General principles and perspectives Specimen preparation Tension Compression Shear Flexure Through-thickness testing Interlaminar fracture toughness Impact and damage tolerance Fatigue Environmental testing of organic matrix composites Scaling effects in laminated composites Statistical modelling and testing of data variability Development and use of standard test methods.

Mechanical testing of advanced fibre composites

Compressive failure of composites, part I: Testing and micromechanical theories

Size effects in the testing of fibre-composite materials

Poly (ionic liquid)s attracted enormous attention as adsorbents for the CO2 separation from natural gas. Hence, in this work poly (1-butyl-3-vinylimidazolium bromide), P[VBIm][Br], poly (1-butyl-3-vinylimidazolium thiocyanate), P[VBIm][SCN], and poly (1-butyl-3-vinylimidazolium tetrafluoroborate), P[VBIm][BF4] were synthesized and evaluated their CO2 adsorption performance. The synthesized poly(ionic liquid)s were characterized by 1H NMR, FT-IR spectroscopy, and differential scanning calorimetery (DSC) analysis. The CO2 adsorption was studied at various temperatures and pressures by quartz crystal microbalance (QCM) and experimental data were correlated by a model of dual-mode. The Henry and Langmuir contributions in CO2 adsorption were evaluated. The obtained thermodynamics and kinetics parameters of CO2 adsorption reveal that CO2 adsorption has an exothermic and physisorption nature. Also, density functional theory (DFT) computations were done in order to assess interactions between poly(ionic liquid)s with CO2 gas. DFT computations corroborated that interaction of P[VBIm][SCN] with CO2 is stronger than those of other poly(ionic liquid)s.

经Co

Engineering Design: A Project-Based Introduction

Failure modes of unidirectional carbon/epoxy composite compression specimens

Various specimen sizes of an unreinforced polymer, Hercules 3501 -6 thermosetting epoxy, were subjected to a tensile test. The general specimen geometry was a rectangular dog-bone shape with constant gauge length, but with each specimen size having a different crosssectional area. These cross-sectional areas were obtained by varying the thickness of the epoxy during casting, and the gauge section width during grinding. The resulting failure surfaces of the specimens were observed and photographed using scanning electron microscopy. The results indicate that failure stress, dimensions of the critical flaw which caused failure, and a quantity which is proportional to the fracture toughness, are all correlated with specimen size.

Specimen size effect during tensile testing of an unreinforced polymer

A new Iosipescu shear test fixture design that can be used to perform the test procedure outlined in Test Method for Shear Properties of Composite Materials by the V-Notched Beam Method (ASTM D 5379) was designed, fabricated, and tested. The new fixture solves the often reported problems of specimen twisting, variability of results, and differences in measured shear modulus between [0]16, [0/90]4s, and [90]16 laminates. Lateral instability of the Iosipescu specimen is explored as the main agent causing the undesirable effects observed with the previous fixture design.

An Improved Iosipescu Shear Test Fixture

An experimental study was performed to determine the effect of type of tabbing material and tab taper on the measured axial compressive strength of a unidirectional carbon/epoxy material. Two types of tabbing materials (hot-rolled, low carbon steel and glass-fabric/epoxy) and two tab taper geometries (untapered and 30° taper) were utilized. Additionally, the influence of partial tab debonding on the measured compressive strength was determined. A standard IITRI compression test fixture was used. Tapered steel tabs provided consistently higher compressive strengths than tapered glass-fabric/epoxy tabs, or untapered steel or glass-fabric/epoxy tabs. Deliberately introducing regions of tab debonding in untapered glass-fabric/epoxy tabbed specimens resulted in only a small decrease in compressive strength.

Influence of Specimen Tabs on the Compressive Strength of a Unidirectional Composite Material

The interaction between the isopescu shear-test specimen and the modified Wyoming shear-test fixture was investigated. This involved three areas of study. First, strip strain gages were applied to the specimen contact surfaces to measure strains induced by the fixture. While it has generally been assumed that the fixture induces an asymmetric load into the specimen, the measured strains indicated a nonasymmetric loading. Second, the effect of an out-of-plane moment, externally applied to the fixture, on gage section shear strains was observed. The shear strains observed were small leading to the conclusion that the fixture is very resistant to out-of-plane moments. Finally, the effect of fixture misalignment on the observed shear modulus was determined. The results indicate that the observed shear modulus increased significantly for slight amounts of misalignment. Therefore, experimental techniques should be modified to include a check for misalignment. Beyond this, it is suggested that the fixture design be modified to prevent misalignment and to achieve an asymmetric loading of the specimen.

Edwin Odom

Papers

Failure modes of unidirectional carbon/epoxy composite compression specimens

Specimen size effect during tensile testing of an unreinforced polymer

An Improved Iosipescu Shear Test Fixture

Influence of Specimen Tabs on the Compressive Strength of a Unidirectional Composite Material

Experimental and analytical investigation of the modified wyoming shear-test fixture