Dynamic mode-I delamination of composite laminates using a drop-weight tower and optical data-acquisition

Impact events can hardly be called quasi-static. To test for relevant properties with quasi-static test methods thus seems to make little sense, especially when materials with a rate-sensitivity are the subject of testing. Therefore, a test setup is developed to obtain the trac-tion-separation behaviour and fracture toughness of composites in mode I delamination at impact rates of deformation. An optical technique is applied to obtain the load-deflection curve, allowing for contactless measurements

Influence of the gripping fixture on the modified compact tension test results: evaluation of the experiments on cylindrical concrete speciments

The modified compact tension test (MCT) might become in the future a stable test configuration for the evaluation of fracture-mechanics parameters or also for description of fatigue behavior of composites materials such as concrete. Core drilling is used for sampling of existing structures. These samples have cylindrical shape with the selected thickness to avoid the stress concentration. This contribution focuses on the evaluation of the fracture behavior during static and quasi static tests. Static tests are performed on standard specimen with diameter 150 mm and length 300 mm. The quasi-static tests are performed using two different gripping fixtures. The results for quasi-static tests are represented as L-COD diagrams (i.e. load vs. crack opening displacement) measured on the loading axis. The comparison of results and discussion of advantages and disadvantages are introduced

Influence of the gripping fixture on the modified compact tension test results: evaluation of the experiments on cylindrical concrete speciments

The modified compact tension test (MCT) might become in the future a stable test configuration for the evaluation of fracture-mechanics parameters or also for description of fatigue behavior of composites materials such as concrete. Core drilling is used for sampling of existing structures. These samples have cylindrical shape with the selected thickness to avoid the stress concentration. This contribution focuses on the evaluation of the fracture behavior during static and quasi static tests. Static tests are performed on standard specimen with diameter 150 mm and length 300 mm. The quasi-static tests are performed using two different gripping fixtures. The results for quasi-static tests are represented as L-COD diagrams (i.e. load vs. crack opening displacement) measured on the loading axis. The comparison of results and discussion of advantages and disadvantages are introduced

Restriced Cost Functions and the Rate of Return to Quasi-Fixed Factors, with an Application to R&D and Capital in the Bell System

This paper provides a statistical test to assess the adequacy of static equilibrium models. The test is based on a restricted cost function framework together with the envelope conditions which characterize static equilibrium for the quasi-fixed factors. We also show how restricted cost function models can be exploited to investigate some important issues such as the calculation of the rates of return to quasi-fixed factors, the determination of over- or underinvestment in particular assets, and the distinction between short run excess capacity and long run economies of scale. We provide an empirical application of these techniques to data on the Bell System for the period 1947-1976, treating the stocks of physical capital and of research and development (R&D) as quasi-fixed inputs. The results suggest that there was substantial overinvestment in capital and underinvestment in R&D compared to the static equilibrium levels, and that the rates of return to capital and R&D were about 4.5 and 10-15 percent, respectively.

Fatigue delamination behaviour of unidirectional carbon fibre/epoxy laminates reinforced by Z-Fiber® pinnin

-Pin reinforced carbon-fibre epoxy laminates were tested under Mode I and Mode II conditions, both quasi-statically and in fatigue. Test procedures were adapted from existing standard or pre-standard tests. Samples containing 2% and 4% areal densities of carbon-fibre Z-pins (0.28mm diameter) were compared with unpinned laminates. Quasi-static tests under displacement control yielded a dramatic increase of the apparent delamination resistance. Specimens with 2% pin density failed in Mode I at loads 170N, equivalent to an apparent GIC of 2kJ/m2. Fatigue testing under load control showed that the presence of the through- thickness reinforcement slowed down fatigue delamination propagation

Biocompatibility assessment of silk nanoparticles : hemocompatibility and internalization by human blood cells

Many nanoparticles are designed for use as potential nanomedicines for parenteral administration. However, emerging evidence suggests that hemocompatibility is important, but is highly particle- and test-bed dependent. Thus, knowledge of bulk material properties does not predict the hemocompatibility of uncharacterized nanoparticles, including silk nanoparticles. This study compares the hemocompatibility of silk versus silica nanoparticles, using whole human blood under quasi-static and flow conditions. Substantial hemocompatibility differences are noted for some nanoparticles in quasi-static versus dynamic studies; i.e., the inflammatory response to silk nanoparticles is significantly lower under flow versus quasi-static conditions. Silk nanoparticles also have very low coagulant properties - an observation that scales from the macro- to the nano-level. These nanoparticle hemocompatibility studies are complemented by preliminary live cell measurements to evaluate the endocytosis and trafficking of nanoparticles in human blood cells. Overall, this study demonstrates that nanoparticle hemocompatibility is affected by several factors, including the test bed design

Failure mechanics in low-velocity impacts on thin composite plates

Eight-ply quasi-isotropic composite plates of Thornel 300 graphite in Narmco 5208 epoxy resin (T300/5208) were tested to establish the degree of equivalence between low-velocity impact and static testing. Both the deformation and failure mechanics under impact were representable by static indentation tests. Under low-velocity impacts such as tool drops, the dominant deformation mode of the plates was the first, or static, mode. Higher modes are excited on contact, but they decay significantly by the time the first-mode load reaches a maximum. The delamination patterns were observed by X-ray analysis. The areas of maximum delamination patterns were observed by X-ray analysis. The areas of maximum delamination coincided with the areas of highest peel stresses. The extent of delamination was similar for static and impact tests. Fiber failure damage was established by tensile tests on small fiber bundles obtained by deplying test specimens. The onset of fiber damage was in internal plies near the lower surface of the plates. The distribution and amount of fiber damage was similar fo impact and static tests

Reversible Rail Shear Apparatus Applied to the Study of Woven Laminate Shear Behavior

The multitude of in-plane shear tests existing in the literature seems to demonstrate the complexity of developing a test adapted to all experimental works. In a general framework of investigation of translaminar cracks in thin laminates, a test able to reproduce a pure in-plane shear loading was required. The laminate studied is notably employed as helicopter blade skin, and cyclic torsion induced by aerodynamic load involves cyclic in-plane shear. This particular application established some specifications for the test needed to carry out this study. To comply with them, an original technological solution has been developed from a three-rail shear test apparatus. This paper describes the resulting “reversible rail shear test” solution and its application to the study of in-plane shear behavior of a thin glass-epoxy laminate. The results concern plain and notched coupons under quasi-static loading, and crack growth tests under cyclic loading