ABSTRACT:

The fracturing behavior and mechanical characterization of rocks are important for many applications in the fields of civil, mining, geothermal, and petroleum engineering. Laboratory testing of rocks plays a major role in understanding the underlying processes that occur on the larger scale and for predicting rock behavior. Fracturing research, such as producing multiple fractures that follow a particular pattern, requires well-defined and consistent boundary conditions. Consequently, the testing design and setup can greatly influence the results. In this study, a comprehensive experimental program using an artificial material was carried out to systematically evaluate the effects of different parameters in rock testing under uniaxial compression. The parameters include the compression platen type, centering of the specimen, loading control method and rate, specimen size, cross-sectional geometry, and boundary constraints. The results show that these parameters have a significant effect on the mechanical behavior of rocks. Using a fixed compression platen helped reduce bulging of the material. Centering of the specimen played a critical role to avoid buckling and unequal distribution of stress. Slower displacement rates can control the energy being released once failure occurs to prevent the specimen from exploding. Larger specimens generally fail at lower stresses compared to smaller specimens. Also, the frictional end effects were investigated by comparing lubricated and non-lubricated end conditions.

1. INTRODUCTION

The knowledge of mechanical behavior of rocks is relevant and important in rock mechanics, particularly when applied to the fields of civil, mining, geothermal, and petroleum engineering (Isah et al., 2020; Almubarak et al., 2020). Laboratory testing has played an important role in characterizing the strength of rocks and understanding fracture behavior (Xu et al., 2016). As will be explained later, the investigation reported in this paper is conducted with an artificial material.

There has been an interest in using artificial model materials for as long as the mechanical testing of rocks has been performed. Rapid prototyping (RP), additive manufacturing (AM), and three-dimensional printing (3DP) are three interchangeable terms that define a set of methods for the fast, precise, and repeatable production of elements (Zhou and Zhu, 2018). The technology was first introduced in the 1980s and is based on the process of joining materials layer-by-layer to form an object using computer-aided design (CAD). Polymeric, metallic, ceramic, and even complex composite components are among the materials used (Ngo et al., 2018). Various 3DP techniques have been developed, including fused deposition manufacturing (FDM), stereolithography (SLA), and selective laser sintering (SLS).

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