is indexed by their time variables and plotted on a timeline. We believed that this way of visualizing the evidence allows the investigators to find coherent evidence faster and more intuitively. We have performed a user test where a group of people has evaluated our prototype tool against a modern commercial computer forensic tool and the results of this preliminary test are very promising. The results show that users completed the task in shorter time, with greater accuracy and with less errors using CyberForensic TimeLab. The subjects also experienced that the prototype were more intuitive to use and that it allowed them to easier locate evidence that was coherent in time.

The forces in the ‘arms’ joining the particles in a peridynamic analysis depend upon the state of stress in the equivalent continuum and the orientation, length and density of the arms. Short and long arms carry less force than medium length arms as controlled by the weighting kernel. We introduce an intermediate step of imagining a mat of long fibres in which the fibre forces only depend upon the stress, the fibre orientation and the length of fibres per unit volume without the added complexity of the arm lengths. The effect of the arm lengths can then be considered as a separate exercise, which does not involve the continuum properties. The arm length is proportional to size of the particles and the separation of length from the state of stress allows for modelling of variable particle density in the discretisation of a problem domain, which enables computationally efficient accurate analysis. We then introduce the concept of arm elongation to fracture in order to model surface energy in fracture mechanics. This means that shorter arms have a larger strain to fracture than longer arms. Numerical implementation demonstrates that this produces a fracture stress that is inversely proportional to the square root of the crack length as predicted by the Griffith theory [1, 2].

Peridynamics is a numerical particle-based solid mechanics method that enables the simulation of brittle and quasi-brittle materials, as well as ductile materials. It allows cracking to appear spontaneously in the arms joining the particles and can therefore be used to simulate progressive fracture. In this article, we apply our version of peridynamics, which we call force flux peridynamics, to the simulation of concrete where the appearance of cracks plays an important role in the global mechanical properties. It is not difficult to modify the material parameters in peridynamics to achieve a given tensile strength or a given compressive strength. However, it is much more difficult to choose parameters which will model all the strength parameters of a material within the same model. When concrete fails in compression it may split or spall showing a complex relationship between compressive and tensile failure. We therefore set ourselves the simple task of producing a single peridynamics model which can predict the stiffness and strength behavior of concrete in standard compression and tension tests for which we chose the American Society for Testing and Materials standards for the cylinder compression test, the split cylinder test, and the modulus of rupture test. A parameter sensitivity study was performed based on the cylinder compression test to tune the key peridynamics parameters that determine the global material behavior. The compressive and tensile strengths were then determined from the combined simulation data. While the fracture modes, crack branching pattern and also the stressstrain curve show promising results, the maximum tensile strength was found to be significantly larger than physical experiments suggest. This is probably due to imperfections within real concrete at the interface between aggregate particles and cement paste and it shows that the detailed numerical modeling of the failure of concrete is highly complex with a large number of unknown material parameters.Discussion on this paper must be submitted within two months of the print publication. The discussion will then be published in print, along with the authors' closure, if any, approximately nine months after the print publication.

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