In his recent comment, Isabey discussed the issue of external stress/strain induced cellular stiffening. While the mechanism of this behavior is not fully understood and deserves further investigation, I would like to mention the cellular stiffening (increase of shear stiffness) that depends on the level of the endogenous contractile prestress (pre-tension) generated by myosin II-actin interactions.
Here you find a preprint version of a paper published in PRL 95, 114301 (2005) [also see Eur. Phys. J. E. 17, 261-281 (2005)] where the authors present a theory to explain why instabilities, e.g. stick-slip motion, is observed when cracks propagate in rubber materials.
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Are not as high as we expected although very stiff and strong nanotubes or nanofibers (Young’s modulus E~1000GPa) are added into soft polymer matrices like epoxy (E~4GPa). In our early investigation on the systematic mechanical property characterizations of nanocomposites (Xu et al., Journal of Composite Materials, 2004--among top 5 in 2005;and top 10 in 2006 of the Most-Frequently-Read Articles in Journal of Composite Materials.) have shown that there was a very small increase (sometimes even decrease) of critical ultimate tensile/bending strengths, and mode-I fracture toughnesses in spite of complete chemical treatments of the interfacial bonding area, and uniform dispersions of nanofibers (click to view a TEM image). Similar experimental results were often reported in recent years. Therefore, mechanics analysis is extremely valuable before we make these “expensive” nanocomposite materials. Our goal is to provide in-depth mechanics insight, and future directions for nanocomposite development. Till now, nanocomposite materials are promising as multi-functional materials, rather than structural materials. Here we mainly focus on two critical parameters for structural materials: tensile strength and fracture toughness. We notice that other mechanical parameters such as compressive strengths and Young’s moduli of nanocomposite materials have slight increase over their matrices.
Hello mechanicians,
What are the current research areas in computational mechanics? What is the future of CM? Where can one find such information on the net? Is there a central location?
In December 2007 Elsevier will organise the 2nd International Conference on Mechanics of Biomaterials & Tissues (www.icmobt.elsevier.com). The aim of the conference is to provide a forum for the discussion of the modeling and measurement of deformation and fracture behavior in biological materials and in those materials which are used to replace them in the human body.
The response of low-dimensional solid objects combines geometry and physics in unusual ways, exemplified in structures of great utility such as a thin-walled tube that is ubiquitous in nature and technology.
I was a little bit surprised in the introduction of this new forum to see mention of elastic and plastic contacts but no specific mention of viscoelastic contacts.
In the era of commercially-available instruments for indentation testing, the examination of viscoelastic contact mechanics, both in the context of polymers and biological tissues, seems to have taken on new life. To a first approximation, for indentation testing in the time domain, the fundamental mechanics has not much advanced beyond a few classic papers of the 1960s: Lee and Radok, J. Appl. Mech. 27 (1960) 438 and Ting TCT, J. Appl. Mech. 88 (1966) 845. However, the implementation of techniques for analysis of experimental data has progressed substantially. With spherical indenters the use of linearly viscoelastic models for characterization of a material creep or relaxation function is straightforward. Recent experimental studies have confirmed this, while more lingering questions remain for sharp contacts including Berkovich pyramidal indenters (most commonly shipped with commercial indenters). Sharp contacts seem to give rise to nonlinearly viscoelastic responses. Other topics of recent interest include frequency-domain measurements and examination of oscillating contacts and adhesion. (Although not mentioned in the listing of KLJ's most-loved topics in contact mechanics, viscoelastic contact has been the subject of several recent KLJ publications!) Although research in viscoelastic contact mechanics has been strong in recent years, perhaps a challenge remains in the dissemination of information and the establishment of approachable experimental techniques for use by non-experts.
When I was a graduate student, I spent several months to measure interfacial toughness between metalic (Cu and Au) films and thick substrates(Si and Polycarbonate). My methods were bulge test (blistering test) and 4-point bending test. I had many problems such as making an initial crack(pre-cracking), changing load phase angle applied to specimens, preparing/patterning thin films, constructing my own test apparatus, etc. The biggest problem was to measure the interfacial toughness over a wide range of loading phase angle. For a bimaterial with a non-zero oscillatory index(epsilon), we don't know the phase angle for a minimum interfacial toughness beforehand. Therefore, we need to measure the interfacial toughness over a wide range of phage angle. For engineering purpose, we need a minimum interfacial toughness value for reliability design because this value will lead to a conservative design of systems.
