[en] Capabilities for predicting the response of rock masses to thermomechanical loadings are being developed under the Yucca Mountain Project (YMP) for the design of an underground nuclear waste repository at Yucca Mountain on the Nevada Test Site (NTS). An important ingredient in the computer codes being used is the constitutive description of the mechanical discontinuities (mostly joints, but also bedding planes and faults). This report summarizes preliminary laboratory experimental data on the compliance and the friction stress of artificial joints in Topopah Spring tuff in the air-dry, room-temperature condition. Also, data for a laboratory-induced, clean tensile fracture are given. Details of the analysis of the results are discussed in earlier reports. Therefore, the reader is urged to judiciously use data in this report, consulting the earlier documents when necessary. This report is primarily a catalogue of experiments and a summary of results; hence, little further analysis is given. Because of the exploratory nature of the investigation, a systematic data base was not developed for the variables (such as sliding velocity, amount of slip, and normal stress history) studied. The results suggest guidelines for further, more systematic, experimentation on fracture properties. It is critical to clearly understand the nature of the data and their implication; therefore, in the next section the constitutive relations for a joint are defined and the methods for their determination are explained. 15 refs., 89 figs