Many naturally occurring materials, such as wood and bone, have intricate porous microstructures and high stiffness and toughness to density ratios. Here, the influence of pores in a material on crack dynamics in brittle fracture is investigated. A dynamic phase field finite element model is used to study the effects of pores with respect to crack path, crack propagation velocity and energy release rate in a strip specimen geometry with circular pores. Four different ordered pore distributions are considered, as well as randomly distributed pores. The results show that the crack is attracted by the pores; this attraction is stronger when there is more energy available for crack growth. Crack propagation through pores also enables higher crack propagation velocities than are normally seen in strip specimens without pores (i.e. homogeneous material), without a corresponding increase in energy release rate. It is further noticed that as the porosity of an initially solid material increases, the crack tip is increasingly likely to become shielded or arrested, which may be a key to the high relative strength often exhibited by naturally occurring porous materials. We also find that when a pore is of the same size as the characteristic internal length then the pore does not localise damage. Since the characteristic internal length only regularises the damage field and not the strain end kinetic energy distributions, crack dynamics are still affected by small pores.

This article introduces new event data on violence against peacekeepers deployed to conflict-affected countries in sub-Saharan Africa between 1989 and 2009. While the practice of peacekeeping is often described as fraught with risk, a shortage of data has left scholars poorly equipped to study this important phenomenon. The Peacemakers at Risk (PAR) dataset records reported incidences of violence resulting in direct peacekeeping personnel fatalities, injuries and kidnappings. Information on the timing, location, outcomes and actors implicated is provided for each recorded event, including information on the nationalities of violence-affected peacekeepers. The dataset also charts reports of fatal violence by peacekeepers. This enables the study of peacekeepers’ use of force and provides a new lens for examining wider questions related to peacekeeping effects and conflict dynamics. Peace operations deployed by the UN as well as other peacekeeping actors are included, allowing for a rich dataset that reflects today’s diverse peacekeeping landscape. The PAR dataset makes possible the evaluation of reigning assumptions regarding peacekeeping intervention and risk, and allows scholars to pose research questions regarding the causes, characteristics and consequences of peacekeeper violence, within and across interventions. This article introduces the criteria and procedures guiding the data collection and presents the data. The article also highlights key patterns emerging from the dataset and identifies a number of potential applications and avenues for future research.

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