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The current paper is prepared with the objective of providing experimental evidence that the internal friction angle of rocks can be assessed using a scratch test with a blunt polycrystalline diamond compact (PDC) cutter. For this purpose, a comprehensive set of cutting experiments was carried out to determine the wear flat-rock friction coefficient in two limestones and one coarse-grained sandstone using state-of-the-art scratch based rock cutting equipment. Additional triaxial compression (TC) experiments were conducted on specimens of these rock formations, and a Coulomb failure analysis was conducted to independently estimate the internal friction coefficient of each specimen. The experimental results indicate that the value of internal friction angle (intrinsic rock property) derived from TC experiments is related to the apparent friction angle at the wear flat-rock interface of the blunt PDC cutter when the wear flat surface is inclined at inclination angles ranging between 0∘ to 1∘. Further, new results on one rock specimen were obtained by performing novel scratch tests with blunt PDC cutters with different wear flat properties, showing that the apparent friction angle at the wear flat-rock interface of a blunt cutting tool is significantly affected by the wear flat roughness and the wear flat material properties.HighlightsA new method was introduced to measure the internal friction angle of rock samples using rock cutting/drilling data.An extensive set of cutting experiments was conducted using different PDC blunt/worn cutters.The internal friction angle of rock specimens were obtained using triaxial compressrion (TC) tests.The internal friction angles of rock specimens were related to the apparent friction angles at the wear flat-rock interface when the wear flat surface is parallel to the rock free surafce.The wear flat properties of the PDC cutters have a significant effect on the apparent friction angle.

The pre-peak microstructure evolution of the material is crucial in determining the strength and failure scheme of the material, but is not captured by the existing shear strength parameters models which focus on post-peak stage information. Novel concepts of pseudo-cohesion and pseudo-internal friction angle that account for both the pre-peak and post-peak stage information were proposed in this study, based on the experimentally observed response of the rock mechanics parameters to an external load (the maximum principal stress). These two parameters were analytically derived as functions of maximum principal strain, with coefficients to be determined (i.e., by applying the Mohr–Coulomb criterion with these parameters to experimental data). The dependence of pseudo-cohesion and pseudo-internal friction angle on the axial strain and confining pressure was investigated. The evolution of the strength parameters was found to relate to the propagation of micro-crack developed in the loading process, as revealed by PFC2D simulations reproducing experiments. The results show that (1) analytical model characterizing the pseudo-cohesion and internal friction angle as the quadratic function of axial strain accurately reflects the mechanical response characteristics of the specimen; (2) before the residual stage, the pseudo-cohesion first increases and then decreases with increasing strain, while the pseudo-internal friction angle increases continuously; (3) for the sandstone specimens studied, the pseudo-cohesion at the peak stress increases by a gradually decreasing rate with increasing confining pressure, while the pseudo-internal friction angle at the peak stress decreases by a decreasing rate with the increasing confining pressure; (4) CPM well characterized the mechanical properties of rock under multiple confining pressures, as the total stress–strain curves and failure modes of numerical specimens reproduced the experimental results. The evolution of rock pseudo-shear strength parameters is closely related to the external load and the generation, propagation, and penetration process of rock cracks. The rock pseudo-shear strength parameters are gradually mobilized with the increasing load, and the propagating of cracks owing to the decrease of mobilizable maximum cohesion and the increase of mobilizable maximum internal friction angle.

An important parameter of the Hoek-Brown failure criterion for intact rock materials is m i , a dimensionless material constant that depends on the frictional characteristics of the component minerals. In this study a laboratory testing program was carried out in order to experimentally study the correlations between m i and two frictional parameters: (a) the sliding friction angle which is determined from direct shear tests on pre-fractured rock specimens and (b) the Mohr-Coulomb internal friction angle which is determined from triaxial compression strength tests conducted at low confining stresses. We carried out direct shear tests on rough tension joints of ten fresh, low porosity (< 5%) natural rocks, including two igneous, three sedimentary and five metamorphic under normal stresses ranged from 0 to 2 MPa and determined the sliding friction angle φ nd using peak shear stress and dilation measurements. An independent series of triaxial compression tests was conducted on intact cylindrical specimens of the same rocks at various confining pressures up to 70 MPa and the values of the internal friction angle φ i0 at low confining stresses were determined as well as the values of m i , σ ci and the principal stresses at the brittle-ductile transition. Our experimental results show that, within the used range of values of the parameters m i , φ nd and φ i0 , m i increases linearly with decreasing sliding friction angle and increasing internal friction angle. Both correlations were found to be statistically significant at a significance level of 0.001.

This study and theoretical analysis of local relaxation processes and their physicomechanical and physicochemical characteristics in uncured epoxy oligomers DER-330, ED-20, ED-16 and ED-8 were carried out in the dynamic mode of freely damped torsional oscillations excited in specimens of the investigated systems. Internal friction spectra and temperature dependences of the frequency of free damped oscillations were obtained within the temperature range covering both the solid and liquid states of the epoxy oligomers. Based on the phenomenological models of a standard linear solid and the Maxwell model, the energetic and relaxation characteristics for each local dissipative process, as well as the temperature changes in strength properties (considering the defects of the shear modulus of the relaxation process) of the system as a whole, were calculated.

The shear strength properties of rock materials, cohesion and internal friction angle, are determined by carrying out tri-axial strength test on cylindrical core specimens in laboratory. But determination of these parameters by triaxial tests in accordance with standards and suggested methods, particularly for weak, fractured and weathered rocks is exteremely difficult and/or impossible due to difficulties related to preparation of test specimens suitable for this test. In addition, the tri-axial test requires high cost equipment and too much time for sample preparation and testing. In such cases, there is a need to precisely estimate the friction angle and estimation of rock shear strength properties using some indirect methods, as they are economical and easy to carry out. In this study, the traditional method, which is recommended to be used for the prediction of internal friction angle (ϕ) when triaxial test data is not available, was briefly assessed with its some limitations and an alternative method using theoretical tensile strength and uniaxial compressive strength to predict ϕ was proposed. Then the prediction performances of traditional and proposed methods were compared using a very large data set collected from published literature. The statistical reliability of the derived equations was assessed using F- and t-tests and according to the test results the prediction equations were found to be statistically reliable. The results indicated that the method proposed in this study using the theoretical tensile strength yields best predictions of ϕ when compared to those estimated from the traditional methods based on direct and Brazilian tensile strength values.

A study was conducted on the internal friction spectra and temperature dependencies of the frequency of free damped oscillatory processes excited in the investigated samples of low-density polyethylene (LDPE) and high-density polyethylene (HDPE) over a temperature range from −150 °C to +150 °C. It was found that the internal friction spectra exhibit several local dissipative processes of varying intensity, which manifest in different temperature intervals. The structure of the internal friction spectra and the peaks of dissipative losses are complex, as evidenced by the occurrence of sharp, locally temperature-dependent jumps in the intensity of dissipative losses observed throughout the entire temperature range. A theoretical analysis was performed to explore the relationship between the anomalous change in the frequency of the oscillatory process and the defect in the shear modulus, as well as the mechanisms of internal friction for the most intense dissipative loss processes identified in the internal friction spectra. A significant difference was revealed in the structure of the internal friction spectra of LDPE and HDPE in the temperature range of −50 °C to +50 °C. A comparison of the LDPE and HDPE samples was conducted based on changes in their strength characteristics, taking into account the locally temperature-dependent changes in the shear modulus caused by local dissipative losses observed in the internal friction spectra.

A theoretical analysis has been performed for experimental data on internal friction spectra and temperature–frequency dependences obtained by the method of free damped torsional oscillations for diverse liquid hardeners (TETA, PEPA, and MTHPA) of epoxy oligomers. The main phenomenological model representations have been considered and employed to analyze various physicomechanical and physicochemical characteristics of local dissipative processes, which may have different mechanisms of internal friction (hysteresis-, phase-, and relaxation-type).

The spectra of internal friction and temperature dependencies of the frequency of a free-damped oscillation process excited in the specimens of an amorphous–crystalline copolymer of polyoxymethylene with the co-monomer trioxane (POM-C) with a degree of crystallinity ~60% in the temperature range from −150 °C to +170 °C has been studied. It has been established that the spectra of internal friction show five local dissipative processes of varying intensity, manifested in different temperature ranges of the spectrum. An anomalous decrease in the frequency of the oscillatory process was detected in the temperature ranges where the most intense dissipative losses appear on the spectrum of internal friction. Based on phenomenological model representations of a standard linear solid, the physical–mechanical (shear modulus defect, temperature position of local regions of inelasticity) and physical–chemical (activation energy, discrete relaxation time, intensities of detected dissipative processes) characteristics of each local dissipative process were calculated. It was found that the intensities of dissipative processes remain virtually unchanged for both annealed and non-annealed samples. The maximum variation in the shear modulus defect is 0.06%. Additionally, according to computational data, small changes are also characteristic of the following parameters: the activation energy varies from 0.5 to 1.4 kJ/mol and the relaxation time changes from 0.002 to 0.007 s, depending on the presence or absence of annealing. As a result of annealing, there is a significant increase in the relaxation microinheterogenity of the polymer system across the entire temperature range (250% for the low-temperature region and 115% for the high-temperature region).

With the continued expansion of waste landfills, accidents may occur if the landfills are not properly stabilized. In this study, samples of municipal solid waste (MSW) from a waste landfill in Xi'an, China were collected through on-site drilling. Considering the effects of nine landfill ages (1, 2, 3, 11, 12, 13, 21, 22, and 23 y) and six moisture contents (natural, 20, 40, 60, 80, and 100%), 324 groups of MSW were tested in the laboratory using a direct shear test apparatus. The results indicate the following: (1) with an increase in horizontal shear displacement, the shear stress of MSW gradually increases without a peak stress phenomenon, which is a displacement hardening curve; (2) with an increase in landfill age, the shear strength of MSW increases; (3) with an increase in moisture content, the shear strength of MSW increases; (4) with an increase in landfill age, the cohesion ( c ) decreases and the internal friction angle ( φ ) increases; and (5) with an increase in moisture content, the c and φ of MSW increases. The c range found in this study was 6.04–18.69 kPa, while the φ was 10.78–18.26°. The results of this study can provide a reference for stability calculations for MSW landfills.

This investigation focuses on the experimental determination of critical mechanical properties of various granular materials, namely cement, sand, wheat, granulated sugar, and wheat flour, which are essential in the design of silos. These properties, crucial for defining the behavior of materials stored in silos through numerical methods, have been less documented in existing literature. Conducted at the Research Laboratory of Civil Engineering and Hydraulics of 8 May 1945 University, Guelma, Algeria, a series of geotechnical tests, including triaxial, ring shear, and Oedometric tests, were employed to ascertain a range of properties: internal friction angle, apparent cohesion, specific weight, elastic modulus, Poisson ratio, particle-to-steel wall friction coefficient, and dilatancy angle. It was observed that sand and sugar exhibit the highest rigidity, as indicated by their elastic moduli. In terms of compressibility, sugar, wheat, and wheat flour demonstrated the greatest extent. Discrepancies between the results of triaxial and shear tests suggest a probable influence of material consolidation methods on outcomes. While certain findings aligned with previous studies, discrepancies in materials like cement and sand necessitate additional testing for verification. This study proposes recommended values for these mechanical properties, contributing significantly to the field of silo design.