The paper presents a methodology for investigating fracture phenomena in sandstone. It shows the preparation of test specimens with a cyclic loading generated crack, control of the test specimen preparation and verification by means of x-ray microCT and digital image correlation (DIC) techniques. There are also presented tests studying tensile and fatigue characteristics of arkose sandstone used i. a. for the construction of the medieval Charles Bridge in Prague where weather induced tensile damage and failure occurred. Finally, the new methodology for pre-cracking of the specimens was verified experimentally and fracture toughness was computed.

The operational safety of oil and gas storage units is crucial, as any potential imperfections or cracks in a container wall could result in fracture. The key parameter in ensuring the integrity of oil and gas storage units is their fracture toughness. For its determination, compact tension (CT) and single-edge notched bend (SENB) specimens are commonly used. However, these specimens may lead to unnecessary conservatism in safety assessments. Single-edge notched tension (SENT) specimens, on the other hand, could be a more acceptable substitute, as they are shown to lead to less conservatism. The aim of this study was to determine the J-R curve for SENT specimens from pipe steel X65 using an experimentally determined J-R curve for CT specimens. This study was motivated by the fact that the use of the Gurson—Twergaard—Needleman (GTN) model for R-curve determination can significantly reduce the number of physical tests. Calculations were performed using the GTN constitutive model, calibrated on a CT specimen of width w = 50 mm, thickness B = 8.7 mm, and initial crack length a = 25.15 mm, used for the determination of the R-curve. The width and thickness of the SENT specimens considered in the calculations were similar to those for the CT specimens. Ideal clamping of the SENT specimens in the jaws was considered. A comparison of the SENT R-curve with the experimental CT R-curve showed that these curves were practically equidistant, with the former R-curve being superior to the latter one. The SENT R-curve has not been verified experimentally, because the physical specimens that match the models used for calculation do not meet the requirements of the related standards on specimen thickness. However, a comparison of this SENT R-curve with another SENT R-curve, published in the literature and obtained on the basis of the results of a two-parameter fracture mechanics approach, showed a very good agreement between the two R-curves.

The purpose of this article is to compare two predictive methods of J integral assessments for center-cracked plates, single-edge cracked plates and double-edge cracked plates produced from X52 and X70 steels, and a longitudinally cracked pipe produced from X70 steel. The two methods examined are: the GSM method and the J_s procedure of the French RCC-MR construction code, designated here as the FC method. The accuracy of J integral predictions by these methods is visualized by comparing the results obtained with the “reference” values calculated by the EPRI method. The main results showed that both methods yielded similar J integral values, although in most cases, the GSM predictions were slightly more conservative than the FC predictions. In comparison with the “reference” values of the J integral, both methods provided conservative results for most crack configurations, although the estimates for cracks of a relative length smaller than 1/8 were not found to be so conservative. The prediction of burst pressures for external longitudinal semielliptical part-through cracks in X70 steel pipe showed that the magnitudes of predicted burst pressures came very close to each other, and were conservative compared to FEM (finite element method) calculations and experimentally determined burst pressures.

The aim of this article is to quantify the loads exerted by heavy-duty vehicles when crossing over buried pipeline. This problem arises in connection to the question pertaining to the use of protective sleeves (casings) applied to gas pipelines in regions with increased demands on pipeline operation safety. An experiment was conducted on a test pipe section made from L360NE pipeline steel equipped with strain gauges along the pipe perimeter, measuring strains in the axial and circumferential directions. Strain measurements were taken after back-filling the pipe trench, then during vehicle crossings over the empty pipe, and again after pressurizing the test pipe with air. Strain-based hoop stresses at the surface of the empty test pipe were found to exceed 30 MPa after back-filling the trench and increased to more than 40 MPa during the vehicle crossings. Similarly, axial stresses reached extremes of around 17 MPa in compression and 12 MPa in tension. Applying internal air pressure to the test pipe resulted in a reduced net effect on both the hoop and axial stresses.

The presence of cracks in many historical objects indicates the action of external forces accompanied by internal strain gradients. This is usually a repetitive process, and damage cumulation may occur. A study of these effects requires a suitable methodology for testing historical stone that has been subjected to repeated tension strains. The chapter presents the results of a pilot experimental assessment of changes in the mechanical characteristics of sandstone due to accumulation of damage. The Young modulus and the Poisson number were investigated, using a verified methodology for testing stone in simple tension and in cyclic simple tension/compression loading. The results show that the first tension load displacement can be approximated very satisfactorily by a power function, and the optical digital image correlation (DIC) method again demonstrated its capacity and suitability for measuring the complex deformation field on porous surfaces and on naturally well-structured surfaces. The chapter further presents a methodology for investigating fracture phenomena in sandstone treated for consolidation. It shows the preparation of test specimens with a cyclic loading generated crack, control of the test specimen preparation, and verification by means of X-ray micro-CT and DIC techniques. The chapter illustrates an influence of various consolidation agents on the toughness of cracked specimens.

An investigation was made into selected mechanical properties of sandstone of Božanov mining site in Czechia using both natural specimens of the sandstone and specimens impregnated with consolidants – liquid products aimed at improving strength and durability of degraded stones. Experiments in three-point bending of notched and cracked specimens made it possible to determine (i) the quasi-static notch toughness as well as the fracture toughness of specimens when they were subjected to static loading, and (ii) the impact fracture toughness and total energy of fracture when specimens were subjected to impact loading. The results of the tests are presented and are discussed with a view to the effects of consolidants.