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A dynamic load superposed on a static pre-load is a key problem in deep underground rock engineering projects. Based on a modified split Hopkinson pressure bar test system, the notched semi-circular bend (NSCB) method is selected to investigate the fracture initiation toughness of rocks subjected to pre-load. In this study, a two-dimensional ANSYS finite element simulation model is developed to calculate the dimensionless stress intensity factor. Three groups of NSCB specimen are tested under a pre-load of 0, 37 and 74 % of the maximum static load and with the loading rate ranging from 0 to 60 GPa m 1/2 s -1 . The results show that under a given pre-load, the fracture initiation toughness of rock increases with the loading rate, resembling the typical rate dependence of materials. Furthermore, the dynamic rock fracture toughness decreases with the static pre-load at a given loading rate. The total fracture toughness, defined as the sum of the dynamic fracture toughness and initial stress intensity factor calculated from the pre-load, increases with the pre-load at a given loading rate. An empirical equation is used to represent the effect of loading rate and pre-load force, and the results show that this equation can depict the trend of the experimental data. Keywords Fracture toughness Á Pre-load Á SHPB Á NSCB Á FEM List of symbols BD Brazilian disc ISRM International Society for Rock Mechanics CCNSCB Cracked chevron notched semi-circular bend NSCB Notched semi-circular bend SHPB Split Hopkinson pressure bar a The length of the notched crack of the NSCB specimen A 0The cross-sectional area of the bar BThe thickness of NSCB and CCNSCB specimen E 0The Young's modulus of the bar material f D The scale factor of dynamic fracture toughness over the static fracture toughness f Dp The scale factor of dynamic fracture toughness with pre-load over the static fracture toughness K I The stress intensity factor for mode-I fracture in NSCB specimen K IcThe quasi-static fracture toughness K IdThe dynamic fracture toughness K I_totalThe total fracture toughness K I_preThe stress intensity factor due to the pre-load P 1The forces at the incident end of the specimen P 2The transmitted end of the specimen P dynamicThe dynamic load P maxThe maximum value of the load P preThe pre-load P totalThe total load P(t)The time-varying loading force RThe radius of NSCB specimen R S The radius of diamond-impregnated blade saw SThe span of the supporting pins Y(a/R)The dimensionless stress intensity factor e iThe incident stress wave & Kaiwen Xia

A wideband cylindrical dielectric resonator antenna (CDRA) loaded with an annular column, namely the LCDRA, is proposed and analyzed. The antenna comprises two components an inner cylindrical dielectric and a loaded concentric column dielectric. The proposed antenna is centrally fed by a coaxial probe, and has a low profile of 0.175 λ0 (λ0 is the wavelength of the center frequency). Four conical radiation pattern modes (TM01δ, TM02δ, TM03δ and TM04δ modes) are excited and merged, providing an impedance bandwidth of 56% (3.14~5.56 GHz). A prototype of the proposed antenna is built and tested. Good agreement between the simulated and measured results, including the reflection coefficient and radiation patterns, is achieved. Index Terms-dielectric resonator antennas (DRAs), conical radiation pattern, wideband antennas

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