Pinch and swell structures: evidence for brittle-viscous behaviour in the middle crust

Abstract. The flow properties of middle to lower crustal rocks are commonly represented by viscous flow. However, examples of pinch and swell structures found in a mid-crustal high strain zone at St. Anne Point (Fiordland, New Zealand) suggest pinch and swell structures are initiated by brittle failure of the more competent layer in conjunction with material softening. On this basis we develop a flexible numerical model using brittle-viscous flow where Mohr–Coulomb failure is utilised to initiate pinch and swell structure development. Results show that pinch and swell structures develop in a competent layer in both Newtonian and non-Newtonian flow provided the competent layer has enough viscosity contrast and initially fails brittlely. The degree of material softening after initial failure is shown to impact pinch and swell characteristics with high rates of material softening causing the formation of thick necks between swells by limiting the successful localisation of strain. The flow regime and yielding characteristics of the matrix do not impact pinch and swell structure formation itself, so long as the matrix is less competent. To aid analysis of the structures and help derive the flow properties of rocks in the field, we define three stages of pinch and swell development and offer suggestions for measurements to be made in the field. Our study suggests that Mohr–Coulomb behaviour combined with viscous flow is an appropriate way to represent the heterogeneous rocks of the middle to lower crust. This type of mid-crustal rheological behaviour has significant influence on the localization of strain at all scales. For example, inclusion of Mohr–Coulomb brittle failure with viscous flow in just some mid-crustal layers within a crustal scale model will result in strain localisation throughout the whole crustal section allowing the development of through-going high strain structures from the upper crust into the middle and lower crust. This localization then has a significant effect on developing near-surface structures.

Download Full-text

Pinch and swell structures: evidence for strain localisation by brittle–viscous behaviour in the middle crust

Solid Earth ◽

10.5194/se-6-1045-2015 ◽

2015 ◽

Vol 6 (3) ◽

pp. 1045-1061 ◽

Cited By ~ 14

Author(s):

R. L. Gardner ◽

S. Piazolo ◽

N. R. Daczko

Keyword(s):

Viscous Flow ◽

Country Rock ◽

Shear Bands ◽

Rheological Behaviour ◽

Scale Model ◽

Flow Properties ◽

Strain Localisation ◽

Near Surface ◽

Middle Crust ◽

Alternative Representation

Abstract. The flow properties of middle crustal rocks are commonly represented by viscous flow. Examples of pinch and swell structures found in a high strain zone at St. Anne Point (Fiordland, New Zealand) and Wongwibinda (N.S.W., Australia) suggest pinch and swell structures may be initiated by brittle failure of the more competent layer in conjunction with subsequent material softening. On this basis we develop a numerical model where Mohr–Coulomb constitutive strain localising behaviour is utilised to initiate pinch and swell structure development. Results show that pinch and swell structures develop in a competent layer in both Newtonian and non-Newtonian flow, provided the competent layer has sufficient viscosity contrast and can localise strain to form shear bands. The flow regime and strain localising characteristics of the surrounding country rock appear not to impact pinch and swell structure formation. The degree of material softening after the initial strain localising behaviour is shown to impact pinch and swell characteristics, while extensive material softening causes the formation of thick necks between swells by limiting the focused localisation of strain into shear bands. To aid analysis of the structures and help derive the flow properties of rocks in the field, we define three stages of pinch and swell development and offer suggestions for measurements to be made in the field. Our study suggests that Mohr–Coulomb strain localising behaviour combined with viscous flow is a viable alternative representation of the heterogeneous rheological behaviour of rocks seen in the middle crust. This type of mid-crustal rheological behaviour can have significant influence on the localisation of strain at all scales. For example, inclusion of Mohr–Coulomb strain localising behaviour with viscous flow in just some mid-crustal layers within a crustal-scale model can result in significant strain localisation, extending from the upper crust into the middle crust. This localisation also influences the development of near-surface structures.

Download Full-text

Rheological Behaviour of PP/PET and Modified PP/PET Blends. I. Steady State Flow Properties

Polymers and Polymer Composites ◽

10.1177/096739110301100607 ◽

2003 ◽

Vol 11 (6) ◽

pp. 487-503 ◽

Cited By ~ 1

Author(s):

Natalie Zdrazilova ◽

Berenika Hausnerova ◽

Takeshi Kitano ◽

Petr Saha

Keyword(s):

Maleic Anhydride ◽

Normal Stress ◽

Shear Viscosity ◽

Rheological Behaviour ◽

Normal Stress Difference ◽

Stress Difference ◽

Flow Properties ◽

Complex Situation ◽

First Normal Stress Difference ◽

The Matrix

Both polypropylene (PP) and polyethylene terephthalate (PET) constitute a significant portion of post-consumer waste. To improve the recycling of immiscible PP/PET blends, a compatibiliser should be utilised. The steady shear flow properties of unmodified and modified PP/PET blends having up to 50 wt.% PET were investigated and compared in this study. Three types of PPs with different flow properties were used to ascertain the influence of the matrix on the blend's rheology. The effect of modification on the rheological properties was evaluated in two ways - firstly, the addition of 1 wt.% of maleic anhydride (MA), and secondly, the use of already modified polypropylene. According to the morphological observations, an improvement in compatibility was found in both cases. The shear viscosity and the first normal stress difference were measured using a rotational cone and plate rheometer at 265°C (when both PET and PP are molten), and 245°C (when only PP has melted). Completely different behaviour was observed under these two temperature conditions. At 265°C, the shear viscosity decreases with PET content in the blend, while at 245°C it increases, thus recalling the behaviour of particle-filled systems. The addition of maleic anhydride affects the shear viscosity in various ways; a decrease, an increase, and some almost unchanged values were obtained. Concerning the first normal stress difference, an even more complex situation occurs, and the effect of modification by MA is also ambiguous. Furthermore, the deviations from the log-additivity rule were evaluated in terms of the shear viscosity and the first normal stress difference. From the results, it can be supposed that PP-X/PET samples were compatibilised successfully, and strong interphase interactions could be expected. Finally, the yield values of shear stress determined at 245°C showed a generally increasing tendency with increasing PET content.

Download Full-text

The rheological behaviour and thermal ageing characteristics of PP/MWCNT/glass fibre multiscale composites

Polymers and Polymer Composites ◽

10.1177/0967391121992909 ◽

2021 ◽

pp. 096739112199290

Author(s):

N Rasana ◽

K Jayanarayanan ◽

Krishna Prasad Rajan ◽

Aravinthan Gopanna

Keyword(s):

Hybrid Composites ◽

Rheological Behaviour ◽

Strain Energy Release ◽

Critical Stress Intensity Factor ◽

Thermal Ageing ◽

Multiwalled Carbon ◽

Weight Percentage ◽

Fixed Weight ◽

Multiscale Composite ◽

The Matrix

Multiscale hybrid composites were prepared using varying weight percentages (0 to 5) of multiwalled carbon nanotubes (MWCNTs) as nanofiller and a fixed weight percentage (20) of short glass fibres as micro filler (in polypropylene (PP) matrix. The shear and extensional viscosity of the composites was measured using a capillary rheometer. It was observed that even at higher shear rates the synergism of micro and nanofillers in the matrix significantly enhanced the melt viscosity. The complex nanotube network entanglement with micro fillers and PP chains imparted restrictions to the polymer chain movements. The prepared samples were subjected to thermal ageing at 100°C for 4 days in hot air oven. After ageing, multiscale composite with 3 wt% MWCNTs exhibited 28.57% enhancement in strain at break, whereas the tensile strength and modulus reduced by 6.8% and 8% respectively. The fracture toughness properties like strain energy release rate and critical stress intensity factor were not affected for multiscale composite at the optimum content of 3 wt% MWCNT, even after thermal ageing.

Download Full-text

Viscous-flow properties of acetone solutions of vinylidene fluoride ? tetrafluoroethylene copolymer

Fibre Chemistry ◽

10.1007/bf00551093 ◽

1983 ◽

Vol 14 (3) ◽

pp. 210-211

Author(s):

B. S. Vesaite ◽

A. Girlyavichyus ◽

A. I. Logvinov ◽

L. Ya. Madorskaya ◽

A. V. Bezprozvannykh ◽

...

Keyword(s):

Viscous Flow ◽

Vinylidene Fluoride ◽

Flow Properties

Download Full-text

Analysis of viscous flow properties of styrene–butadiene–styrene-modified asphalt

Construction and Building Materials ◽

10.1016/j.conbuildmat.2019.116881 ◽

2019 ◽

Vol 229 ◽

pp. 116881

Author(s):

Zhan Ding ◽

Jing Zhang ◽

Peilong Li ◽

Xiangjing Yue ◽

Hui Bing

Keyword(s):

Viscous Flow ◽

Flow Properties ◽

Modified Asphalt ◽

Styrene Butadiene Styrene ◽

Styrene Butadiene ◽

Butadiene Styrene

Download Full-text

Multi-Scale Analysis of a Refractory Composite

Recent Advances in Solids and Structures ◽

10.1115/imece2005-79218 ◽

2005 ◽

Author(s):

Y. W. Kwon ◽

T. Chu ◽

D. Kim

Keyword(s):

Coating Layer ◽

Matrix Material ◽

Design Tool ◽

Scale Model ◽

High Temperature Application ◽

Multi Scale ◽

Matrix Layer ◽

The Matrix ◽

Temperature Application ◽

Refractory Composite

A refractory composite for a high temperature application was studied at various length scales, and its effective thermo-mechanical properties were computed. The analysis considered a micro-scale model made of a representative carbon fiber, a matrix layer, and a coating layer. The model included weak tangential bonding of the intra-layer of the matrix material in order to reduce the thermal stress occurring in the coating material caused by mismatch of coefficients of thermal expansions. In addition, unit-cell models for a 3-D braided composite and a plane-weave composite were also studied. The modeling technique developed in this study can be used as a design tool for an optimal refractory composite for a given application.

Download Full-text

A Yield Criterion for Porous Ductile Media at High Strain Rate

Journal of Applied Mechanics ◽

10.1115/1.2788921 ◽

1997 ◽

Vol 64 (3) ◽

pp. 503-509 ◽

Cited By ~ 17

Author(s):

Ze-Ping Wang ◽

Qing Jiang

Keyword(s):

High Strain Rate ◽

Strain Rate ◽

Yield Surface ◽

High Strain ◽

Yield Criterion ◽

Matrix Material ◽

Yield Function ◽

Inertial Effects ◽

The Matrix ◽

Dynamic Yield

An approximate yield criterion for porous ductile media at high strain rate is developed adopting energy principles. A new concept that the macroscopic stresses are composed of two parts, representing dynamic and quasi-static components, is proposed. It is found that the dynamic part of the macroscopic stresses controls the movement of the dynamic yield surface in stress space, while the quasi-static part determines the shape of the dynamic yield surface. The matrix material is idealized as rigid-perfectly plastic and obeying the von Mises yield. An approximate velocity field for the matrix is employed to derive the dynamic yield function. Numerical results show that the dynamic yield function is dependent not only on the rate of deformation but also on the distribution of initial micro-damage, which are different from that of the quasi-static condition. It is indicated that inertial effects play a very important role in the dynamic behavior of the yield function. However, it is also shown that when the rate of deformation is low (≤103/sec), inertial effects become vanishingly small, and the dynamic yield function in this case reduces to the Gurson model.

Download Full-text

Effect of the Loading Rate on Failure of Composite Pressure Vessel

Volume 5: High-Pressure Technology; ASME NDE Division; Rudy Scavuzzo Student Paper Symposium ◽

10.1115/pvp2013-97159 ◽

2013 ◽

Author(s):

Heng-Yi Chou ◽

Anthony Bunsell ◽

Georg Mair ◽

Alain Thionnet

Keyword(s):

Damage Accumulation ◽

Loading Rate ◽

Matrix Material ◽

Pressure Vessels ◽

Scale Model ◽

Loading Rates ◽

Multi Scale ◽

Composite Pressure Vessel ◽

The Matrix ◽

Pressurisation Test

A multi-scale model has been successfully applied to the simulation of the effects of pressurisation rate on damage accumulation in carbon fibre/epoxy plates and composite pressure vessels. The results of the simulations agree with experimental results and reveal that the point at which the structures become unstable in a monotonic pressurisation test depends on the speed of loading. The faster the loading rate the higher the applied stress at which the composite structure becomes unstable. The mechanism which governs this behaviour is seen to be the viscoelastic nature of the matrix material through which stresses are transferred from broken to neighbouring intact fibres. At loading rates that allow greater relaxation of the resin around fibre breaks neighbouring fibres are subjected to increased loads over a significantly greater length, leading to further earlier breaks.

Download Full-text