No abstract

No abstract

International audienceThis paper aims at studying fatigue damage behavior of injection molded 30 wt% short glass fiber reinforced polyamide-66 composite (PA66/GF30). The evolution of dynamic modulus, hysteresis area, cyclic creep and temperature during fatigue tests were analyzed and discussed. Damage analyses by X-ray micro-computed tomography (lCT) technique on interrupted fatigue tests at several percentages of total fatigue life were performed to further understand the damage mechanisms and evolution during fatigue loading. It can be observed that experimental results related to the evolution of dynamic modulus, strain, temperature and energy dissipation are important and consistently complement each other for damage evaluation of PA66/GF30. During fatigue loading, diffuse damage occurs over the entire specimen though the damage does not necessarily exhibit the same level between different locations inside the specimen. The lCT analysis of voids characteristics demonstrates that the damage continuously increases during fatigue loading. The damage is developed notably along fiber interface in the form of fiber/matrix interfacial debonding

is an open access repository that collects the work of Arts et Métiers ParisTech researchers and makes it freely available over the web where possible. b s t r a c tDamage mechanisms of injection molded polyamide-66/short glass fiber 30 wt% composite (PA66/GF30) were analyzed using in situ SEM mechanical tests on specimens conditioned under three relative humidity contents (RH = 0%, 50% and 100%). The validity of these in situ analyses was confirmed by Xray micro-computed tomography (lCT) observations on tensile loaded specimens. Experimental results demonstrated that relative humidity (RH) conditions influence strongly the damage level and damage mechanisms. Indeed, for specimen with RH = 0%, damage initiation occurs at significantly higher load level than those in RH = 50% and RH = 100% specimens. The higher relative humidity condition also results in higher damage level. Damage chronologies have been proposed as damage initiation in the form of fiber-matrix debonding occurs at fiber ends and more generally at locations where fibers are close to each other due to the generation of local stress concentration (for all studied RH contents), and first fiber breakages occur (RH = 0%). These debonded zones further propagate through fiber-matrix interface (for all studied RH contents), and new fiber breakages develop (RH = 0%). At high relative flexural stress, matrix microcracks appear and grow regardless the RH contents. For RH = 100%, these microcracks are also accompanied by many matrix deformation bands. Subsequently, they lead to the damage accumulation and then to the final failure.

The current work deals with periodic thermomechanical composite media, in which the material constituents are considered to obey the generalized standard materials laws. The aim is to provide a proper homogenization framework that takes into account both the equilibrium and the thermodynamics laws in microscale and macroscale levels. The study is based on the asymptotic expansion homogenization technique, which permits to deduce useful results about the general structure of microscale and macroscale energy potentials and constitutive laws. The paper also proposes an incremental, linearized formulation that allows to identify suitable thermomechanical tangent moduli for the macroscale problem. The capabilities of this framework are illustrated with numerical examples on multilayered composites.

Following their discovery in the early 60's, there has been a continuous quest for ways to take advantage of the extraordinary properties of shape memory alloys (SMAs). These intermetallic alloys can be extremely compliant while retaining the strength of metals and can convert thermal energy to mechanical work. The unique properties of SMAs result from a reversible difussionless solid-to-solid phase transformation from austenite to martensite. The integration of SMAs into composite structures has resulted in many benefits, which include actuation, vibration control, damping, sensing, and selfhealing. However, despite substantial research in this area, a comparable adoption of SMA composites by industry has not yet been realized. This discrepancy between academic research and commercial interest is largely associated with the material complexity that includes strong thermomechanical coupling, large inelastic deformations, and variable thermoelastic properties. Nonetheless, as SMAs are becoming increasingly accepted in engineering applications, a similar trend for SMA composites is expected in aerospace, automotive, and energy conversion and storage related applications. In an effort to aid in this endeavor, a comprehensive overview of advances with regard to SMA composites and devices utilizing them is pursued in this paper. Emphasis is placed on identifying the characteristic responses and properties of these material systems as well as on comparing the various modeling methodologies for describing their response. Furthermore, the paper concludes with a discussion of future research efforts that may have the greatest impact on promoting the development of SMA composites and their implementation in multifunctional structures.

Abstract. This article reports on an ESF S3T EUROCORES sponsored networking activity called Roundrobin SMA modeling organized with the aim to compare capabilities of various thermomechanical models of shape memory alloys capable to simulate their functional responses for applications in smart engineering structures. Five sets of experimental data were measured in thermomechanical tests on thin NiTi filament in tension, torsion and combined tension/torsion. The data were provided to six teams developing advanced SMA models to perform appropriate simulations. Simulation results obtained by individual teams were compared with experimental results and presented on a dedicated Roundrobin SMA modeling website. The evaluation of the activity in terms of the assessment of the capability of individual models to deal with specific features of the experimentally measured SMA thermomechanical responses is provided in this article.

HAL is a multidisciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L'archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.