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At least 145 records · Page 8
All sourcesNASA NTRSDOE OSTI
DOE OSTI2019

Material Property Determinations for Alluvium in Support of Source Physics Experiment

Two blocks of alluvium were extensively tested at the Sandia National Laboratories Geomechanics laboratory. The alluvium blocks are intended to serve as surrogate material for mechanical property determinations to support the SPE DAG experimental series. From constant mean stress triaxial testing, strength failure envelopes were parameterized and are presented for each block. Modulus and stress relationships are given including bulk modulus versus mean stress, shear modulus versus shear stress, Young's modulus versus axial stress and Poisson's ratio versus axial stress. In addition, P-&S-wave velocities, and porosity, determined using helium porosimetry, were obtained on each block. Generally, both Young's modulus and Poisson's ratio increase with increasing axial stress, bulk modulus increases with increasing pressure, and increases more dramatically upon pore crush, shear modulus decreases with increasing shear stress and then appears to plateau. The Unconfined Compressive Strength for the BM is in the range of 0.5-0.6, and for SM in the range of 2.0-2.6 MPa. The confined compressive strength increases with increasing confining pressure, and the BM alluvium is significantly weaker compared to SM alluvium for mean stress levels above 8 MPa.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Novel scanning electron microscope bulge test technique integrated with loading function

Membranes and film-on-substrate structures are critical elements for some devices in electronics industry and for Micro Electro Mechanical Systems devices. These structures are normally at the scale of micrometer or even nanometer. Thus, the measurement for the mechanical property of these membranes poses a challenge over the conventional measurements at macro-scales. In this study, a novel bulge test method is presented for the evaluation of mechanical property of micro thin membranes. Three aspects are discussed in the study: (a) A novel bulge test with a Scanning Electron Microscope system realizing the function of loading and measuring simultaneously; (b) a simplified Digital Image Correlation method for a height measurement; and (c) an imaging distortion correction by the introduction of a scanning Moiré method. Combined with the above techniques, biaxial modulus as well as Young's modulus of the polyimide film can be determined. Besides, a standard tensile test is conducted as an auxiliary experiment to validate the feasibility of the proposed method.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2016

FP-LAPW study of structural, electronic, elastic, mechanical and thermal properties of AlFe intermetallic

The structural, electronic, elastic, mechanical and thermal properties of AlFe intermetallic compound in B{sub 2}-type (CsCl) structure have been investigated using first-principles calculations. The exchange-correlation term was treated within generalized gradient approximation. Ground state properties i.e. lattice constants (a{sub 0}), bulk modulus (B) and first-order pressure derivative of bulk modulus (B’) are presented. The density of states are derived which show the metallic character of present compound. Our results for C{sub 11}, C{sub 12} and C{sub 44} agree well with previous theoretical data. Using Pugh’s criteria (B/G{sub H} < 1.75), brittle character of AlFe is satisfied. In addition shear modulus (G{sub H}), Young’s modulus (E), sound wave velocities and Debye temperature (θ{sub D}) have also been estimated.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

Inorganic polymers from laterite using activation with phosphoric acid and alkaline sodium silicate solution: Mechanical and microstructural properties

Geopolymers from laterite, an iron-rich soil available in developing countries, have great potential as building materials. In this work, laterite from Togo (Africa) was used to prepare geopolymers using both phosphoric acid and alkaline sodium silicate solution. Microstructural properties were investigated by scanning electron microscopy, X-ray powder diffraction and mercury porosimetry, whereas thermal properties were evaluated by thermal analyses. The local environment of iron was studied by X-ray Absorption Spectroscopy (XANES region). The mechanical properties were determined. Modulus of Rupture and Young's modulus fell in the ranges 3.3–4.5 MPa and 12–33 GPa, respectively, rendering the materials good candidates for construction purposes. Heating above 900 °C results in weight-gain, presumably due to iron redox reactions. X-ray Absorption Spectroscopy data evidence changes in the chemical and structural environments of iron following thermal treatment of geopolymers. These changes indicate interaction between the geopolymer structure and iron during heating, possibly leading to redox properties. -- Highlights: •Geopolymerization of laterite is promising for fabrication of building materials. •Both phosphoric acid and alkaline sodium silicate solution can be used for activation. •Thermally activated redox properties of the inorganic polymers were observed.

36 MATERIALS SCIENCE↗
DOE OSTI2021

VERA-Grizzly Ex-Core Calculations: Watts Bar Unit 1 Cycles 1-2

The critical structures that comprise light-water reactor (LWR) nuclear power plants are subjected to operating environments that can challenge their integrity. Structures in close proximity to the reactor core, such as the reactor pressure vessel (RPV) and the biological shield wall, are subjected to high levels of radiation emanating from the core, as well as elevated temperatures. As the US fleet of operating LWRs ages, the effects of these operating environments on the integrity of these structures must be considered to ensure their continued safe operation. Extending the lifetime of commercial reactors and maintaining the aging reactor fleet require accurate prediction of the exposure of ex-core components to neutron and photon radiation. In particular, concrete degradation studies must be performed to evaluate the safety and long-term operation of reactors with lifetime extensions. The concrete reactor bioshield is important for providing radiological protection during operation and must last for the entire lifetime of the reactor. Recent interest in lifetime extensions furthers the need to accurately simulate concrete material degradation in the reactor bioshield. As a result of this need, the Nuclear Energy Advanced Modeling and Simulation (NEAMS) program has funded this study to couple its tools, Virtual Environment for Reactor Applications (VERA) and Grizzly. VERA allows users to set up models to calculate time-dependent and fully coupled solutions (with thermal feedback) for ex-core quantities of interest such as vessel and coupon fluence and detector responses for multiple statepoints and cycles. Grizzly is a finite-element application based on the Multiphysics Object Oriented Simulation Environment (MOOSE) framework that is used to enable aging materials calculations. This report highlights the work performed to calculate the fluence in the vessel and concrete for Watts Bar Nuclear Plant Unit 1 (WBN1) Cycles 1 and 2. The fluences obtained from VERA were successfully transferred to Grizzly using a Python script. Four simulations were run with Grizzly: (1) the Mazars model with the initial Young’s modulus being the instantaneous modulus, (2) the Mazars model with the initial Young’s modulus being the delayed modulus, (3) the Mazars model with the initial Young’s modulus being the delayed modulus with the addition of the effects of micro-damage caused by irradiation, and (4) the Mazars model with the initial Young’s modulus being the instantaneous modulus, and with the addition of micro-damage and creep. Details regarding the methods used to obtain the fluence and the statistical errors associated with the VERA Monte Carlo Shift calculations are discussed in greater detail in this report. The results obtained from the four Grizzly models are also presented in this report.

21 SPECIFIC NUCLEAR REACTORS AND ASSOCIATED PLANTS↗
DOE OSTI2016

Microstructure and nanoindentation of the rostrum of Curculio longinasus Chittenden, 1927 (Coleoptera: Curculionidae)

The rostrum is an extension of the cuticle of the head of weevils (Coleoptera: Curculionidae) and is often used to bore holes for oviposition (the process of laying eggs) into host plant tissue where larval development occurs. In members of the genus Curculio Linnaeus, 1758, the rostrum is long, slender, and strongly curved, but is nevertheless used to excavate straight bore-holes in the fruit of various host plants, through significant deformation of this structure. In this study, scanning electron microscopy (SEM) was used to examine the rostrum of Curculio longinasus Chittenden, 1927, leading to a microstructural model that describes its deformation behavior. Specifically, we used the continuous stiffness measurement (CSM) technique in nanoindentation to measure the Young's modulus and hardness of rostrum. The values of Young's modulus and hardness for the endocuticle were measured to be 8.91 ± 0.93 GPa and 558 ± 60 MPa, respectively. These results are critical for generating accurate finite element models of the head's mechanical behavior while it undergoes deformation. - Highlights: •SEM was used to examine the rostrum of Curculio longinasus Chittenden, 1927. •Nanoindentation to measure the Young's modulus and hardness of rostrum. •Results are critical for finite element models of the head's mechanical behavior.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Elastic knowledge base of bcc Ti alloys from first-principles calculations and CALPHAD-based modeling

Here, titanium alloys are being investigated as suitable materials for load-bearing implants because of their biocompatibility and mechanical properties. Stress shielding, a common issue with the current load-bearing implant materials, occurs due to a Young’s modulus (E) mismatch between bone (~10–40 GPa) and implants (such as Ti-6Al-4V ~ 110 GPa), which leads to bone dying around the implant and ultimately implant failure. Reducing the Young’s modulus of Ti alloys may overcome the issues of stress shielding and improve implant materials. In the present work, first-principles calculations have been used to predict the single crystal elastic stiffness coefficients (c ij ’s) for the Ti-containing ternary alloys Ti-X-Y(X ≠ Y = Mo, Nb, Sn, Ta, Zr) in the bcc lattice. It is found that the ternary Ti-X-Y (X ≠ Y = Mo, Nb, Ta) alloys behave similarly; so do the ternary Ti-X-Sn (X = Mo, Nb, Ta) alloys and the Ti-X-Zr (X = Mo, Nb, Ta) alloys. This is expected due to the similarity between the Mo, Nb and Ta elements. The results also show that the Ti-Zr-X alloys stabilized the bcc phase at lower alloying concentrations. The polycrystalline aggregate properties are also estimated from the c ij ’s, including bulk modulus, shear modulus and Young’s modulus. The results show that Ti-alloys with compositions close to the bcc stability limit have the lowest E. In combination with previous predictions, a complete elastic database has been established using theCALPHAD (CALculation of PHAse Diagram) based modeling approach. The database results are compared with the E of higher order Ti alloys and shown to be able to predict the E accurately. This complete data-base forms a foundation to tailor Ti alloys for desired elastic properties.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Theoretical Investigation of the Mechanical and Thermodynamic Properties of the Layered Yttrium Diborocarbides

The mechanical, electronic, and thermodynamic properties of typical layered structure yttrium diborocarbides (YB{sub 2}C{sub 2}) were investigated by the density functional theory. The calculated lattice constants were slightly higher than the available experimental data. The elastic constants revealed that YB{sub 2}C{sub 2} was mechanically stable. The bulk modulus (190.8 GPa), shear modulus (127.4 GPa), Young’s modulus (312.7 GPa), Poisson’s ratio (0.227), and Vickers hardness (18–19 GPa) were obtained, and the ductility, plasticity, and elastic anisotropy were further analyzed. The total and partial density of states were also calculated, indicating that the metallic character was mainly attributed to the contribution from Y-4d states and weakly hybridized with the 2p states from the B and C atoms. Finally, we obtained the Debye, melting, and the superconducting transition temperatures of YB{sub 2}C{sub 2} as 824, 2239 and 2.38 K, respectively. Our study showed that YB{sub 2}C{sub 2} offers potential in superconductivity or ultrahigh temperature applications.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Thermoreversible and Injectable ABC Polypeptoid Hydrogels: Controlling the Hydrogel Properties through Molecular Design

Here, a series of ABC triblock copolypeptoids [i.e., poly( N -allyl glycine)- b -poly( N -methyl glycine)-b-poly( N -decyl glycine) (AMD)] with well-defined structure and varying composition have been synthesized by sequential primary amine-initiated ring-opening polymerization of the corresponding N-substituted N -carboxyanhydride monomers (Al-NCA, Me-NCA, and De-NCA). The ABC block copolypeptoids undergo sol-to-gel transitions with increasing temperature in water and biological media at low concentrations (2.5–10 wt %). The sol–gel transition is rapid and fully reversible with a narrow transition window, evidenced by the rheological measurements. The gelation temperature ( T gel ) and mechanical stiffness of the hydrogels are highly tunable: T gel in the 26.2–60.0 °C range, the storage modulus (G') and Young’s modulus ( E ) in the 0.2–780 Pa and 0.5–2346 Pa range, respectively, at the physiological temperature (37 °C) can be readily accessed by controlling the block copolypeptoid composition and the polymer solution concentration. The hydrogel is injectable through a 24 gauge syringe needle and maintains their shape upon in contact with surfaces or water baths that are kept above the sol–gel transition temperature. The hydrogels exhibit minimal cytotoxicity toward human adipose derived stem cells (hASCs), evidenced from both alamarBlue and PicoGreen assays. Furthermore, quantitative PCR analysis revealed significant up-regulation of the Col2a1 gene and down-regulation of ANGPT1 gene, suggesting that the hydrogel exhibit biological activity in inducing chondrogenesis of hASCs. It was also demonstrated that the hydrogel can be used to quantitatively encapsulate water-soluble enzymes (e.g., horseradish peroxidase) by manipulating the sol–gel transition. The enzymatic activity of HRP remain unperturbed after encapsulation at 37 °C for up to 7 d, suggesting that the hydrogel does not adversely affect the enzyme structure and thereby the enzymatic activity. These results suggest that the polypeptoid hydrogel a promising synthetic platform for tissue engineering or protein storage applications.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Electronic Structure and Mechanical Properties of Solvated Montmorillonite Clay Using Large-Scale DFT Method

Montmorillonite clay (MMT) has been widely used in engineering and environmental applications as a landfill barrier and toxic waste repository due to its unique property as an expandable clay mineral that can absorb water easily. This absorption process rendered MMT to be highly exothermic due to electrostatic interactions among molecules and hydrogen bonds between surface atoms. A detailed study of a large supercell model of structural clay enables us to predict long-term nuclear waste storage. Herein, a large solvent MMT model with 4071 atoms is studied using ab initio density functional theory. The DFT calculation and analysis clarify the important issues, such as bond strength, solvation effect, elasticity, and seismic wave velocities. These results are compared to our previous study on crystalline MMT (dry). The solvated MMT has reduced shear modulus (G), bulk modulus (K), and Young’s modulus (E). We observe that the conduction band (CB) in the density of states (DOS) of solvated MMT model has a single, conspicuous peak at –8.5 eV. Moreover, the atom-resolved partial density of states (PDOS) summarizes the roles played by each atom in the DOS. These findings illuminate numerous potential sophisticated applications of MMT clay.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Elastic properties of gold supracrystals: Effects of nanocrystal size, ligand length, and nanocrystallinity

Atomistic molecular dynamics simulations are performed to study the elastic properties of alkylthiol-functionalized gold supracrystals. The predicted Young’s and shear moduli are around 1 GPa and 100 MPa, respectively. We show that, with increasing NC size, the Young’s modulus decreases while the shear modulus essentially remains invariant; with increasing ligand length, the Young’s modulus increases but the shear modulus decreases. Moreover, significant increase in the Young’s modulus is seen when the polycrystalline NCs are replaced by single-crystal ones of the same size. All these are in reasonable agreement with available experiments. We attribute the mechanisms to the interaction between capping ligands as well as its variations caused by the change in ligand length and NC geometry. The results may deepen our understanding of elastic properties of the supracrystals and their influential factors.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2014

First-principles calculations of the electronic, vibrational, and elastic properties of the magnetic laminate Mn₂GaC

In this paper, we report the by first-principles predicted properties of the recently discovered magnetic MAX phase Mn₂GaC. The electronic band structure and vibrational dispersion relation, as well as the electronic and vibrational density of states, have been calculated. The band structure close to the Fermi level indicates anisotropy with respect to electrical conductivity, while the distribution of the electronic and vibrational states for both Mn and Ga depend on the chosen relative orientation of the Mn spins across the Ga sheets in the Mn–Ga–Mn trilayers. In addition, the elastic properties have been calculated, and from the five elastic constants, the Voigt bulk modulus is determined to be 157 GPa, the Voigt shear modulus 93 GPa, and the Young's modulus 233 GPa. Furthermore, Mn₂GaC is found relatively elastically isotropic, with a compression anisotropy factor of 0.97, and shear anisotropy factors of 0.9 and 1, respectively. The Poisson's ratio is 0.25. Evaluated elastic properties are compared to theoretical and experimental results for M₂AC phases where M = Ti, V, Cr, Zr, Nb, Ta, and A = Al, S, Ge, In, Sn.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2017

Characterization of Shear Properties for APO/MBI Syntactic Foam

Triaxial compression testing is a means for mechanical characterization of a material. A unique feature of the triaxial compression test is the application of two different magnitudes of compressive pressures on the material simultaneously. The material behavior under these different compressive pressures can be monitored over time. Several important characteristics of the material, such as stress yield values and the shear failure envelope may then be determined. Also mechanical properties such as Poisson’s ratio, Young’s modulus and bulk modulus can be determined from the triaxial compression test. The triaxial compression test was employed in this investigation to characterize the shear behavior, shear failure envelope, and mechanical properties of a syntactic foam. Los Alamos National Laboratory (LANL) supplied a total of 36 samples of APO-BMI syntactic foam to the University of New Mexico, Department of Civil Engineering for testing between December 2003 and May 2004. Each sample had a diameter of 1.395±0.005 in. (3.543±0.013cm.) and a length of 2.796±0.004 in. (7.102±0.010 cm.). The samples had an average density of 0.295 g/cm3. Additional information about the material tested in this investigation can be found in the “Specimen Description” section contained in Chapter 1. The nomenclatures used in this study is presented in Chapter 1. In addition to designing and implementing triaxial compression tests capable of up to 2,000 psi. confining pressure (minor principal stress) and roughly 13,000 psi. in axial pressure (major principal stress), a pure tension test was designed and conducted on the foam material. The purpose of this pure tension test was to obtain maximum tensile stress values to enhance the characterization of the shear envelope in the stress space. The sampling procedure and specimen preparation for a standard test can be found in the American Society for Testing Materials (ASTM) D 5379/ D 5379 – 93. The above tests mentioned and their procedures are discussed in Chapter 2. Chapter 2 contains the types of tests performed and the apparatus used for testing the material. Chapter 2 also has a brief explanation of the equipment and the procedures used for conducting the tests. In Chapter 3, the material characteristics and mechanical properties obtained from the tests are described; composite plots of deviatoric vs. mean stress and deviatoric stress vs. longitudinal strain are also included. The plots of deviatoric stress vs. mean stress clearly identify the shear envelope for the material. Chapter 4 summarizes the vital information obtained from the tests and the conclusions made. All the necessary plots and the data generated during the testing have been included in the Appendix. The information in the appendix includes plots of: Strain vs. Time, Stress vs. Time, Stress vs. Strain, Mean Stress vs. Volumetric Strain, Lateral Strain vs. Longitudinal Strain, and q vs. p. Bulk modulus, Poisson’s ratio, and Young’s modulus are displayed in the appropriate plots in each appendix.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Morphomechanical and structural changes induced by ROCK inhibitor in breast cancer cells

The EMT phenomenon is based on tumour progression. The cells lose their physiologic phenotype and assumed a mesenchymal phenotype characterized by an increased migratory capacity, invasiveness and high resistance to apoptosis. In this process, RHO family regulates the activation or suppression of ROCK (Rho-associated coiled-coil containing protein kinase) which in turn regulates the cytoskeleton dynamics. However, while the biochemical mechanisms are widely investigated, a comprehensive and careful estimation of biomechanical changes has not been extensively addressed. In this work, we used a strong ROCK inhibitor, Y-27632, to evaluate the effects of inhibition on living breast cancer epithelial cells by a biomechanical approach. Atomic Force Microscopy (AFM) was used to estimate changes of cellular elasticity, quantified by Young's modulus parameter. The morphometric alterations were analyzed by AFM topographies and Confocal Laser Scanning Microscopy (CLSM). Our study revealed a significant modification in the Young's modulus after treatment, especially as regards cytoskeletal region. Our evidences suggest that the use of Y-27632 enhanced the cell rigidity, preventing cell migration and arrested the metastasization process representing a potential powerful factor for cancer treatment. - Highlights: • RHO family regulated the activation or suppression of ROCK (Rho-associated protein kinase). • ROCK inhibitor (Y-2763) modified the Young Modulus's in the cytoskeletal region. • Y-2763 enhanced the cell rigidity and arrested metestatisation process. • Rock inhibitor reduction of cell elasticity envisaged novel antitumor therapies.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2020

Characterization of elastic mechanical properties of Tuscaloosa Marine Shale from well logs using the vertical transversely isotropic model

To avoid steep declines in the Tuscaloosa Marine Shale (TMS) production, wells are fracture-stimulated to release the hydrocarbons trapped in the matrix of the formation. An accurate estimation of Young’s modulus and Poisson’s ratio is essential for hydraulic fracture propagation. In addition, ignoring the highly heterogeneous and anisotropic character of TMS can lead to erroneous stress values, which subsequently affect hydraulic fracture width estimates and the overall hydraulic fracturing process. We have developed an empirical 1D geomechanical model that takes into account VTI anisotropy, and it is used to characterize the elastic mechanical properties of TMS in two wells. In the analyzed formation, the vertical Poisson’s ratio is less than the horizontal Poisson’s ratio, which suggests the necessity of an alternative to the ANNIE equations. The stiffness coefficients [Formula: see text] and [Formula: see text] were estimated using the relationships developed from the ultrasonic core data available for the two TMS. Further, correlations between the static and dynamic properties from laboratory tests were used to improve the minimum horizontal stress calculation. We compare VTI Young’s moduli, Poisson’s ratios, and minimum horizontal stress with the isotropic solution. VTI modeling improves the estimation of the elastic mechanical properties. The isotropic solution underestimates the minimum horizontal stress in the formation. Moreover, it was shown that the 20 ft shale interval below the TMS base is characterized by a low Young’s modulus (the vertical Young’s modulus is equal to 20 GPa, whereas the horizontal Young’s modulus is equal to 40 GPa) and may be a frac barrier.

Geochemistry & Geophysics↗
NASA NTRS2005

Multi-Scale Modeling of Cross-Linked Nanotube Materials

The effect of cross-linking single-walled carbon nanotubes on the Young's modulus of a nanotube-reinforced composite is modeled with a multi-scale method. The Young's modulus is predicted as a function of nanotube volume fraction and cross-link density. In this method, the constitutive properties of molecular representative volume elements are determined using molecular dynamics simulation and equivalent-continuum modeling. The Young's modulus is subsequently calculated for cross-linked nanotubes in a matrix which consists of the unreacted cross-linking agent. Two different cross-linking agents are used in this study, one that is short and rigid (Molecule A), and one that is long and flexible (Molecule B). Direct comparisons between the predicted elastic constants are made for the models in which the nanotubes are either covalently bonded or not chemically bonded to the cross-linking agent. At a nanotube volume fraction of 10%, the Young's modulus of Material A is not affected by nanotube crosslinking, while the Young's modulus of Material B is reduced by 64% when the nanotubes are cross-linked relative to the non-cross-linked material with the same matrix.

Frankland, S. J. V.↗
NASA NTRS1983

Fracture toughness/Young's modulus correlation for low-density fibrous silica bodies

Fracture toughness and static Young's modulus were measured for the low-density silic fiber materials used as tiles in the thermal protection system of the Space Shuttle. The fracture behavior was found to be in excellent agreement with a previously formulated micromechanical model and allowed both (density) classes of tile material to be correlated to a single function. A similar correlation was also found between strength and Young's modulus, which is the basis of a nondestructive evaluation test for these materials. It was shown that the value of Young's modulus determined from a dynamic test can be substantially greater than that determined in a static mechanical test. This effect must be taken into account in the correlation. Finally, it was also determined that these materials have significant variations in Kc, both within and between production units, so that the strength variability in these materials is dependent on both fracture toughness and flaw-size variations.

Green, D. J.↗
NASA NTRS1986

Shear characterization of unidirectional composites with the off-axis tension test

The influence of end constraints on accurate determination of the intralaminar shear modulus G(12) from an off-axis tension test is examined both analytically and experimentally. The Pagano-Halpin (1968) model is employed to illustrate that, when the effect of end constraints is properly considered, the exact expression for G(12) is obtained. When the effect of end constraints is neglected, expressions for the apparent shear modulus G(12)-asterisk and apparent Young's modulus Exx-asterisk are obtained. Numerical comparison for various off-axis configurations and aspect ratios is carried out using typical material properties for graphite/polyimide unidirectional composites. It is demonstrated that the end-constraint effect influences accurate determination of G(12) more adversely than it affects the laminate Young's modulus E(xx) in the low off-axis range. Experimental results obtained from off-axis tests on unidirectional graphite/polyimide specimens confirm the above. Based on the presented analytical and experimental evidence, the 45-deg off-axis coupon is proposed for the determination of the intralaminar shear modulus G(12).

Pindera, M.-J.↗