Ductile Fracture

Gold mineralisation at the Wallaby gold deposit is hosted by a 1,200 m thick mafic conglomerate. The conglomerate is intruded by an apparently comagmatic alkaline dyke suite displaying increasing fractionation through mafic-monzonite, monzonite, syenite, syenite porphyry to late-stage carbonatite. In the mine area, a pipe-shaped zone of actinolite-magnetite-epidote-calcite (AMEC) alteration overprints the conglomerate. Gold mineralisation, associated with dolomite-albite-quartz-pyrite alteration, is hosted in a series of sub-horizontal, structurally controlled zones that are largely confined within the magnetite-rich pipe. The deposit has a current ore reserve of 2.0 Moz Au, and a total resource of 7.1 Moz Au. TIMS U−Pb analysis of magmatic titanite and SHRIMP U−Pb analysis of gold-related phosphate minerals are used to constrain the timing of magmatism and gold mineralisation at Wallaby. Monzogranite and carbonatite dykes of the Wallaby syenite intruded at 2,664±3 Ma, at least 5 m.y. and probably 14 m.y. before gold mineralisation at 2,650±6 Ma. The significant hiatus between proximal magmatism and gold mineralisation suggests that gold-bearing fluids were not derived from magmas associated with the Wallaby syenite, particularly since intrusive events are unlikely to drive hydrothermal systems for more than 1 m.y. Analysis of the C and O isotopic compositions of carbonates from regional pre-syenite alteration and AMEC alteration at the Wallaby gold deposit suggests that AMEC alteration formed via interaction between magmatic fluids and the pre-syenite wallrock carbonate. The C and O isotopic composition of gold-bearing fluids, as inferred from ore-carbonate, are isotopically distinct from proximal magmatic fluids, as inferred from magmatic carbonate in carbonatite dykes. Thus, detailed isotopic and geochronological studies negate any direct genetic link between proximal magmatic activity related to the Wallaby syenite and gold mineralisation at Wallaby. The gold endowment of the Wallaby gold deposit, combined with the relatively low solubility of gold as thiosulfide complexes in low-salinity ore fluids at temperatures of about 300°C, implicates the influx of very large volumes of auriferous hydrothermal fluids. No large-scale shear-zones nor faults through which such large fluid-volumes could pass have been identified within the immediate ore environment, so fluid influx most probably occurred largely in a unit-confined, brittle-ductile fracture system. This was the ~500-m diameter AMEC alteration pipe, which was a brittle, iron-enriched zone in an otherwise massive conglomerate. During compressional deformation, the competency contrast between unaltered and AMEC-altered conglomerate created a zone of increased fracture permeability, and geochemically favourable conditions (high Fe/Fe+Mg ratio), for gold mineralisation from a distal source.

The present research reports comparative analysis of effects of cold working (CW) and annealing on tensile and impact-toughness behavior of 7075 Al alloy. Cold-rolled samples were annealed at various temperatures in the range of 225-345 °C for 5 min. A remarkable increase in ductility and impact toughness was observed when specimens were annealed at temperatures above 265 °C for 5 min. It was also found that cold rolling has a profound effect on strength anisotropy that enhances with amount of % CW. The maximum strengths were observed in the transverse direction in the investigated alloy. Cold rolling has been found to impart a significant effect on decreasing the impact toughness of alloy that enhance with amount of % CW; this loss in impact energy could not be compensated by recrystallization process. It has also been shown that impact test can be considered as a simple method for measurement of toughness and plastic anisotropy in sheet and plate. The analysis of the fracture surfaces with the scanning electron microscope presented dimpled morphology for the failure ductile mechanism in starting material and fibrous structure with some quasi-cleavage regions in cold-rolled samples, corresponding to the ductile to brittle fracture mechanism. © 2009 Elsevier Ltd. All rights reserved.

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A high-speed shear tester has been used to evaluate the interface strength of Pb-free solder balls with varying Ag and Cu content to a BGA laminate interposer with different finishes. The shear rate used is 0.45 m/s. Components with SAC405 and SnPb solder balls have been used as a reference. Results are compared with SAC305, SAC305 with NiGe addition, Castin 258 (2.5Ag-0.8Cu-0.5Sb), SAC105 (1.0Ag-0.5Ag), SAC101 (1.0Ag-0.1Cu-0.02Ni-xIn), SACX (0.3Ag-0.7Cu-0.1Bi), LF35 (1.2Ag-0.5Cu) and Sn3.5Ag. Electroplated NiAu finishes on the BGA laminate interposer studied come from different suppliers. Three failure modes are observed in the high speed shear test: brittle fracture in the intermetallic layer at the ball/interposer interface, ductile fracture in the solder bump and peel off of the solder pad from the interposer. Analysis of the fracture interface shows that almost all Pb-free solder alloys fail either in the intermetallic layer or by pad peel off. Only SAC101 and Sn3.5Ag show duct...

We present a combined experimental–numerical study on fracture initiation at the convex surface and its propagation during bending of a class of ferritic–martensitic steel. On the experimental side, so-called free bending experiments are conducted on DP1000 steel sheets until fracture, realizing optical and scanning electron microscopy analyses on the post mortem specimens for fracture characterization. A blended Mode I – Mode II fracture pattern, which is driven by cavitation at non-metallic inclusions as well as martensitic islands and resultant softening-based intense strain localization, is observed. Phenomena like crack zig-zagging and crack alternation at the bend apex along the bending axis are introduced and discussed. On the numerical side, based on this physical motivation, the process is simulated in 2D plane strain and 3D, using Gurson’s dilatant plasticity model with a recent shear modification, strain-based void nucleation, and coalescence effects. The effect of certain material parameters (initial porosity, damage at coalescence and failure, shear modification term, etc.), plane strain constraint and mesh size on the localization and the fracture behavior are investigated in detail.

... (2001). Modeling the hydrogen effect ahead of a crack tip under various hydrostatic constraint levels, and using the Rice and Tracy model (1969) for void growth, Liang et al. ... 2007) and acce-lerates void growth and coalescence at all triaxialities (1≤T≤3) in steel (Ahn et al. ...

A Ni-52 at. pct Ti shape memory alloy, cold drawn to 30 pct, was annealed at 1173 K for 1 hour, water quenched, and then subjected to differential scanning calorimetry (DSC). No evidence of the premartensiticR transformation was found during either the forward or the reverse transformation. Microstructurally, it was found that the alloy possessed a relatively large volume fraction (∼0.05) of coarse second-phase brittle particles. These precipitates acted as preferential sites for martensite plate nucleation and gave rise to a “starlike” morphology. The tensile and compressive properties of the alloy in the as-received condition were also investigated. The alloy exhibited relatively good ductility (fracture strain=0.28), which was attributed to its inherent ability to relieve or delay the development of plastic instabilities through rapid strain hardening. In addition, X-ray diffraction (XRD) of deformed specimens indicated the presence of an extraintensity peak corresponding to the B2 phase (110)B2 when the alloy was plastically deformed in compression. Accordingly, it is suggested that plastic deformation induces the reverse transformation to the B2 phase in highly stressed local regions. Transmission electron microscopy (TEM) of deformed martensite structures showed slip lines probably due to dislocation slip, as well as variant interpenetration. Besides, optical and scanning microscopy of regions adjacent to the fractured surfaces indicated that fine martensite plates and/or “apparent” new grains develop at regions of prior stress intensification (former crack-tip regions) during crack propagation.

The objective of the present work is to incorporate the effect of post-failure softening on fracture initiation modeling of steel alloy TC128 commonly used in railroad tank car manufacturing. The fracture initiation process is determined through a comprehensive mechanical tests, which includes tensile tests on standard dog-bone specimens, flat specimens with circular cutouts and central hole, notched round bars, punch indentation tests on circular blanks and special flat shear specimens. Ductile fracture toughness usually referred to as resistance curve is measured from two types of typical fracture mechanics specimen geometries: the compact tension C(T) and the three-point bending SE(B). Post-failure softening is then coupled with the constitutive model to describe ductile fracture propagation. It turns out that in the absence of softening in fracture, the crack growth rate increases with little resistance opposite of what has been observed in fracture response of typical steels. On the other hand, the post-failure softening algorithm increases the ductile resistance behavior of the material more realistically, compared to experiments and provides additional information regarding the state of stress governing the fracture process.

Tensile and plane-strain fracture toughness properties were obtained at cryogenic temperatures to compare the Al-Li alloys 8090, 2090, and WL049 and alloy 2219 in various tempers and specimen orientations. The strongest alloy at very low temperatures is WL049-T851, which is about 10% stronger than 2090-T81. Both alloys are considerably stronger than 2219-T87. Alloy 2090-T81 is tougher in the in-plane orientations (about 50%) than WL049-T851 at low temperatures; the higher in-plane toughness is attributed to the presence of less constituent particles and the tendency to crack out-of-plane or delaminate at low temperatures. This delamination tends to divide the moving crack, thus separating it into smaller regions where plan stress (rather than plane strain) conditions are conducive to increased toughness. Thus, a dichotomy: reduced toughness in the through-thickness or out-of-plane orientations leads to increased toughness in the in-plane orientations. In service, a leak in the tank ...

The Knowledge of metal flow and strain at fracture is most importance to the plastic damage in metal forming. Failure in metal working usually occurs as ductile fracture, rarely as brittle fracture. In terms of metal forming, the propagation of cracks is of little interest, since the main issue is to avoid their initiation. Therefore, the main effort has historically been placed not in developing a full mechanics analysis of ductile cracking, but simply on establishing criteria for predicting the fracture initiation sites and the level of deformation at which the crack will occur. A comparative study has been made on widely used criteria for predicting the occurrence of fracture in metal forming processes by using the upset test data of cylindrical specimens. A simple criterion, which is based on integrals of stress function, is proposed and its applicability is validated through the existing test data on commercial purity aluminium. The finite element analysis results of the complex geometries and loadings can be used in the proposed criterion for predicting the occurrence of defects. The proposed criterion acts as a limiting condition for the defects / cracks initiation under cold working conditions and takes into account the tensile stress ratio and tri-axiality.

Numerical simulations of straight tube hydroforming of a dual phase (DP600) advanced high strength steel were performed using a variant of the Gurson–Tvergaard–Needleman (GTN) constitutive model to account for the influence of void shape and shear on coalescence. The effect of axial-feed (end-feed) on damage development and formability is investigated for end-feed loads of zero and 133 kN. A parametric study was conducted to determine an appropriate void nucleation stress and strain and the numerical values compared with the experimental data. The calibrated GTN damage model gives good agreement with the experimentally determined burst pressure, formability and failure location with the best performance occurring for the high end-feed load.