On the Degree of Irreversibility of Friction in Sheared Soft Adhesive Contacts

A number of authors have experimentally assessed the influence of friction on adhesive contacts, and generally the contact area has been found to decrease due to tangential shear stresses at the interface. The decrease is however generally much smaller than that predicted already by the Savkoor and Briggs 1977 classical theory using “brittle” fracture mechanics mixed mode model extending the JKR (Griffith like) solution to the contact problem. The Savkoor and Briggs theory has two strong assumptions, namely that (i) shear tractions are also singular at the interface, whereas they have been found to follow a rather constant distribution, and that (ii) no dissipation occurs in the contact. While assumption (ii) has been extensively discussed in the Literature the role of assumption (i) remained unclear. We show that assuming entirely reversible slip at the interface with a constant shear stress fracture mechanics model leads to results almost indistinguishable from the Savkoor and Briggs model (and further in disagreement with experiments), hence it is assumption (ii) that critically affects the results. We analyze a large set of experimental data from Literature and show that the degree of irreversibility of friction can vary by orders of magnitude, despite similar materials and geometries, depending on the velocity at which the tangential load is applied.

Study on Finite Element Model for Splitting Capacity of Bamboo Culms

For the problem of bamboo structure safety caused by bamboo culms splitting, the bamboo culms splitting capacity test method is studied, bamboo culms splitting capacity finite element model based on brittle fracture mechanics is proposed in the work. The results calculated by FEM are consistent with the experimental results, and the error is in 20% or less. The bamboo culms splitting capacity finite element model established above can provide supports for bamboo culms wide engineering applications. The developed model has theory and engineering significance for digital bamboo building optimal design.

Research on Finite Element Model for Parallel to Bamboo Culms Axial Shear

For the issues of bamboo structure safety caused by parallel to bamboo culms axial shear, shear capacity test method is studied, parallel to bamboo culms axial shear capacity finite element model based on brittle fracture mechanics is proposed in the work. The results calculated by FEM are consistent with the experimental results, and the error is in 16% or less. The parallel to bamboo culms axial shear capacity finite element model established above can provide supports for bamboo culms wide engineering applications. The developed model has theory and engineering significance for digital bamboo building optimal design.

Growth Pattern Study of Closed Surface Flaw under Compression

Under extra compressive stress, some phenomena of rock spallings and fractures often exist on rock mass located in sidewalls of underground house and tunnels. It is the reason that the crack growth and coalescence initiation from original flaws (or faults) in rock mass. In the previous studies, many researchers took a flaw as a through flaw (2-dimentional model), but the flaws are not always through the whole rock mass in fact, most of them are only near the surface of rock mass, These are so named as surface flaws. They belong to three dimensional (2-D) flaws. Now, the reports on initiation and growth of 3-D surface flaw are few. So, for the investigation on growth patterns of 3-D surface flaw, a series of samples containing a surface flaw were carried out using frozen casting resin material at about -30°C temperatures. The surface flaw was made of a polyester film was used to model a single closed flaw on rock mass. The experimental results show that the wrapping wing crack (Mode I) initiated at the ends (or tips) of surface flaw first, and then formed a kinking zone (mixed crack zone) at a certain place at the middle of surface flaw region. Some petal cracks (Mode III) and shell-shaped cracks (Mode III) would grow at the middle place of flaw. A big fin crack (Mixed Mode) also emerged in middle of flaw and grown along loading direction. Finally, a team of large cracking curved faces deformed inside the resin specimen; the whole specimen would be splitted off by the initiation and growth of the cracks. The reasons lead to the fracture patterns of 3-D closed surface flaw were provided with brittle fracture mechanics theory in the article, preliminarily.