Grain crushing is of essential importance for understanding the mechanical behavior of granular materials such as sand, gravel or broken rock under higher pressures. In order to investigate the breakage mechanism of a single grain under different loading conditions, numerical simulations are carried out using DEM. Two different types of boundary conditions are considered to apply displacement-controlled load: loading using platens and loading by uncrushable macro-grains. A 2D crushable macro-grain is built up from a large number of micro-grains which are connected with respect to breakable parallel-bond properties. The response of the crushable macro-grain for different coordination numbers and location of the contact points is discussed. The numerical results show that the type of loading condition can influence the loading capacity and fragmentation patterns of the crushable macro-grain.