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Journal Club October 2010: Mechanical behaviour of highly packed particulate composites

Henry Tan's picture

Materials such as sedimentary rocks, pharmaceutical tablets, plastic bonded explosives, biscuits, concretes, nacre, solid propellants, seashells and asphalts can be treated as particulate composites that consist of particles of high volume fraction, matrixes of thin layer and interfaces of high specific surface area. Mechanical behaviour of highly packed particulate composites is the theme of this issue of Journal Club forum.

highly packed particulate composites

1. Sedimentary rocks, covering almost the entire ocean floor and about three-quarters of the Earth's land area, are made of sediments cemented or compacted together by a particular force or process over time. Damaged sedimentary rocks, such as those during oil and gas extraction or subsea oil spilling, may cause manmade earthquake. On the other side, studies on the behaviour of sedimentary rocks can bring benefits to petroleum industry such as in improving the drilling efficiency. Behaviour of sedimentary rocks are important in many fields of earth sciences, partly because they relate to the sudden rock failure that contributes to earthquakes, and partly because they forms permeable paths for fluid flow in fault zones (Gudmundsson et al., in press)

2. For pulsatile drug delivery, an osmotic tablet consists of a medical core surrounded by a coating made of a material that is water-insoluble but permeable. The pressure build-up in the core pushes the coating for drug release (Rahemba et al., 2009). For a coating made of particulate composites, the percolation of interfaces can provide a controllable way for drug delivery.

3. Energetic materials such as plastic bonded explosives and solid rocket propellants consist of particles of high volume fraction embedded in a polymeric binder. During slow loading, crack propagation is mainly along interfaces, particles are not fractured rather the crack deviates over or under them. Burning occurs on the pressured surface, the network of debonded interfaces allows hot gas access to increased internal surface area and thereby increases the burning rates, which further accelerate the debonding. The network close to the surface triggers the burn--to-violent-reaction (BVR) transition (Gould et al., 2009).

4. In many structured food applications, mixed biopolymer gels are utilised that exhibit typical emulsion-like phase-separated microstructures, which include spherical particles of one phase (e.g. maltodextrin) within a continuous matrix of the second (e.g. gelatin). One of the greatest challenges in the food industries is to develop products that can fracture in a pre-designed way so that they can provide the required function (Brink et al., 2007).

5. A concrete is made of a cement matrix that bonds particles of different size (gravels and sands) and fills the interstitial space. Sudden debonding and networking of interfaces causes the brittle weakness; chemical and nuclear plants can be at risk from earthquake since the protecting concrete structures can be vulnerable.

6. Nacre, produced by some molluscs as an inner shell layer and known as the “mother of pearl”, consists of about 95% (weight) inorganic aragonite platelets and a few percent of organic biopolymer, forming a brick-and-mortar like network; when under attack the network reorganize to spread out the energy of the blow across the shell layer. Further, aragonite platelets are also particulate composite materials consists of nanograins and biopolymer binder, as discovered in an Atomic Force Microscope observation (Li and Huang, 2009). This two-scale (micro-nanoscale) ceramic/polymer composite material is of an extraordinary beauty, very strong and resilient.



Gudmundsson A, Simmenes TH, Larsen B, Philipp SL (in press) Effects of internal structure and local stresses on fracture propagation, deflection, and arrest in fault zones. J. Struct. Geol.

Rahemba TR, Bell S, Connolly EK, Waterman KC (2009) Use of scoring to induce reproducible drug delivery from osmotic pulsatile tablets. Pharm. Dev. Technol. 14:548–555.

Brink J, Langton M, Stading M, Hermansson AM (2007) Simultaneous analysis of the structural and mechanical changes during large deformation of whey protein isolate/gelatin gels at the macro and micro levels. Food Hydrocolloids 21:409–419.

Gould PJ, Porter D, Cullis IG (2009) Predicting the damage/failure transition in polymer-bonded explosives. Proceedings of the 9th International Conference on Mechanical and Physical Behaviour of Materials under High Rate Loading, DYMAT 2009, EDP Sciences, pp. 1629-1633.

Li X, Huang Z (2009) Unveiling the Formation Mechanism of Pseudo-Single-Crystal Aragonite Platelets in Nacre, Phys Rev Lett, 102, 075502.



Xiaodong Li's picture

Thanks a lot Henry. I agree. Mother nature has developed many unique recipes for making materials that exhibit superior mechanical (as well as other) properties to engineering materials. Nacre is a model example. Recently, people found that bamboo fibers are made of nanoparticles (densily packed), as shown below. This may help explain why bamboo is so strong and tough. Mother nature is an excellent teacher. Your suggestions on more examples of highly packed nanopartilce composites are highly appreciated. 

L. H. Zou, H. Jin, W. Y. Lu, and X. D. Li, "Nanoscale
Structural and Mechanical Characterization of the Cell Wall of Bamboo
Fibers," Materials Science and Engineering C, 28 (2009) 1501-1508. 

Henry Tan's picture

Thank you Xiaodong,

I am working on quantitatively characterizing the behaviour of plants including bamboo though X-ray tomography test and numerical simulation. Currently our advanced X-ray tomography can reach the scale of several tens of nanometres. Your work at the nanoscale using the Atomic Force Microscope is a great input to my work.

Plants are of great interest to me because of the potential to provide materials with low, or negative, carbon footprint which can be used in manufacturing and construction. Research of plants including bamboo at the nano and microscopic scale is important for designing the micro-structural features that control the properties of material.

Zhigang Suo's picture

Dear Henry:  Thank you so much for this intriguing post.  Rizhi Wang did some experiments to show that, on loading, nacre develops distributed damage, and gives rise to some ductivity.  Together we explored possible mechanisms for this behavior.  His beautiful micrographs and some of our ideas were reported in this paper:

R.Z. Wang, Z. Suo, A.G. Evans, I.A. Aksay, N. Yao, "Deformation mechanisms in nacre," J. Mater. Res., 16,2485-2493, 2001

I wonder if you have thought of ductile behavior in highly packed particulate composites.

Xiaodong Li's picture

Thanks a lot Zhigang. This JMR paper has been highly cited. I like this paper very much.  I have read this paper many times. Your findings about surface nanoasperities of nacre's aragonite platelets and their contributions to the inelasticity/ductility are very novel. This paper (from Rizhi, you, Tony, I.A Aksay and Nan) has stimulated lots of interest in studying nacre. Katti et al. showed through finite element modeling that the nanointerlocks (surface nanoasperities) between aragonite platelets play an important role in the strengthening and toughening of nacre. I know that a lot of research groups including my group have been following this new concept and mechanism. 

Henry Tan's picture

Zhigang and Xiaodong,

To my understanding, surface nanoasperities of nacre's aragonite platelets contribution to the inelasticity and ductility only when the load applied is slow or quasi-static. When nacre is under high speed impact, surface nanoasperities will break before interlamellae slip thus cause the brittle failure.

Our Mother Nature is unsuccessful in design on scenarios against high speed impact. All biological beings are weak before a bullet shot. Warfare has been totally changed since the invention of gun.

Xiaodong Li's picture

Thanks Henry. Our recent paper, shown below, reported that aragonite nanoparticles in individual nacre's platelets can rotate under loading. The nanoparticle rotation is one of the prominent mechanisms contributing to energy dissipation in nacre. The biopolymer spacing between the nanoparticles facilitates the nanoparticle rotation

X. D. Li, Z. H. Xu, and R. Z. Wang, "In-situ Observation of Nanograin Rotation and Deformation in Nacre," Nano Letters, 6 (2006) 2301-2304 .

Henry Tan's picture

Thanks Xiaodong for the very interesting paper.

Combing your discovery with previous understanding, I summarize the following mechanisms that contribute to the toughness of nacre:
1. Deflecting cracks at the aragonite platelet level
2. Unfolding the cohesive binding of the organic matrix
3. Through inter-lamellae slip
4. Through the formation of dilatation band at inter-platelet level
5. Viscosity of aragonite platelets due partly to the water in nanograin interfaces
6. Through the rotation of nanoparticles in aragonite platelets
7. Through the deformation of nanoparticles in aragonite platelets

I have a question: which mechanism contributes more to the toughness?

Xiaodong Li's picture

Thanks Henry for summarizing the 7 toughening mechanisms. I would like to add interlocking between neighboring aragonite platelets via surface nanoasperities to your list. For your question -" which mechanism contributes more?", this needs an integrated effort of experimental and modeling work. I have a mini review article on toughening mechanisms published in JOM (see below). I believe that more toughening mechanisms will be discovered and added to your list in the near future.

X. D. Li, "Nanoscale Structural and Mechanical Characterization of
Natural Nanocomposites: Seashells, " JOM, 59 (3) (2007) 71-74.

Henry Tan's picture

The interlocking may contribute to the toughness, but is may also cause stress concentration which damages the material.

Shaoxing Qu's picture

Henry, thanks for initiating this theme. A thorough understanding of the rupture process of the highly packed particulate composites is especially important in the energy field of oild drilling. How to The improve the drilling efficiency with hard rocks in some regions is a key problem. The deformation process under extreme loading conditions (high pressure, high strain rate, etc) of this kind of composites is highly required at least in China.

Henry Tan's picture


Not only in China, this is also of high priority here in North Sea oil and gas industry.

BP money spend on drilling is about one third of BP’s exploration and production sector’s total capital expenditure. Over the past few years, BP’s continuously improving performance in drilling and completing oil and gas wells has placed the company at the forefront of the industry.

Matt Lewis's picture


I'm really glad you sponsored this journal club selection.  I am working on getting a copy of the Gould, Porter, and Cullis paper as the mechanical response of energetic materials is of great interest to me. 

Karel Matous and I are sponsoring a minisymposium at the US National Congress on Computational Mechanics (11) next summer titled "Mechanical Constitutive Modeling of Energetic Materials."  The description follows:

Developing realistic mechanical constitutive models for practical energetic materials (solid propellants and explosives) is a significant challenge.  These materials typically are particulate composites.  They also include large volume fractions (usually greater than 80%) of particulate phases.  These materials usually exhibit a very small (or possibly nonexistent) range of linear mechanical response.  These materials may contain more than one particulate phase.  These phases often have high contrast in their mechanical properties over relevant ranges of pressure, strain rate, and temperature.
This minisymposium will be focused on these materials and computational and theoretical methods for developing mechanical constitutive models for them.  Papers that incorporate mechanisms characterized experimentally either on a composite system or a particular constituent are of particular interest.  Modeling approaches that address the multiple length scales seen in energetic materials are also desired.

Matt Lewis
Los Alamos, New Mexico

Henry Tan's picture

Thank you Matt,

Combining the Percolation Theory that Gould, Porter and Cullis (2009) developed at QinetiQ with our strength (Aberdeen and Manchester) in micromechanics modelling, X-ray tomography test and Material Point Method simulation, we are looking at the debonding and networking of interfaces in energetic materials.

Interface debonding in plastic bonded explosives can be gradual or involve a sudden jump, depending on material properties, composite composition and the loading type. Furthermore, the networking of debonded interfaces can also be in different modes: gradual or sudden.

It is natural to describe interface networking, similar to the process of a fluid flow percolating through a porous medium, using the percolation theory. The difference between interface networking and fluid percolating is that interface debonding can be in a gradual or sudden fashion, while fluid-structure interaction is smooth. We are combining the percolation theory and the micromechanics modelling together to describe the constitutive behaviour of highly packed particulate composites.

Henry Tan's picture

The discussions of the first week touched upon four highly packed particulate composites: nacre, sedimentary rocks, bamboo and energetic materials. Mechanisms for toughness in nacre and bamboo are of special interests with many publications by Professor Xiaodong Li of the University of South Carolina. Professor Zhigang Suo of the Harvard University mentioned the contribution of surface nanoasperities of nacre's aragonite platelets (interlock) to the toughness during slow loading rate; however, these surface nanoasperities may cause brittle failure during high rate loading. Dr. Matt Lewis of the Los Alamos National Laboratory also mentioned the high contrast in mechanical properties of other highly packed particulate composites, energetic materials including solid propellants and plastic bonded explosives, over relevant ranges of strain rate. Professor Shaoxing Qu of the Zhejiang University mentioned the importance of sedimentary rocks, another highly packed particulate composite, in petroleum industry.

Henry Tan's picture

In the summer of 2011, I was invited to give presentations at several university seminars and an international conference on the topic of “Mechanical Behaviour of Highly Packed Particulate Composites (HPPCs)”. The following are the slides I used.

1.    Microstructures of Highly Packed - Particulate Composites (HPPCs) ;
2.    Interface Cohesive Law;
3.    Network Formation and Percolation Modelling;
4.    Material Point Method Simulation and X-Ray Tomography Scanning;
5.    Catastrophic Behaviour under Loading.

Henry Tan's picture



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