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New thermoset composite material made from cardanol-based resin blended with microfibrillar cellulose was compared to petroleum-based vinyl ester and glass-fiber-reinforced unsaturated polyester in terms of mechanical, thermal, rheological and surface properties of produced polymers and composites. The bio-sourced material was less resistant than the commercial vinyl ester but comparable to the unsaturated polyester resin. Microfibrillar cellulose increased the tensile strength and modulus but increased the resin viscosity and decreased the mixture homogeneity. The bio-sourced and commercial resins displayed similar hydrophobic behavior, and cellulose slightly decreased composite hydrophobicity. The glass transition temperature of the bio-sourced material was comparable to that of the unsaturated polyester. Thermal decompositions of composites and thermoset polymers were also similar. Cellulose and cardanol thus may be adequate as sustainable components in the composite materials industry.

The influence of the drilling parameters and the stacking sequence of flax/epoxy composite laminate on the cutting force and the damage induced were studied experimentally and numerically. Drilling tests were carried out based on full experimental design and the delamination at the entry and exit of the hole were quantified using an optical microscopy. Moreover, the damages at the wall of the hole were analyzed using scanning electron microscopy. Based on the experimental results, it was observed that the drilling forces and the machining quality are influenced on the one side by the spindle speed and feed and on the other side by the stacking sequence composite plate. In fact, the cutting forces recorded when drilling a composite plate with [90/0/90/0]2s is 30% higher to the one recorded when drilling a composite made with quasi-isotropic stacking sequence. A numerical model was developed in ABAQUS/Explicit using Hashin’s failure criteria in order to predict the cutting forces and the defects induced by the interaction of the drill and composite as a function of the machining parameters. The developed model has been validated at the macro-scale (thrust force) and the meso-scale (delamination at the entry and exit of the hole).

International audience; The three-dimensional printing of long fiber composites was developed in recent years, and the mechanical behavior of the printed composites requires further investigation. The joining of this type of material requires a hole; and with reference to the available literature, the bearing strength requires investigation. In this context, three manufacturing processes were used for hole generation: direct printing, conventional drilling, and abrasive waterjet drilling (AWJ). The holes obtained by these manufacturing processes were characterized using X-ray tomography and a roughness system. Open-hole quasi-static and fatigue tests were used to assess the mechanical behavior of hole manufacturing on the tensile sections. Single-shear bearing tests yielded the same trend as that observed with open holes, where conventional drilling demonstrated higher performance than the printed and AWJ specimens. The absence of delamination and higher drilling temperature sealed the surface, thus limiting the influence of voids.

Conventional milling during aircraft structural composite repair encourages defect generation and distortion, causing hindrance in milling depth control and thereby adversely affecting their mechanical behavior. Abrasive water jet (AWJ) milling can be an alternative to avoid these problems. In this study, carbon/epoxy laminates are milled using AWJ and machined surfaces are characterized at micro (surface texture) and macro (damage size) scales. Defects in the form of craters, ridges-valleys and broken fibers are identified and quantified. A new parameter “crater volume (Cv)” is proposed to quantify and qualify the machining quality in terms of induced damage. This introduces a novel approach to characterize the machined surface without ignoring the machining damage. Milled specimens with different damage levels are subjected to tensile and tension-tension fatigue tests instrumented with thermography and acoustic-emission transducers. Machined specimens with high Cv exhibited inferior fatigue behavior and X-ray tomography revealed that crack/fracture initiation occurred from the crater edges.

The aim of this work is to investigate the effects of wet/dry aging cycles on flax/epoxy composite properties for long-term structural applications. The mechanical performance of flax/epoxy exposed to wet/dry cycles during 104 days was evaluated. The physicochemical changes induced by wet/dry cycles were also studied. Unaged and cyclic aged samples were characterized by tensile test, X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and thermogravimetric analysis (TGA). The tensile test results showed good aging performance of this composite. FTIR chemical investigation revealed the disappearance of the characteristic peaks of the cyanoethylation treatment at the fiber/matrix interface during cyclic aging. TGA data showed an improvement in thermal properties of the composite after the hydrolysis of cyanoethyl group, as well as the increase of the crystallinity index, as measured from XRD during cyclic wet/dry aging. This explains the limitation of mechanical degradation of this composite despite the severe wetting-drying cycles aging conditions. The results also show the positive effects of the cyanoethylation fiber treatment on the long-term durability of flax/epoxy composite.

In many applications, metal gears have been replaced by plastic gears because of their functionality and cost advantages. Despite their many benefits, the intensive use of plastics and composites raises sustainability issues because of the depletion of non-renewable petroleum resources and the pollution that is generated. Thus, alternative ecological solutions for plastic gears are necessary; however, little is known regarding ecologically designed gears. In this study, we propose two types of innovative gear materials. The first is a semi-ecological polyethylene bio-composite gear reinforced with birch fibers, and the second is a fully bio-sourced natural polyethylene gear with birch fibers. This study is the first time such fully ecological composite-plastic gears have been tested. The tests record the evolution of the fatigue and temperature over time under various operating conditions. Furthermore, acoustic emission is used to assess the evolution of fatigue cracks. The results indicate that the fully ecological gears are feasible and offer an alternative to traditional materials, such as engineering plastics, likely at a lower cost.

A new natural fiber composite made of high density polyethylene (HDPE) and 40% wt of short birch fibers (SBF) was developed to replace polyamide (better known under its industrial name “Nylon”) in spur gear manufacturing. The effect of hygrothermal aging on quasi-static and fatigue bending behaviors of this new composite has been studied in this work. Once hygrothermal aging is completed, flexural quasi-static tests have been performed on aged specimens and results compared with those obtained from unaged specimens. It has been observed that hygrothermal aging has no significant effect on flexural mechanical properties of this composite. After characterization, bending fatigue tests have been conducted on aged specimens and results have been compared with those of unaged specimens. These fatigue tests show that hygrothermal aging decreases the high cycles fatigue strength (HCFS) of this composite. The cause of this fatigue durability decrease has been investigated using Fourier transform infrared spectroscopy (FT-IR), thermogravimetric analysis (TGA) and a scanning electron microscope (SEM). These tests show that the chemical composition and thermal behavior of this composite are not affected by hygrothermal aging. On the contrary, these tests show that damage mechanisms of this composite (HDPE/40% wt of SBF) are directly affected by this type of aging.

© The Author(s) 2018. This is the first study, to the authors' knowledge, to simultaneously perform a direct comparison of finite element analysis, strain gage measurements, and infrared thermography for stress analysis under both static and dynamics tensile loads of the classic geometry of a composite plate with a center hole. The plate was made from a carbon fiber-reinforced epoxy composite with dimensions of 250 mm length × 25 mm width × 2.2 mm thickness and a 5 mm diameter center hole. Using static tensile loads of 1000 N, 2000 N, and 3000 N, the plate Von Mises stress field was evaluated using strain gages versus finite element analysis. Using cyclic tensile loads of 1000 N and 1600 N at 5 Hz, the plate Von Mises stress field was assessed using strain gages versus infrared thermography. The strain gages versus finite element analysis line-of-best-fit showed poor agreement (slope = 2.1, R = 0.81), although the slope could easily be applied as a correction factor when comparing the two methods. The strain gages versus infrared thermography showed much better agreement (slope = 0.95, R = 0.91). Finite element analysis displayed a “butterfly” stress field around the hole with peaks of 73.5 MPa (at 1000 N), 147 MPa (at 2000 N), and 220.5 MPa (at 3000 N). Infrared thermography showed a “ring” of high stress around the hole with peaks of 74.8 MPa (at 1000 N) and 102.9 MPa (at 1600 N). All three methods showed similar relative trends for the carbon fiber-reinforced epoxy plate.

International audience; In this study, mechanical behavior and damage of thick laminated carbon/epoxy composite are investigated through static and fatigue three-point bending tests. In order to supply a maximum of information about the mechanical behavior of these materials, which have been little studied in the literature, and to provide an accurate description of the different mechanisms involved during their damage process, three non-destructive evaluation and monitoring techniques were used in this study. The acoustic emission for damage assessment, identification, and their threshold detection, the infrared thermography for fatigue damage evaluation and fatigue limit estimation and the digital image correlation for strain and displacement fields measurements.

Short flax fibers mats, unidirectional (UD) layers of flax yarns, and an assembly of these two, are used as reinforcements for an epoxy matrix composite. The tensile and flexural properties of the three different composites, in both longitudinal and transverse directions, were studied in order to highlight the effect of mat surface density, using two stacking sequences. A slight decrease of the measured longitudinal properties is observed when low levels of short fibers content are used. This is compensated by a significant decrease of the material variability, a significant increase of the transverse properties, and a favorable effect on the fracture behaviour of the tested specimens. Damage evolution is monitored using acoustic emission (AE) and the use of multivariable analysis of the collected data has given a clear description of the different damage modes, their evolution and their contribution to overall composite failure. Different damage behaviours are observed for the mats and UD samples. Most importantly their combination into a single reinforcement has a positive effect on damage type and evolution. The presence of short fibers in the composite reduces the crack propagation along the fibers/matrix interface, which reduces splitting and transforms the fracture surface from a serrated fracture surface to a flat and confined fracture surface.

A new natural fiber composite made of high density polyethylene (HDPE) and short birch fibers (SBF) was developed to replace high-performance thermoplastics (Polyamide) commonly used in gears manufacturing. 3-point flexural quasi-static tests were achieved on bending specimens to assess mechanical properties. Comparison between these results and those of polyamide (PA) and neat polyethylene has showed that the polyethylene reinforced with 40%wt of SBF presents tensile and flexural mechanical properties that are higher than those of the PA11 or the neat polyethylene. After static characterisation, fatigue tests were performed to determine e-N curves and the evolution of residual strength. Then, the fatigue behavior of the studied composite has been compared with that of PA66 and of ultra-high molecular weight polyethylene (UHMWPE). It has been noticed that polyethylene reinforced with 40%wt of SBF presents a high cycle fatigue strength (HCFS) that is more important than that of PA66 and UHMWPE. Consequently, the studied composite represents a good alternative to replace Nylon in spur gears manufacturing.

International audience; The main purpose of this study is to provide a thorough experimental investigation of fatigue damage mechanisms and evolution in thick carbon/epoxy laminate subjected to bending load. The use of X-ray computed tomography (CT) in this study has allowed the visualization of all damage present in the studied laminates, which made it possible to identify, quantify and locate them precisely and therefore, to identify the physical origin of residual strength decrease and acoustic emissions (AE). Furthermore, the results of the AE analysis have provided very valuable information about the nature and evolution of damage. However, the determination of the depth and size of internal damage was not possible with this technique. The displacement field measured by digital image correlation (DIC) made it possible to determine and monitor the strain field evolution during the experiments. The combination of the results of the three non-destructive techniques used in this work has allowed better characterization of fatigue damage evolution in the studied laminates, and provide a complete and accurate description of the different mechanisms involved during their damage process.

Natural-fiber-reinforced composites offer various advantages over synthetic composites, including low density, useful mechanical properties and environmental friendliness. In spite of the progress achieved in the field, the mechanical performance of these composite materials has yet to be fully characterized, particularly in terms of impact resistance. In this study, we measured the drop weight impact, Izod impact strength, hardness, tensile strength and elastic modulus of birch-fiber-reinforced HDPE obtained by injection molding. Drop weight impact energy absorbed was constant and independent of fiber content whereas impact strength was inversely proportional to fiber content. Material toughness decreased slightly at 40% fiber. The Shore D hardness of virgin HDPE increased from 50.6 at 0% fiber to 74.6 at 30% fiber. The improvement of the elastic modulus of a composite containing 40% fiber was 27.2% superior to that reported for similar material made by compression molding. The corresponding improvement in tensile strength was superior by 19.7%. Birch-fiber-reinforced HDPE could be an adequate alternative to technical polymers widely used in several industrial sectors.

In this study, the mechanical behavior of high-density polyethylene (HDPE) reinforced with short natural fiber was evaluated using a test bench designed to monitor the high-cycle bending-fatigue characteristics of gear teeth. High-resolution imaging and acoustic emission (AE) were used to document crack initiation and propagation against the number of cycles for all specimens. Fatigue versus number of cycles was modeled using S–N curves, damage indices and a linearized Weibull distribution. Correlations between the variables are discussed and compared with published data. Crack progression, residual load, and AE show consistent results that track the progressive damage to the material.

This work studies the long-term hygrothermal (HT) aging effect on the fatigue behavior of a flax/epoxy bio-composite arranged in [02/902/±45]S lay-ups. The effect of aging on static tensile mechanical properties was first investigated. Tension–tension fatigue tests were also performed for both unaged and aged samples. The distribution of fatigue life for both unaged and aged sample was determined. The evolution of fatigue properties was also investigated. Fatigue tests were coupled with acoustic emission (AE) for a better understanding of how these composites react to fatigue loading in wet environmental conditions. Static tests show that water absorption affects negatively the elastic properties of this material. S–N curves show a good performance in fatigue strength of unaged samples. This performance dropped significantly with HT aging. The analysis of stress–strain hysteresis loops allowed to determine the minimal strain such as the desirable fatigue properties to explain fatigue damage evolution for single stress component. Hwang–Han’s model based on minimal strain was also used to predict the fatigue damage of the tested flax/epoxy composites. Principal component analysis enabled to separate the fatigue damage evolution of unaged and aged samples. AE results confirmed that the damage evolution of both samples is not the same. AE analyses were permitted to identify the growing fiber/matrix debonding and pull-out mechanism in the unaged samples. Correlation between AE and scanning electron microscope observations enabled the identification of several damage mechanisms and their evolution during the fatigue tests.

Most design approaches use the experimental elastic modulus as input variable to describe the material properties. In most cases the uncertainty and the variability of the modulus are neglected. In the worst case this can lead to bad estimations of the material performance and more iterations to the final solution. The purpose of this work is to reconcile the Young's modulus of three configurations ([0]10, [0]20 and [±45]10) of flax–epoxy composites obtained by different techniques including acoustic impulse, tensile and bending tests, according to ISO and ASTM standards. Results obtained with these techniques all show different levels of variability in Young's modulus values. A fuzzy logic model is used to obtain a simplified view of linguistic variables representing the modulus of elasticity and to reconcile different modules by including the uncertainty inherent to the different measuring techniques. Results have shown a strong potential for fuzzy logic to reconcile the disparity of Young modulus of natural fiber composites. Keywords: Natural fiber composites, Tensile test, Bending test, Impulse excitation technique, Fuzzy logic

There is a need to correctly dimension gears for an application with an understanding of how the gear will deteriorate until final failure. However, this task has been difficult because engineers must consider the complexity of gear meshing phenomena combined with the gear material-specific properties and application particularities to determine the critical failure and maintenance points. This article provides a review of the multiple damage modes of plastic gears, including both general and plastic gear-exclusive modes. This article reviews the different branches of the damage problem, performs a combined solution of finite element analysis (FEA) and validated analytical equations for plastic gears. With this knowledge, a unique system of analysis of gear utilization perspectives that evaluates all possible damaging processes is built. By applying a range of normal loads on a plastic gear, it was verified that the damage mode depends highly on the applied load. The identification of the proper damage mode allows preventive actions to be taken because the limits of plastic gears and the optimal usage are identified. With this damage modeling strategy, the designer can skip several steps in reaching a decision regarding plastic gear applicability. This synthesis represents significant progress for plastic gear damage modeling because the major factors of plastic gear functioning and the damage factors are observed.

In the aeronautical industry, many critical components are made of high-strength steels. These steels have high tensile strength but are sensitive to corrosion and to the hydrogen embrittlement phenomenon. This study examines how acoustic emission could be used to detect hydrogen embrittlement of high-strength steels and reduce the duration of the standard test. Acoustic emission (AE) was coupled with sustained load testing at 75% of the material fracture stress for 200 h as prescribed in ASTM standard F519. Tensile strength tests were also conducted to determine the mechanical characteristics and acoustic signature of the mechanisms of damage that progress to material fracture. The results show that the time required for sustained load tests can be shortened, based on the emission of acoustic events by the hydrogen-embrittled test coupons from the beginning of the test and after certain lengths of time. Scanning electron microscopy imaging of the fracture surfaces showed a very good correlation with the recorded acoustic event signatures.

International audience; Natural fibers have enormous potential and offer many advantages. However, the lack of confidence in their structural performance has limited their wider adoption. Among concerns, include susceptibility to higher water absorption. The aim of this paper is to characterize the impact of the water absorption of jute/epoxy composite material using a new approach. This material has a potential to be used in automobile industries (door panels, dashboards, etc.) and in the civil engineering (skins of the sandwich panels in the building). The method of characterization used is original and based on the impulse excitation approach. The mechanical properties identified are correlated to those obtained by classical methods of characterization such as: three points bending and shear tests. Results show clearly that the rate of water absorption decreases physical (resonant frequency) and mechanical properties (Young’s modulus) of jute/epoxy laminate. At the mass saturation, we recorded a decrease in the proper frequency around 10%, and the Young’s modulus in this case loses 28% to 38% of its initial value. In addition, water bath temperature had an important impact on the coefficient of diffusion as well as on the degradation of mechanical properties.

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. POLYM. COMPOS., 2015. © 2015 Society of Plastics Engineers

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 of damage 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 long-term applications.

One of the strongest aluminum alloy is AA7075; it has a yield strength of 350 MPa in the T73 heat-treated state, which is 50% stronger than construction steels. The alloy contains a high mass fraction of alloying elements, but no silicon; therefore it is not easily cast into complex shapes by traditional foundry processes since it is prone to shrinkage, hot tearing and has low fluidity. However, the high pressure vacuum die casting (HPVDC) process uses high metal velocities to fill the mold cavity and applies a pressure during solidification to feed shrinkage, which could facilitate the production defect free castings. Casting AA7075 alloy would be highly beneficial to produce complex shapes and reduce assembly steps. This work will focus on AA7075 production by HPDVC process and the effect of grain refiner on the casting defects and mechanical properties of cast AA7075. It is well known that castings endurance limit is highly affected by defects (porosity, oxides, cold shuts, etc.). In this work, the main objective is to study the impact of the HPVDC process on the endurance limit of AA7075, as well as the effect of grain refiner (TiB2) in reducing the casting defects and enhancing the endurance limit of the cast alloy. The endurance limit will be studied through uniaxial tension-tension fatigue tests on T73 heat-treated AA7075 castings. The microstructures of AA7075 alloy cast with and without TiB2 was observed by optical and electron microscopy. Stress controlled fatigue testing up to 106 cycles will be used to trace the Wholer curves and study the effect of TiB2 on the endurance limit.

International audience; The influence of the machining quality on the mechanical behavior of CFRP composites is yet not fully understood. There are only few works in the literature that have investigated the effect of the machining quality on CFRP. In fact, most of these works focus only on conventional machining such as axial or orbital drilling. The aim of this paper is to examine the influence of two machining processes namely conventional machining (CM) and abrasive water jet machining (AWJM) on the mechanical behavior of composite plates under cyclic loading. For this purpose, an experimental study using several composite plates drilled with a cutting tool and an abrasive water jet machining was carried out. In order to study the impact of the process of machining on the mechanical behavior, thermographic infrared testing and fatigue cyclic tests were performed to assess temperature evolutions, stiffness degradation, and the damage evolution in these plates. Fatigue testing results have shown that the damage accumulation in specimens drilled with CM process was higher than the AWJM specimens. Furthermore, the endurance limit for a composite plate drilled with CM was approximately 10% inferior compared to specimens drilled with AWJM. This difference can be related to the initial surface integrity after machining induced by the difference in the mechanism of material's removal between the two processes used. Key words: E. Machining, C. Damage mechanics; D. Mechanical testing, E. Thermal analysis

The late Quaternary sequences of north-eastern Algeria composed of alternating dark and light layers, which are rich in molluscan fauna, could correspond to synchronous environmental phases. The facies variations of the Morsott Region deposits were systematically sampled as part of a sedimentological and malacological study in order to establish a palaeoenvironmental and climatic reconstruction of the late Quaternary. The alternation of sandy clayey silts levels, which contain abundant molluscan hygrophilous organisms, indicates an isostasis cycle followed, at the top, by a succession of rhexistasis and biostasis cycles. The molluscan record shows a dominant succession of xerophilous organisms in relation to the hygrophilous organisms. The faunistic richness in the fine levels is linked to sub-humid periods where the region has suffered numerous floods. The reduction in the number of species in the coarse levels comes is likely due to desiccation when the climate was semi-arid. This study is new in Algeria and will provide an insight into climatic changes. Further research will be required in order to understand the fluvial dynamics during the Quaternary.

Etching patterns displayed on the surfaces of near-alpha titanium forgings (alloy IMI834) were quantified in terms of sizes and orientations using a two-dimensional (2-D) autocorrelation method. These patterns, which can be associated with local variations of microstructure and further related to regions of specific crystallographic orientations, are known to play a significant role in fatigue and dwell fatigue life predictions. It is then necessary to quantify their dimensions in a manufactured part in order to build a better statistical approach for life prediction in titanium forgings. These distributions of macroregion size and shape were examined on forging cross sections. A data analysis methodology based on a 2-D autocorrelation was used to process sample image data and quantify the macroregion characteristics. The results are more precise than those obtained using a mean linear intercept (MLI) method and additional useful information can be gathered., available, unlimited, public

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.

An analytical model based on cumulative damage has been used for predicting the damage evolution in composite materials. The model is verified with experimental data from a carbon/epoxy composite fatigued under tension–tension load. Fatigue tests of specimens have been monitored with an infra-red thermography system. By analysing the temperature of the external surface during the application of cyclic loading, it is possible to evaluate the damage evolution. The model agrees well with the experimental data, and it can be used to predict the evolution of damage in composites.

A non-contact measurement method, namely electronic speckle pattern interferometer (ESPI), was used to investigate the tensile strain field of a composites plate in the presence of stress concentrations caused by a geometrical defect consisting of circular hole. ESPI uses the principle of 3D speckle interferometry to measure the deformation and contour of the measuring field with sub-micrometer accuracy. The ESPI technique clearly revealed the strain concentrations near the singularity. The experimental results are compared with the predictions of a theoretical model previously developed by Lekhnitskii's and a finite element study.

This study addresses cumulative damage and its evolution during the cold dwell fatigue of a near-α titanium alloy. An experimental study was undertaken to examine the evolution of life, strain, strength and damage of 13 titanium IMI 834 samples cut from a single disk forging. The samples were tested in the same dwell-fatigue loading conditions. In the dwell phase, the load is maintained at 80% of ultimate tensile strength (824 MPa, 90% of yield strength) for 30 s. The secant Young’s modulus and inelastic strain at minimum load were measured in order to document the evolution of the irreversible damage against the number of cycles for all specimens. Experimental observations show significant differences in dwell-fatigue life and damage behavior. This mechanical analysis and an analysis of the cumulative Weibull reliability distribution suggest a bimodal dwell-fatigue failure process. Some features of the mechanical behavior can be used to sort the samples according to each of the two failure modes and improve the reliability of the fatigue test campaign.

International audience; Titanium alloys are known to have texture heterogeneities, i.e. regions much larger than the grain dimensions, where the local orientation distribution of the grains differs from one region to the next. The electron backscattering diffraction (EBSD) technique is the method of choice to characterize these macro regions, which are called macrozones. Qualitatively, the images obtained by EBSD show that these macrozones may be larger or smaller, elongated or equiaxed. However, often no well-defined boundaries are observed between the macrozones and it is very hard to obtain objective and quantitative estimates of the macrozone dimensions from these data. In the present work, we present a novel, non-destructive ultrasonic technique that provides objective and quantitative characteristic dimensions of the macrozones. The obtained dimensions are based on the spatial autocorrelation function of fluctuations in the sound velocity. Thus, a pragmatic definition of macrozone dimensions naturally arises from the ultrasonic measurement. This paper has three objectives: 1) to disclose the novel, non-destructive ultrasonic technique to measure macrozone dimensions, 2) to propose a quantitative and objective definition of macrozone dimensions adapted to and arising from the ultrasonic measurement, and which is also applicable to the orientation data obtained by EBSD, and 3) to compare the macrozone dimensions obtained using the two techniques on two samples of the near-alpha titanium alloy IMI834. In addition, it was observed that macrozones may present a semi-periodical arrangement.

The characterisation of composite plates used in structural work in the field of aeronautics is approached by associating ultrasound and speckle interferometry measurements. The reduced thickness of the specimens does not allow for gauge instrumentation to measure out-of plane deformation. A system was therefore used which makes it possible to obtain the cartography of the deformations in and out of-plane. This paper describes an application of electronic speckle interferometry in the measurement through thickness deformation in composites.