Analysis of fatigue failure mode transition in load-carrying fillet-welded connections

A quantitative weld sizing criterion for fatigue design of load-carrying fillet-welded connections

Two mechanistically different modes of EIC have been identified using high-resolution X-ray computed tomography and scanning electron microscopy (SEM) in sensitized AA5083-H131 that had been pre-exposed to 0.6 M NaCl prior to interrupted slow strain rate testing (SSRT) in the short transverse direction while exposed to laboratory air (50% RH). One mode, shown to propagate when local stress intensity factors are in the range of 4–12 MNm‐3/2, is the well-known ‘classic’ form of intergranular stress corrosion cracking, Type-1 cracking, which would not initiate and propagate in dry air, irrespective of pre-exposure or sensitization. The second mode of cracking, identified presently as Type-2 cracking, is associated with sudden load-drops occurring after the UTS during SSRT. Type-2 cracking propagates at higher local stress intensity factors (above 12–15  MNm-3/2) with significantly higher average growth rates than Type-1 cracking, involves the sudden simultaneous mechanical linkage of multiple fully-isolated regions of damage, pre-determined during pre-exposure to NaCl solution and generated during straining in laboratory air. Differences in the extent of Type-2 cracking for pre-exposed samples tested in ‘dry’ air compared to laboratory air (50% RH) were marked, with that in dry air being limited to isolated patches. High-resolution 3D tomography and detailed SEM has been used to distinguish these two mechanistically different modes of EIC. Implications for a role of hydrogen embrittlement during EIC are discussed.

Improved understanding of environment-induced cracking (EIC) of sensitized 5XXX series aluminium alloys

The effect of reversion heat treatment on the degree of sensitisation for aluminium alloy AA5083

Strength analysis of fillet welds under longitudinal and transverse shear conditions

Structural aluminum alloys are used in marine applications where light weight and increased speed are paramount. The 5xxx series alloys are the ideal choice, providing an optimum combination of as-welded strength and general corrosion resistance. A particular concern is sensitization in service. Aluminum is considered sensitized when a nearly continuous network of β phase forms along the grain boundaries. The β phase is anodic to the Al matrix, and, when exposed to sea water and sufficient loading, provides a clear pathway to stress corrosion cracking (SCC). The degree of β-phase precipitation is driven by a combination of time and elevated temperature. For over a decade, SCC of Al superstructures has plagued Navy ships. To address this issue, relevant technologies have been adopted, adapted, and developed to combat this issue. More specifically, the technology areas involve the detection of sensitization, the mitigation of SCC, and the replacement of corrupt materials. The technologies discussed herein a...

Survey of Detection, Mitigation, and Repair Technologies to Address Problems Caused by Sensitization of Al-Mg Alloys on Navy Ships

Reduction of Overwelding and Distortion for Naval Surface Combatants, Part 1: Optimized Weld Sizing for Lightweight Ship Structures

As high-strength thinner-steel implementation in ship designs increase, dimensional management becomes critical to control construction costs and schedule in ship production. In the U.S. shipbuilding industry, improvements to shipbuilding facilities and processing technology have not kept pace with the rate of change in ship design. Additionally, new designs using thinner steels are subject to legacy weld sizing criteria possibly leading to inappropriately sized welds on lightweight materials. These two factors result in widespread overwelding, causing severe plate deformation in naval vessels during construction and nonvalue added labor to correct as needed for fit-up tolerances. Historically, shear and fatigue strength data has been focused on the larger welds and thicker steel plates typical of the state of the practice when these legacy weld sizing criteria were developed. In order to optimize weld design and production in modern, lightweight naval surface vessels, there is a need to develop more accurate data about the performance of precision fillet welds for thin steels.

Reduction of overwelding and distortion for naval surface combatants. Part 2: Weld sizing effects on shear and fatigue performance

An evaluation of the relevance of the mass loss in ASTM G67 to the in-service stress corrosion cracking (SCC) performance of high magnesium aluminum alloys is needed to validate the mass loss requirements in ASTM B928/B928M. However, uniaxial SCC testing of thin gauge aluminum alloys in orientations other than short transverse (ST) cannot reliably predict SCC performance for in-service applications with an ST stress component. The objectives of this study were to identify an SCC test specimen and evaluate various exposure conditions. The suitability of U-Bend specimens (per ASTM G30) to study stress corrosion cracking was established using 5083-H321 material that was thermally treated to intentionally create a sensitized condition. The testing, which was conducted at NASA Kennedy Space Center Beach Corrosion Test Site (BCTS), demonstrates the relative severity of seacoast atmosphere, full seawater immersion, seawater spray zone, and tidal exposures. Results of this study will be used to select the environmental conditions for additional testing of 5xxx materials with varying degrees of intentional sensitization to validate the mass loss requirements specified in ASTM B928/B928M.

Development Of Test Specimens For Evaluating Scc Behavior Of Marine Aluminum Alloys And Assessment Of The Severity Of Various Marine Exposure Conditions

Catherine Wong

Papers

Survey of Detection, Mitigation, and Repair Technologies to Address Problems Caused by Sensitization of Al-Mg Alloys on Navy Ships

Reduction of Overwelding and Distortion for Naval Surface Combatants, Part 1: Optimized Weld Sizing for Lightweight Ship Structures

Reduction of overwelding and distortion for naval surface combatants. Part 2: Weld sizing effects on shear and fatigue performance

Development Of Test Specimens For Evaluating Scc Behavior Of Marine Aluminum Alloys And Assessment Of The Severity Of Various Marine Exposure Conditions