Effects of hot-wet storage aging, CNT-integration and damping layer interposition on static and fatigue interlaminar shear response of a UD Graphite/Epoxy material system

2020 ◽  
Vol 25 ◽  
pp. 101296
Author(s):  
Theofanis S. Plagianakos ◽  
Kirsa Muñoz ◽  
Stylianos Strapatsakis ◽  
Maria del Mar Fernandez ◽  
Miguel Jimenez ◽  
...  
2020 ◽  
Vol 224 ◽  
pp. 106761 ◽  
Author(s):  
Theofanis S. Plagianakos ◽  
Kirsa Muñoz ◽  
Gerard Guillamet ◽  
Vasileios Prentzias ◽  
Adrià Quintanas-Corominas ◽  
...  

2020 ◽  
Vol 29 ◽  
pp. 096369351989500
Author(s):  
Boling He

Considering the fact that the foundation data for a new X850 ± IM190 carbon/epoxy material system adopted in commercial aircraft industry are extremely scarce in the literature, an in-plane, static tensile experiment was carried out to investigate the bearing performance of double-lap, single-bolt joints in X850 ± IM190 carbon fiber-reinforced polymer (CFRP) composites. The effects of ply ratio, 0° layers’ combination percentage, bolt diameter, and curing method were considered. Then, special attention was paid to determine the design parameters of X850 ± IM190 CFRP bolted joints, such as tensile strength of un-notched laminate and stress concentration relief factor. Based on these design parameters, an efficient semianalytical approach was established to obtain the ultimate bearing strength of the joints. The failure prediction exhibited excellent agreement with the experimental data. These results will play an important role in design and strength evaluation of X850 ± IM190 CFRP bolted joints.


2017 ◽  
Vol 52 (12) ◽  
pp. 1699-1708 ◽  
Author(s):  
Sung Kyu Ha ◽  
Carlos Alberto Cimini

The objective of this paper is to unveil the background theory behind the universal master ply assumption, based on the invariant approach, to describe ply elastic properties. It was demonstrated that using ply-based constitutive relations, trace-normalized stiffness properties can be derived for different materials. Theoretical predictions for trace-normalized parameters were plotted as functions of the unidirectional ply longitudinal modulus ( Ex), which defines the particular material system. Ply stiffness extensive empirical data were obtained from literature for four types of material systems (high modulus carbon/epoxy, standard modulus carbon/epoxy, aramid/epoxy, and glass/epoxy) and correlated quite well to theoretical predictions. Theoretical curves presented a nonlinear region for low Ex which gradually evolves to a plateau as Ex increases. It was verified that the master ply concept averaging the trace-normalized ply stiffness matrix elements can be applied for high modulus carbon/epoxy, standard modulus carbon/epoxy, and aramid/epoxy material systems. However, glass/epoxy systems can not be represented by this concept. The exposed theoretical background supports trace-based approach and enhances its effectiveness as a design tool, encompassing all the consequent advantages.


2004 ◽  
Vol 38 (8) ◽  
pp. 681-697 ◽  
Author(s):  
Steven J. DeTeresa ◽  
Dennis C. Freeman ◽  
Scott E. Groves

2007 ◽  
Vol 334-335 ◽  
pp. 365-368 ◽  
Author(s):  
Myung Gon Kim ◽  
Joong Sik Hong ◽  
Sang Guk Kang ◽  
Chun Gon Kim ◽  
Cheol Won Kong

The improvement of crack resistance is essential to the application of composites for cryogenic use such as structures storing liquid oxygen or liquid hydrogen. In this study, an effort to improve the crack resistance of a carbon/epoxy composite was made by adding MWNTs (Multi-Walled Carbon Nanotubes) to the resin formulation. Ahead of the investigation of MWNT effect, an epoxy matrix system was developed by mixing two kinds of epoxy resins and adding additives for high toughness at cryogenic temperature. The MWNT-added carbon/epoxy unidirectional prepregs were fabricated by way of a filament winding method with different concentrations of MWNTs (0.2wt% and 0.7wt%). The mechanical tests were performed inside an environmental chamber at room temperature and -150°C. The developed material system has little influence on interlaminar shear strength but resulted in higher fracture toughness at -150°C than those of baseline material. Microcrack densities after thermo-mechanical cycles were measured through an optical microscope.


Author(s):  
F. Shaapur

Non-uniform ion-thinning of heterogenous material structures has constituted a fundamental difficulty in preparation of specimens for transmission electron microscopy (TEM). A variety of corrective procedures have been developed and reported for reducing or eliminating the effect. Some of these techniques are applicable to any non-homogeneous material system and others only to unidirectionalfy heterogeneous samples. Recently, a procedure of the latter type has been developed which is mainly based on a new motion profile for the specimen rotation during ion-milling. This motion profile consists of reversing partial revolutions (RPR) within a fixed sector which is centered around a direction perpendicular to the specimen heterogeneity axis. The ion-milling results obtained through this technique, as studied on a number of thin film cross-sectional TEM (XTEM) specimens, have proved to be superior to those produced via other procedures.XTEM specimens from integrated circuit (IC) devices essentially form a complex unidirectional nonhomogeneous structure. The presence of a variety of mostly lateral features at different levels along the substrate surface (consisting of conductors, semiconductors, and insulators) generally cause non-uniform results if ion-thinned conventionally.


Author(s):  
F. Shaapur ◽  
M.J. Kim ◽  
Seh Kwang Lee ◽  
Soon Gwang Kim

TEM characterization and microanalysis of the recording media is crucial and complementary to new material system development as well as quality control applications. Due to the type of material generally used for supporting the medium, i.e., a polymer, conventional macro- and microthinning procedures for thin foil preparation are not applicable. Ultramicrotorny (UM) is a viable option and has been employed in previous similar studies. In this work UM has been used for preparation of XTEM samples from a magneto-optical (MO) recording medium in its original production format.The as-received material system consisted of a 4-layer, 2100 Å thick medium including a 300 Å TbFeCo layer enveloped by silicon nitride protective layers supported on a 1.2 mm thick × 135 mm (5.25 in.) diameter polycarbonate disk. Recording tracks had an approximate pitch of 1.6 μm separated by 800 Å deep peripheral grooves. Using a Buehler Isomet low-speed diamond saw, 1 mm wide and 20 mm long strips were cut out of the disk along the recording tracks.


Author(s):  
R. Rajesh ◽  
M.J. Kim ◽  
J.S. Bow ◽  
R.W. Carpenter ◽  
G.N. Maracas

In our previous work on MBE grown low temperature (LT) InP, attempts had been made to understand the relationships between the structural and electrical properties of this material system. Electrical measurements had established an enhancement of the resistivity of the phosphorus-rich LT InP layers with annealing under a P2 flux, which was directly correlated with the presence of second-phase particles. Further investigations, however, have revealed the presence of two fundamentally different types of precipitates. The first type are the surface particles, essentially an artefact of argon ion milling and containing mostly pure indium. The second type and the one more important to the study are the dense precipitates in the bulk of the annealed layers. These are phosphorus-rich and are believed to contribute to the improvement in the resistivity of the material.The observation of metallic indium islands solely in the annealed LT layers warranted further study in order to better understand the exact reasons for their formation.


Author(s):  
M. Kusiy

Introduction.  During the training of emergency specialists, the development of a clear, structured thinking is important.  And the mathematical disciplines themselves are aimed at activating the intellectual activity of cadets and students, the ability to think logically, consistently, and reasonably.  However, cadets and students consider mathematics to be a complex, inaccessible and not very necessary science.  Therefore, there is a need for continuous, continuous development of methods, technologies of forms of training that would increase interest, accessibility to mathematical disciplines and at the same time, were aimed at improving the quality of training of future rescuers. Purpose.  Identify the main stages of teaching higher mathematics for future civil defense specialists and substantiate their peculiarities. Methods.  The article used methods of scientific knowledge (general), methods used in the empirical and theoretical levels of research (transition from abstract to specific).  Results.  The basic stages of teaching higher mathematics for future specialists of civil defense are determined: motivation, research, assimilation, application.  The proposed stages are analyzed in detail.  The regularities that contribute to the increase of motivation (selection of educational material, system approach, creative approach, a variety of forms and methods of teaching, taking into account the specifics of the future profession, the use of innovative teaching technologies) are highlighted.  There are three phases of knowledge (curiosity, curiosity, theoretical knowledge).  It is determined that for the acquisition of knowledge it is possible to use the information - search type of classes with its microstructure.  Planning the microstructure of occupations in the first place should put the level of cognitive activity, awareness and independence in the performance of educational tasks.  It is noted that the process of assimilation is the process of internalization of knowledge, putting it into the inner plan of man, and the application is to extraorise knowledge, make it to the outline of human activity.  It was investigated that the stage of application of knowledge is divided into two parts (the first is the application of knowledge, skills in standard terms, the second - the transfer of knowledge, skills, skills in new, changed conditions).  Examples of applied tasks that can be solved in higher mathematics classes are given.  It is substantiated that only in combination of all stages is formed the need for knowledge acquisition and their application. Conclusion.  Stages of teaching higher mathematics - a cyclical process that requires constant improvement, hard work of the teacher.  Stages of motivation and application combine the same laws (selection of educational material, creative approach, taking into account the specifics of the future profession, the use of innovative teaching technologies).  And only in a logical, thought-out combination of these stages can one form the future need for civil protection specialists to expand the knowledge and apply it to practical application.


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