Abstract-The conventional stress wave signal interpretation in heat exchanger tube inspection is human dependent. The difficulties associated with accurate defect interpretations are skills and experiences of the inspector. Hence, in present study, alternative pattern recognition approach was proposed to interpret the presence of defect in carbon steel heat exchanger tubes SA179. Several high frequency stress wave signals propagated in the tubes due to impact are captured using Acoustic Emission method. In particular, one reference tube and two defective tubes were adopted. The signals were then clustered using the feature extraction algorithms. This paper tested two feature extraction algorithms namely Principal Component Analysis (PCA) and Auto-Regressive (AR). The pattern recognition results showed that the AR algorithm is more effective in defect identification. Good comparisons with the commonly global statistical analysis demonstrate the effective application of the present approach for defect detection. IndexTerms-Auto-regressive, pattern recognition, principal component analysis, stress wave.

supported by the decrease in dislocation density with increase in time and temperature, which is in-line with the Vickers micro-hardness results.

The automotive industry is the main consumer of dual-phase (DP) steels which have relatively impressive mechanical strength. DP steels are also known to have good ductility and load-bearing property because of their hard martensitic microstructure in soft ferrite grains. The main objective of this study is to determine the mechanical behaviour of DP steels with various martensite volume fractions. A heat treatment with an intermediate quenching procedure followed by three different intercritical temperatures is conducted to produce various ferrite–martensite containing DP steels with different martensite volume fractions (V_m). V_m affects the mechanical properties of steel, such as work hardening, ultimate tensile strength, yield strength and hardness. The results of the experiments conducted in this study prove that excellent work hardening and ductility are observed for DP steels with a low amount of martensite phase. Meanwhile, DP steels with high V_m exhibit high tensile strength and hardness with low ductility. Considère criterion is used to analyse the work hardening behaviour of DP steels. Results indicate that a one-stage work hardening takes place in DP steels; according to Considère criterion, instability strain or uniform elongation is also slightly increased by decreasing the martensite volume fraction or increasing the work hardening rate.