Dwell fatigue life dispersion of a near alpha titanium alloy

Early failure during dwell-fatigue of titanium alloys is a research of interest as it directly drives the in-service life of critical parts in turbines. A study was undertaken to examine the evolution of life and strain in six specimens made of near-alpha titanium alloy (IMI 834) during dwell-fatigue loading conditions. The strain accumulation in dwell-fatigue test for one sample was significantly different. This specimen presents a different ultrasonic response from that of the other specimens, that is ultrasonic measurements reveal a different macro-texture for this sample. When this specimen is excluded, it is found that ultrasonic speed correlates well with dwell-fatigue life for the remaining samples. This paper evaluates the usefulness of ultrasound waves to predict the strain and the dwellfatigue life of a titanium alloy.NRC publication: Ye

Development of novel green and biocomposite materials: Tensile and flexural properties and damage analysis using acoustic emission

A new green composite made of natural polyethylene (NPE) has never been produced using short birch fibers and compared with others biocomposites with matrices of linear low-density polyethylene (LLDPE) and high-density polyethylene (HDPE). Versions with and without a coupling agent (CA) in fiber ratios of 10, 20, 30 and 40 wt% were produced. Tensile and 3-point flexural tests were conducted to measure the mechanical properties of the composites, and acoustic-emission testing was used to measure the evolution ofdamage caused by irreversible changes in the materials in correlation with an analysis of the damage modes. It was concluded that the extent of the damage and the contribution of each damage mode depend on the material, the test performed and, especially the presence of a CA. The results prove that the choice of composite for a particular application must be a judicious one and should consider not only the mechanical properties but also the damage processes of the composite, which may be crucial for longterm applications

Damage Characterization of Bio and Green Polyethylene–Birch Composites under Creep and Cyclic Testing with Multivariable Acoustic Emissions

Despite the knowledge gained in recent years regarding the use of acoustic emissions (AEs) in ecologically friendly, natural fiber-reinforced composites (including certain composites with bio-sourced matrices), there is still a knowledge gap in the understanding of the difference in damage behavior between green and biocomposites. Thus, this article investigates the behavior of two comparable green and biocomposites with tests that better reflect real-life applications, i.e., load-unloading and creep testing, to determine the evolution of the damage process. Comparing the mechanical results with the AE, it can be concluded that the addition of a coupling agent (CA) markedly reduced the ratio of AE damage to mechanical damage. CA had an extremely beneficial effect on green composites because the Kaiser effect was dominant during cyclic testing. During the creep tests, the use of a CA also avoided the transition to new damaging phases in both composites. The long-term applications of PE green material must be chosen carefully because bio and green composites with similar properties exhibited different damage processes in tests such as cycling and creep that could not be previously understood using only monotonic testing

Hygrothermal effect on moisture kinetics and mechanical properties of hemp/polypropylene composite: experimental and numerical studies

The exposition of thermoplastic composites reinforced with natural fibers to moisture and heat is likely to lower their mechanical properties and restrain their use in the design of parts. The present work is focussed on investigating the effects of hygrothermal aging on the mechanical behaviour of injected polypropylene reinforced with short hemp fibers. Moreover, the kinetic of isothermal moisture absorption has been studied for four immersion temperatures. The experimental results show that the time taken to reach saturation decreases significantly with increase in immersion temperature. These tests also reveal that moisture absorption in this type of materials does not follow Fick's law. Thus, a new model is proposed to predict this behaviour by the use of a variable coefficient of diffusion. This model is implemented using both analytical and finite element analysis (FEA) approaches. The results obtained with this new model show a very good correlation between experimental, analytical, and FEA absorption curves

Approches analytique et expérimentale de l'endommagement par fatigue d'un composite carbone/epoxy

TOULOUSE3-BU Sciences (315552104) / SudocTARBES-ENIT (654402301) / SudocSudocFranceF

Artificial Neural Network Approach for Assessing Mechanical Properties and Impact Performance of Natural-Fiber Composites Exposed to UV Radiation

Amidst escalating environmental concerns, short natural-fiber thermoplastic (SNFT) biocomposites have emerged as sustainable materials for the eco-friendly production of mechanical components. However, their limited durability has prompted research into the experimental evaluation of the deterioration of the mechanical characteristics of SNFT biocomposites, particularly under the influence of ultraviolet rays. However, conducting tests to evaluate the mechanical properties can be time-consuming and expensive. In this study, an artificial neural network (ANN) model was employed to predict the mechanical properties (tensile strength) and the impact performance (resistance and absorbed energy) of polypropylene reinforced with 30 wt.% short flax or wood pine fibers (referred to as PP30-F or PP30-P, respectively). Eight parameters were collected from experimental studies. The ANN input parameters comprised nondestructive test results, including mass, hardness, roughness, and natural frequencies, while the output parameters were the tensile strength, the maximum impact load, and absorbed energy. The model was developed using the ANN toolbox in MATLAB. The linear coefficient of correlation and mean squared error were selected as the metrics for evaluating the performance function and accuracy of the ANN model. They calculate the relationship and the average squared difference between the predicted and actual values. The data analysis conducted by the models demonstrated exceptional predictive capability, achieving an accuracy rate exceeding 96%, which was deemed satisfactory. For both the PP30-F and PP30-P biocomposites, the ANN predictions deviated from the experimental data by 3, 5, and 6% with regard to the impact load, absorbed energy, and tensile strength, respectively

The Effects of Lignin on the Thermal and Morphological Properties and Damage Mechanisms after UV Irradiation of Polypropylene Biocomposites Reinforced with Flax and Pine Fibres: Acoustic Emission Analysis

This study investigates the impact of lignin on the durability and performance of polypropylene-based biocomposites (PP–flax and PP–pine) under environmental stresses such as UV radiation and moisture. The findings indicate that pine fibres, with their higher lignin content, are significantly more resistant to thermal degradation than flax fibres. Differential scanning calorimetry (DSC) showed that lignin influences crystallinity and melting temperatures across the composites, with variations corresponding to fibre type. Acoustic emissions analysis revealed that increasing the lignin content in pine fibres effectively reduces surface microcracks under UV exposure. Overall, these results underscore the importance of fibre composition in improving the performance and longevity of biocomposites, making them better suited for durable construction applications

The influence of the hole-generation process on fatigue response of open-hole and assembled titanium samples

International audienc

Macro texture regions in bimodal titanium forgings quantified by 2D autocorrelation method

Peer reviewed: YesNRC publication: Ye