Average grain size evaluation using scattering-induced attenuation of coda waves.

Grain size is one of the key microstructural factors affecting the mechanical properties of polycrystalline metal materials. In this study, a novel method for grain size evaluation using ultrasonic coda waves is proposed. Different from conventional bulk wave methods that require a point-by-point scanning of the structure, the proposed method allows for a rapid evaluation of the average grain size of the whole part from a single inspection location using one-pass testing data.

Spatial and directional characterization of wire and arc additive manufactured aluminum alloy using phased array ultrasonic backscattering method.

Pores, grains, or textures can collectively cause microstructural inhomogeneity and anisotropy in metallic materials fabricated by additive manufacturing. In this study, a phased array ultrasonic method is developed to characterize the inhomogeneity and anisotropy of wire and arc additively manufactured components by performing both beams focusing and steering. Two backscattering features, i.

An Engineering Prediction Model for Stress Relaxation of Polymer Composites at Multiple Temperatures.

This study develops an engineering prediction model for stress relaxation of polymer composites, allowing the prediction of stress relaxation behaviour under a constant strain, over a range of temperatures. The model is based on the basic assumption that in the stress relaxation process the reversible strain is transformed to irreversible strain continuously. A strain-hardening model is proposed to incorporate nonlinear elastic behaviour, and a creep rate model is used to describe the irreversible deformation in the process.

A Phenomenological Primary-Secondary-Tertiary Creep Model for Polymer-Bonded Composite Materials.

This study develops a unified phenomenological creep model for polymer-bonded composite materials, allowing for predicting the creep behavior in the three creep stages, namely the primary, the secondary, and the tertiary stages under sustained compressive stresses. Creep testing is performed using material specimens under several conditions with a temperature range of 20 °C-50 °C and a compressive stress range of 15 MPa-25 MPa. The testing data reveal that the strain rate-time response exhibits the transient, steady, and unstable stages under each of the testing conditions.

A General Temperature-Dependent Stress-Strain Constitutive Model for Polymer-Bonded Composite Materials.

This study develops a general temperature-dependent stress-strain constitutive model for polymer-bonded composite materials, allowing for the prediction of deformation behaviors under tension and compression in the testing temperature range. Laboratory testing of the material specimens in uniaxial tension and compression at multiple temperatures ranging from -40 ∘C to 75 ∘C is performed. The testing data reveal that the stress-strain response can be divided into two general regimes, namely, a short elastic part followed by the plastic part; therefore, the Ramberg-Osgood relationship is proposed to build the stress-strain constitutive model at a single temperature.

Maximum Entropy Approach to Reliability of Multi-Component Systems with Non-Repairable or Repairable Components.

The degradation and recovery processes are multi-scale phenomena in many physical, engineering, biological, and social systems, and determine the aging of the entire system. Therefore, understanding the interplay between the two processes at the component level is the key to evaluate the reliability of the system. Based on the principle of maximum entropy, an approach is proposed to model and infer the processes at the component level, and is applied to repairable and non-repairable systems.

Three-dimensional damage quantification of low velocity impact damage in thin composite plates using phased-array ultrasound.

The evaluation of internal damage in multilayered composite materials is of great importance for high reliability-demanding applications, and remains a challenge due to the complex failure modes and mechanism of composite materials. This study presents a volumetric method of three-dimensional size quantification and prediction for low velocity impact damage in thin composite plates using phased-array ultrasound. A set of low velocity impact damages are induced in thin carbon fiber/epoxy resin matrix composite plates using quasi-static indentation tests.

Maximum entropy approach to reliability.

The aging process is a common phenomenon in engineering, biological, and physical systems. The hazard rate function, which characterizes the aging process, is a fundamental quantity in the disciplines of reliability, failure, and risk analysis. However, it is difficult to determine the entire hazard function accurately with limited observation data when the degradation mechanism is not fully understood.

A model assessment method for predicting structural fatigue life using Lamb waves.

This paper presents a study on model assessment for predicting structural fatigue life using Lamb waves. Lamb wave coupon testing is performed for model development. Three damage sensitive features, namely normalized energy, phase change, and correlation coefficient are extracted from Lamb wave data and are used to quantify the crack size.

A Fatigue Crack Size Evaluation Method Based on Lamb Wave Simulation and Limited Experimental Data.

This paper presents a systematic and general method for Lamb wave-based crack size quantification using finite element simulations and Bayesian updating. The method consists of construction of a baseline quantification model using finite element simulation data and Bayesian updating with limited Lamb wave data from target structure. The baseline model correlates two proposed damage sensitive features, namely the normalized amplitude and phase change, with the crack length through a response surface model.

An Integrated Health Monitoring Method for Structural Fatigue Life Evaluation Using Limited Sensor Data.

A general framework for structural fatigue life evaluation under fatigue cyclic loading using limited sensor data is proposed in this paper. First, limited sensor data are measured from various sensors which are preset on the complex structure. Then the strain data at remote spots are used to obtain the strain responses at critical spots by the strain/stress reconstruction method based on empirical mode decomposition (REMD method).

Lamb Wave Damage Quantification Using GA-Based LS-SVM.

Lamb waves have been reported to be an efficient tool for non-destructive evaluations (NDE) for various application scenarios. However, accurate and reliable damage quantification using the Lamb wave method is still a practical challenge, due to the complex underlying mechanism of Lamb wave propagation and damage detection. This paper presents a Lamb wave damage quantification method using a least square support vector machine (LS-SVM) and a genetic algorithm (GA).

Time Domain Strain/Stress Reconstruction Based on Empirical Mode Decomposition: Numerical Study and Experimental Validation.

Structural health monitoring has been studied by a number of researchers as well as various industries to keep up with the increasing demand for preventive maintenance routines. This work presents a novel method for reconstruct prompt, informed strain/stress responses at the hot spots of the structures based on strain measurements at remote locations. The structural responses measured from usage monitoring system at available locations are decomposed into modal responses using empirical mode decomposition.

A time-domain synthetic aperture ultrasound imaging method for material flaw quantification with validations on small-scale artificial and natural flaws.

A direct time-domain reconstruction and sizing method of synthetic aperture focusing technique (SAFT) is developed to improve the spatial resolution and sizing accuracy for phased-array ultrasonic inspections. The basic idea of the reconstruction algorithm is to coherently superimpose multiple A-scan measurements, incorporating the phase information of the sampling points. The algorithm involves data mapping and in-phase summation according to time-of-flight (TOF).

Material damage diagnosis and characterization for turbine rotors using three-dimensional adaptive ultrasonic NDE data reconstruction techniques.

Damage diagnosis for turbine rotors plays an essential role in power plant management. Ultrasonic non-destructive examinations (NDEs) have increasingly been utilized as an effective tool to provide comprehensive information for damage diagnosis. This study presents a general methodology of damage diagnosis for turbine rotors using three-dimensional adaptive ultrasonic NDE data reconstruction techniques.