Methodology
CHAPTER THREE
METHODOLOGY
3.1 Introduction
This chapter presents the research methods that were used to carry out the study. It covered the material and sample preparation, control variables, Mechanical Testing – Cyclic Loading, Corrosion Testing, Analysis of Microstructure and Crack Propagation, Data analysis and Interpretation and Conclusion.
3.1 Materials and Sample Preparation
The researcher will Select two metals that are commonly used in industry and have contrasting properties, such as stainless steel and carbon steel, to create dissimilar metal welds.
The researcher will Prepare welds between the selected metals using a standardized welding process, such as Gas Tungsten Arc Welding (GTAW) or Friction Stir Welding (FSW). Ensure that welds are made under controlled conditions to maintain consistency across samples. Cut the welded plates into samples with identical dimensions according to ASTM standards (e.g., ASTM E466 for fatigue testing) for ease of testing and consistency.
3.2 Control Variables
To isolate the effects of cyclic loading and corrosive environment, control variables such as weld heat input, welding speed, and cooling rate during welding.
Independent Variables
Cyclic load frequency, load amplitude, type and concentration of corrosive medium.
Dependent Variables
Fatigue life, crack initiation and propagation rate, and corrosion rate.
3.3 Mechanical Testing – Cyclic Loading
Conduct fatigue testing on the samples to evaluate the performance under cyclic loading. Use a servo-hydraulic testing machine to apply cyclic loads at different stress ratios (e.g., R = 0.1 and R = -1) and frequencies (e.g., 5 Hz to 20 Hz). Record the number of cycles to failure for each sample, noting variations based on weld location, material composition, and cyclic loading parameters.
3.4. Corrosion Testing
Expose samples to a controlled corrosive environment, such as a 3.5% NaCl solution, to simulate marine conditions. Alternatively, use sulfuric acid or another solution to simulate industrial corrosive environments. Perform electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization tests to analyze corrosion behavior.
3.4.1 Exposure Time
Vary the exposure time to analyze short-term and long-term corrosion effects on weld integrity and fatigue life.
3.5 Analysis of Microstructure and Crack Propagation
Use optical microscopy (OM) and scanning electron microscopy (SEM) to examine the microstructure of the welded joints, particularly focusing on grain structure, phase boundaries, and potential defects.
3.5.1 Fractography
After testing, use SEM to examine fracture surfaces and identify crack initiation sites and modes of crack propagation.
3.5.2 Crack Growth Rate
Use an optical microscope to track crack growth under cyclic loading, measuring the crack growth rate to assess the weld’s resistance to fatigue.
3.6 Data Analysis
The researcher will use statistical methods, such as analysis of variance (ANOVA), to analyze the impact of various loading conditions and corrosive environments on fatigue life and corrosion resistance.
The researcher will also carry out comparative Analysis to Compare the fatigue life and corrosion rate of dissimilar metal welds against similar metal welds as a benchmark.
3.7 Interpretation and Conclusion
The researcher will Interpret the results to assess how dissimilar metal welds perform under combined cyclic loading and corrosive conditions.
Identify trends and factors influencing fatigue life and corrosion resistance, concluding with practical recommendations for the application and improvement of dissimilar metal welds in relevant industries.
