaxiality parameter: Part I—Structure of fields. Journal of Mechanics and Physics of Solids, 1991, 39(8), 989–1015) to quantify elastic-plastic constraint. The constancy of JIc and the linear dependence of the tearing resistance on Q is used to develop an interpolation scheme to evaluate the J-integral resistance curve applicable to a specific structural application when the Q parameter can be estimated for the flaw geometry and loading present in the application.

An experimental investigation of fracture toughness in the ductile-brittle transition range was conducted. A large number of ASTM A533, Grade B steel, bend and tension specimens with varying crack lengths were tested throughout the transition region. Cleavage fracture toughness scaling models were utilized to correct the data for the loss of constraint in short crack specimens and tension geometries. The toughness scaling models were effective in reducing the scatter in the data, but tended to over-correct the results for the short crack bend specimens. A proposed ASTM Test Practice for Fracture Toughness in the Transition Range, which employs a master curve concept, was applied to the results. The proposed master curve over predicted the fracture toughness in the mid-transition and a modified master curve was developed that more accurately modeled the transition behavior of the material. Finally, the modified master curve and the fracture toughness scaling models were combined to predict the as-measured fracture toughness of the short crack bend and the tension specimens. It was shown that when the scaling models over correct the data for loss of constraint, they can also lead to non-conservative estimates of the increase in toughness for low constraint geometries.

Recent computational studies of the stress and strain fields at the tip of very sharp notches have shown that the stress and strain fields are very weakly dependent on the initial geometry of the notch once the notch has been blunted to a radius that is 6 to 10 times the initial root radius. It follows that if the fracture toughness of a material is sufficiently high so that fracture initiation does not occur in a specimen until the crack-tip opening displacement (CTOD) reaches a value from 6 to 10 times the size of the initial notch tip diameter, then the fracture toughness will be independent of whether a fatigue crack or a machined notch served as the initial crack. In this experimental program the fracture toughness (J{sub Ic} and J resistance (J-R) curve, and CTOD) for several structure alloys was measured using specimens with conventional fatigue cracks and with EDM machined notches. The results of this program have shown, in fact, that most structural materials do not achieve initiation CTOD values on the order of 6 to 10 times the radius of even the smallest EDM notch tip presently achievable. It is found furthermore that tougher materials do not seem to be less dependent on the type of notch tip present. Some materials are shown to be much more dependent on the type of notch tip used, but no simple pattern is found that relates this observed dependence to the material strength toughness, or strain hardening rate.