Damage Zone Research Articles

Analytical model for predicting localized damage in RC beams under contact explosion

The determination of damage to reinforced concrete (RC) beams when buildings are exposed to explosives is critical for assessing building destruction and overall stability. However, a well-established theoretical framework for determining the damage of RC beams under contact explosion is currently lacking. In this study, we developed an analytical model to determine the size and shape of the local damage zone in the RC beam subjected to contact explosion. The model analyzes the evolution of damage in the RC beam, considering the function of steel reinforcement and calculating the damage zone. Experimental investigations were conducted using various weights of explosives to study the damage caused by contact explosions on RC beams. By comparing the model with the experimental results, the average error of the analysis model was found to be 9.0 %, providing an accurate calculation of local damage in RC beams and an effective reflection of the dynamic response process. Consequently, these research results can be further used to assess the residual load-bearing capacity of damaged RC beams and predict the extent of damage.

EXPERIMENTAL STUDIES OF A DAMAGED BEAM REINFORCED WITH FIBER CONCRETE

The paper presents the results of a study of the load-bearing capacity of a beam damaged during hostilities, which was reinforced with steel fiber concrete. A beam with 20% damage in the compressed zone is considered. Before concreting, a foam liner was installed in the area of the planned damage, the shape and dimensions of which corresponded to the planned damage. After the concrete gained 70% of the brand strength, the liner was removed, and the resulting cavity was filled with a 2% mixture of fiber-reinforced concrete. This is one of the options for strengthening a beam in a comprehensive testing program for damaged beams, which involves studying a series of beams with different types of damage, damage zone (tension and compression) and its size, geometry and method of strengthening. The authors have developed a special stand for testing. Plane transverse bending of the loading of the beam under test is created using a hydraulic jack and a metal I-beam with a traverse that transmits two equal concentrated forces to the beam. The created load is controlled by an exemplary dynamometer of the Tokar system and a ring dynamometer, which acts as a support. Experimental studies have shown that a beam, the cross-section of which is 20% damaged in the middle compressed zone, and the shape of the damage is close to rectangular, has a load-bearing capacity of 93.6 kN, which is 95.0% of the load-bearing capacity of an undamaged beam (98.5 kN). Crack formation began on the 5th stage of loading, when the load value was 32.5 kN, that is, 34.7% of the load-bearing capacity of the damaged beam. In this case, 4 cracks formed in the pure bending zone. At the sixth stage, three more cracks appeared. At stages 9, 10 and 14 of loading, 7 more cracks formed. The maximum final crack opening width was 0.8 mm. throughout the testing process, the fiber-reinforced concrete liner worked with the beam as a single unit. It can be argued that strengthening a beam with 20% damage in the compressed zone using the method considered in the work makes it possible to achieve its load-bearing capacity, which is 95% of the load-bearing capacity of an undamaged beam.

Study of a Tailings Dam Failure Pattern and Post-Failure Effects under Flooding Conditions

Tailings dams are structures that store both tailings and water, so almost all tailings dam accidents are water related. This paper investigates a tailings dam’s failure pattern and damage development under flood conditions by conducting a 1:100 large-scale tailings dam failure model test. It also simulates the tailings dam breach discharge process based on the breach mode using FLOW-3D software, and the extent of the impact of the dam failure debris flow downstream was derived. Dam failure tests show that the form of dam failure under flood conditions is seepage failure. The damage manifests itself in the form of flowing soil, which is broadly divided into two processes: the seepage stabilization phase and the flowing soil development damage phase. The dam failure test shows that the rate of rise in the height of the dam saturation line is faster and then slower. The order of the saturation line at the dam face is second-level sub-dam, third-level sub-dam, first-level sub-dam, and fourth-level sub-dam. The final failure of the tailings dam is the production of a breach at the top of the dam due to the development of the dam’s fluid damage zone to the dam top. The simulated dam breach release results show that by the time the dam breach fluid is released at 300 s, the area of over mud has reached 95,250 square meters. Local farmland and roads were submerged, and other facilities and buildings would be damaged to varying degrees. Based on the data from these studies, targeted measures for rectifying hidden dangers and preventing dam breaks from both technical and management aspects can be proposed for tailings dams.

Biosensing with Tailored Track-Etched Nanochannels

Inspired by the high sensitivity, efficiency and selectivity of biological ion channels, the development of solid-state nanochannel sensors has been at the forefront of nanotechnology research in the last years. Many researchers worldwide have concentrated their efforts on the development of artificial nanochannels that can mimic the features of biological ion channels. These synthetic nanostructures are based on abiotic materials which provide higher robustness, thermal stability, chemical versatility and mechanical resistance than their biological counterparts. Furthermore, synthetic nanochannels and specific surface functionalization strategies have enabled fine control over the geometry and charge distribution which yielded the ability to manipulate the flux of ions through the channel. This gave rise to the formation of nanochannel-based platforms with applications in (bio)sensing as well as other fields. The development of chemical- and biosensors requires a combination of reliable nanofabrication techniques and versatile surface modification strategies, which render high sensitivity and high selectivity, respectively [1].Tailored single polymer nanochannels are routinely fabricated by ion-track nanotechnology. Polymer films are first irradiated with individual swift heavy ions at the GSI UNILAC accelerator. Each ion generates a highly localized cylindrical damage zone along its trajectory. These so-called ion tracks are subsequently dissolved and enlarged in a chemical etching process. By selecting suitable etching conditions, geometry (cylindrical, conical or bullet-like) and size of the nanochannels can be adjusted. The nanochannel surface can then be functionalized by means of different chemical strategies to enhance the sensing capabilities.There are two main nanochannel sensing techniques, ion current rectification (ICR) and resistive-pulse sensing (RPS). Both are affected by the geometry and surface charge of the nanochannel and based on measuring the change in ion current flowing through the channel induced by the chosen analyte [2]. In both approaches, the presence of a target analyte triggers a variation in the physicochemical properties of the channel which can be related to measurable changes in the transmembrane current, and is proportional to the analyte concentration.In this contribution, we will present nanochannel sensing platforms based on several single polymer channels fabricated by ion-track nanotechnology and a selection of surface functionalization strategies applied to the nanochannels. We will then discuss selected examples recently obtained with these tailored functionalized nanochannels and demonstrate selective and sensitive sensing applications based on both the ICR and RPS phenomena.[1] Toum Terrones, Y., Cayón, V. M., Laucirica, G., Cortez, M. L., Toimil-Molares, M. E., Trautmann, C., ... & Azzaroni, O. (2022). Ion Track-Based Nanofluidic Biosensors. In Miniaturized Biosensing Devices: Fabrication and Applications (pp. 57-81). Singapore: Springer Nature Singapore.[2] Kaya, D., & Keçeci, K. (2020). Track-etched nanoporous polymer membranes as sensors: A review. Journal of The Electrochemical Society, 167(3), 037543.

Evolution of an earthquake-induced landslide complex in the South Island of New Zealand: How fault damage zones and seismicity contribute to slope failures

Abstract Tectonic deformation within fault damage zones can influence slope stability and landslide failure mechanisms due to rock mass strength effects and the presence of tectonic structures. Here, we used detailed site investigations to evaluate controls on deformation within the Half Moon Bay landslide complex, located ~1 km from the surface trace of the Hope fault in the South Island of New Zealand. During the 2016 Mw 7.8 Kaikōura earthquake, the slope experienced up to ~13 m of displacement and partially transitioned into a rock avalanche (with a volume of ~350,000 m3). Deep-seated deformation of the entire slope predated the 2016 earthquake. Results of geomorphological analysis, field mapping, geophysical surveys, slope displacement, and a 60-m-deep borehole in the incipient portion of the landslide indicated the presence of a subvertical tectonic fabric and intense fracturing and weathering of the rock mass, which gradually decrease with depth. Based on these results, we established a conceptual model wherein the landslide failure mechanism is a combination of flexural toppling along the subvertical structures coupled with joint-step-path sliding along preexisting, closely spaced discontinuities within the graywacke rock mass. Coseismic slope displacements revealed a large area of incipient failure behind the headscarp of the 2016 rock avalanche, which will likely result in further avalanching at the site. This case study demonstrates that inherited tectonic structures (combined with seismicity and weathering in an oversteepened coastal slope) play an important role in the evolution of hillslopes near active faults.

Monitoring Technology of Surrounding Rock Deformation Based on IWFBG Sensing Principle and Its Application

Abstract To address the challenge of achieving precise real-time monitoring of significant deformation in deep roadway surrounding rock, a quasi-distributed strain-sensing cable (SSC), which has a spatial resolution of 1 m, was developed based on the principle of Identical Weak Fiber Bragg Gratings. The performance of SSC has been evaluated through a series of calibration tests, revealing a range of 0%–3%, an accuracy level of 0.5%, a strain sensitivity measuring at 1.23 pm/με, and a temperature sensitivity recorded as 10.78 pm/℃. Furthermore, a real-time deformation monitoring system has been established to monitor rock deformation, consisting of SSC, supporting installation equipment, demodulation equipment, and monitoring software. Moreover, the proposed methodology was applied in the deep roadway of Guqiao coal mine. The results showed that the maximum surface displacement of the roadway is 103.47 mm, while the lateral contrast error stands at 5%. The maximum strain value of the surrounding rock measures 27,095 με. The depth of rock rupture zone is about 3 m, while the boundary of rock damage zone extends up to 6 m. This information serves as the foundation for determining the parameters of the roadway reinforcement support design.

Evaluation of the effectiveness of the use of indicator methods in determining the carbonization of concrete

Currently, one of the most important problems is the impact of aggressive environments on reinforced concrete structures, as a result of which the process of their destruction is triggered. One of the reasons for the failure of reinforced concrete structures is the process of carbonization of concrete. In practice, in order to timely eliminate and prevent the problem of carbonization of concrete, an indicator method for determining damaged zones is used. However, the traditional phenolphthalein test method does not allow to determine with high accuracy the boundary zones of concrete that are most vulnerable to carbonization. The article discusses the possibility of improving the phenolphthalein test method by using additional solutions of acid-base indicators alizarin and neutral red. The results of experiments on measuring the surface neutralized layer of concrete with alcohol solutions of acid-base indicators alizarin and neutral red on concrete samples of various ages and sizes are presented. The results of a comparative analysis of the traditional and improved methods for determining the carbonization of concrete are presented. The method proposed by the authors is distinguished by greater accuracy of the results obtained. The solution of neutral red expands the boundaries of the application of the phenolphthalein test method for determining the carbonization zones of concrete at 6 < pH < 10.5. The use of alizarin in addition to the phenolphthalein solution is difficult because the indicator solution is too dull in color, resulting in the definition of zones of highly alkaline concrete not being accurate enough. Due to the fact that the phenolphthalein test method has limitations in its use by examiners at the field stage, it is advisable to continue the search for indicators that can supplement or fully replace phenolphthalein for these purposes.

LVI and CAI Analysis of Woven Carbon Fiber Reinforced Composite Laminates with Different Stacking Sequence

The study investigates LVI testing on woven carbon fiber-reinforced composite laminates at three different energy levels and assesses the specimens for their compressive strengths. X-ray CT scans are used to study the damaged envelopes, which allows better insights into the damage progression and failure mechanisms of the composite. The study investigates how post-impact damage propagation is influenced by alterations in impact energy and stacking orientation. The findings demonstrated that several variables, such as the characteristics of the constituent materials, the stacking order, laminate thickness, and ply orientations, had an impact on the CAI strength of the composite laminate. These findings highlight the importance of considering multiple factors when designing composite materials that can withstand impact loading and maintain their structural integrity. Even in specimens showing barely perceptible surface damage, a considerable drop in compressive strength is seen after the LVI testing. When specimens are struck with 25 J of energy, the compressive strength reduction reached a maximum value of 15.68%. In CAI testing, it is typical for sub-laminates to buckle near the impact-induced damage zone, resulting in failure. The magnitude of impact damage area can significantly affect the CAI strength, as the damaged area may create a stress concentration that can lead to buckling or other types of failure. Therefore, it is important to consider the impact energy and damage size when evaluating the CAI strength of composite materials.

Fatigue failure prediction method and constant amplitude equivalence strategy of adhesive interface under variable amplitude loading

The existing commercial software can only predict the fatigue life of homogeneous materials/structures under constant amplitude loading. This work developed a software tool that could predict the fatigue life of the adhesive interface under variable amplitude loading by embedding a modified fatigue cohesive zone model and amplitude variation function. Central to this innovation is the load sequence effect factor (γ), designed to consider nuanced influences like the shock effect of stepped amplitude changes on the fatigue properties. The effects of the block loading sequence on the fatigue life and crack growth rate of the adhesive interface were investigated numerically, and the influence of stepped amplitude on the evolution of a damage zone ahead of the main crack front was observed. It was found that the loading sequence from Low to High (L-H) accelerated the crack growth rate and reduced the fatigue life, and vice versa. Under the same fatigue life, a constant amplitude fatigue equivalence (CAFE) strategy is proposed, which could convert a variable amplitude road spectrum into a constant amplitude load more suitable for the testing bench. The proposed tool and method are also suitable for bi-material interface failure prediction under variable amplitude fatigue loading.

Direct assessment of the hydraulic structure of the plate boundary at the toe of the Nankai accretionary prism

SUMMARY The Nankai Trough is a locus of slow slip, low-frequency earthquakes, and large magnitude (Mw > 8) earthquakes. It is usually assumed that high pore pressure contributes substantially to earthquake dynamics. Hence, a thorough understanding of the hydraulic regime of the Nankai accretionary prism is needed to understand this diversity of behaviours. We focus on the toe of the accretionary prism by studying data from Hole C0024A, part of the Nankai Trough Seismogenic Zone Experiment (NanTroSEIZE) project, that intersected the décollement at 813 m below seafloor (mbsf) about 3 km away from the trench. We contribute to this understanding by innovatively integrating drilling and logging data to derive high-resolution hydraulic profiles along the borehole. A quantitative re-analysis of the variation in the downhole annular pressure monitored during drilling show localized fluid flow from the formation to the borehole in excess of 0.05 m3 s−1, especially in the damage zones at the footwall of the décollement. To validate the fluid flow profile, pore pressure was estimated independently from empirical relationships between pore pressure, porosity and P-wave velocity, obtained from consolidation experiments and Eaton-type methods based on drilling or sonic velocity data. The formation fluids are becoming significantly overpressurized with depth in the few hundred metres above décollement. The hydraulic profile suggests that the core of the décollement acts as a barrier inhibiting upward fluid convection, whereas the damage zone acts as an efficient longitudinal channel able to diffuse high pressure from the deeper part of the subduction.

Effect of low dosage fiber reinforcement on cracking performance of asphalt concrete

Fiber reinforcement is one of the methods used to improve cracking resistance of quasi-brittle materials such as asphalt concrete (AC). Despite the widespread use of fibers in AC, there is a lack of fundamental understanding of fracture behavior of fiber reinforced asphalt concrete (FRAC). The main goal of this research is comprehensive fracture characterization of low dosage applications of two synthetic fibers (polyethylene-aramid and nylon) and understand the performance bias of low dosage fiber reinforcement at mixture level in different test conditions. Two laboratory prepared mixtures (fine and coarse-graded) were designed with consistent volumetrics. Two crack mouth opening displacement (CMOD) – controlled experiments (SCB-CMOD and DCT) were performed to facilitate a controlled crack propagation at low and intermediate temperatures. Alternative load-line displacement (LLD) control cracking tests (I-FIT and IDEAL-CT) with different geometries, testing parameters, and loading modes were also evaluated. It was observed that the mixes with nylon fibers had a distinctive and better fracture response in all of the experiments. Some improvements were observed with aramid fiber configuration dependent on the test performed and mixture type. The key test features that resulted in more distinction between the low dosage fiber mixes and the control appeared to be ligament length, affected damage area, and cracking patterns observed in the experiments. The tests with larger ligament length (i.e., larger affected damage zones) were sometimes visible with more tortuous cracking patterns with many branches resulted in more consistent and noticeable outcomes with the fibers. Further research is needed to identify potential test bias and develop an ideal test protocol and test geometry that can objectively evaluate the performance of low dosage fibers.

Petrological Evolution and Mass Redistribution in Basaltic Fault Zones: An Example From the Faroe Islands, North Atlantic Igneous Province

AbstractFault rock petrology exerts an important influence on the permeability structure and mechanical properties of fault zones. Slip‐related deformation on upper‐crustal faults in basaltic rocks is closely associated with fluid‐rock interaction, altering the distribution of physical properties within the fault. Here, we present quantitative descriptions of the geochemical and petrological evolution of basalt‐derived fault rocks from three passively exhumed fault zones in the Faroe Islands. Fault‐rock petrology is determined by optical petrography and automated phase identification based on micrometer‐scale chemical maps from scanning electron microscope X‐ray spectroscopy. Geochemical evolution is assessed from major and trace element composition measured by X‐ray fluorescence. The fault rocks show intense fluid‐mediated alteration from a tholeiitic basalt protolith in the damage zones, and mechanical mixing in the fault cores. Pervasive alteration occurs early during fault zone evolution, with incipient fault damage increasing permeability and allowing along‐fault percolation of carbonated meteoric water, increasing fluid‐rock ratios. Our results suggest that the only mobile species within the fault zones are Ca, Si, and Al, which are leached during the hydrolysis of volcanic glass and plagioclase, and CO2, which is added by percolating waters. These species are transported from the damage zones into the fault cores, where they precipitate as zeolite and calcite cement in veins and hydrothermal breccias. We propose that solutes are replenished by cement dissolution through pressure‐solution during cataclastic creep, during repeated cycles of hydrofracture and cementation. The fault zones are natural reactors for fluid‐mediated alteration by CO2 and water, while other species are redistributed within the fault zones.

Restoration of the service and loss minimization in electrical distribution systems

<p>Restoration of service during faults to healthy zones and the minimization of true or real power losses are the main aspects of the satisfactory operation of an electrical distribution system (EDS). These objectives can be achieved with artificially intelligent optimisation techniques through electrical distribution system reconfiguration. The restoration of service is an important part of ensuring a stable power supply. If there is a fault with the EDS, the damaged zone is separated, and the healthy system is restored without breaching limitations. In the distribution system, ohmic losses are 25-35%. It is essential to reconfigure the system toreduce these losses. In this paper, a hybrid artificial rabbits’optimisation and improved mayfly optimisation (ARO-IMO) technique is adopted for restoration of serviceand loss minimization. The method being suggested will be carried out on an IEEE 4-feeder network for restoration of service and on IEEE 33 and69 radial distribution networks (RDN) for diminution of losses.</p>

Model of fractured medium and nondestructive control of composite materials

Non-destructive testing of composites is an important issue in the modern aircraft industry. Composites are susceptible to the barely visible impact damage which can affect the residual strength of the material and occurs both during production and operation. The continuum model for describing the damaged zone is presented. The slip theory relations used for a continuous distribution of slip planes are applied. At the initial stage, the isotropic background model is used. This model allows the material slippage along the fractures based on the Coulomb friction law with the small viscous addition. In this regime, the govern system of equations becomes rigid. To overcome this difficulty, the explicit–implicit grid-characteristic scheme is proposed. The standard ultrasound diagnostic procedure of damaged composite materials is successfully simulated. Compared with the trivial free-surface fracture model, different reactions on the compression and stretch waves are registered. This approach provided an effective way for the simulation of complex dynamic behavior of damage zones.

FIRING EFFICIENCY OF ANTI-AIRCRAFT MISSILE COMPLEX “STRILA-10” IN TARGET DETECTION THROUGH THE OPTICAL VISOR AND AUTOMATED TARGET POINTER

When preparing for and conducting combat operations of the “SA-13 Gopher” anti-aircraft missile system, commanders and combat personnel of the system must know the missile firing efficiency indicators [1–4]. As an indicator of missile firing efficiency, the probability of hitting a target with one missile is usually used. Massive homing is carried out via the contrast channel or the infrared channel of the missile homing head. Under various conditions of use, it is necessary to evaluate the detection ranges that are realised and the probability of timely target detection, launch range and missile launch probability. It is also necessary to imagine the possible values of the inclined distances to the far edge of the kill zone of the complex. The probability of hitting a target with a single missile is affected by the geometric dimensions of the targets, their colour and contrast in the infrared wavelength range, the presence of target designation, meteorological range of visibility etc.
 The task of determining the firing efficiency of the “SA-13 Gopher” anti-aircraft missile system when detecting targets through the optical sight and automated targeting is therefore relevant and important.
 Research presented in the published [1–4; 12–13] do not allow determining the value of the probability of hitting different air targets in various conditions of the complex’s use. This literature provides only general approaches to solving this problem for typical conditions of use of an anti-aircraft missile system. A numerical modeling technique for determining the firing efficiency indicator in the form of values of the probability of hitting targets by a missile has been developed. The modeling took into account the speed of the targets, their plane in the shooting picture, their radiating capabilities and meteorological visibility range, the quality of the combat work of the operators of the combat vehicle, the sun exposure and the closing angles of the combat vehicle. Found possible detection ranges and detection probabilities of a typical target and a small unmanned aerial vehicle (UAV). A high probability of the operator of a combat vehicle missing a typical target at low and medium flight altitudes was noted. Considered launch ranges of missiles that are implemented and the probability of launching a missile when targets are captured in the contrast and infrared channels of the homing head. The largest inclined ranges to the far boundary of the zone of damage of the complex were calculated. The values of the probability of hitting a typical target and UAV in various firing conditions are determined. Sufficient firing efficiency has been proven when capturing and launching a missile in the contrast guidance channel and firing at a typical target. A comparison of the contrast and infrared channels of the homing missile head when firing at UAVs was carried out. Analytical expressions for the calculation of missile firing efficiency indicators and corresponding graphic material are presented.

Effect of Solidified Depth on the Vertical Compressive Bearing Characteristics of the Soil Continuously Solidified Pile Group Foundation

To meet the ultra-high bearing capacity design requirements of pile foundations under geological conditions without a good holding layer, we invented a new type of group pile foundation with the soil continuously solidified between piles (hereinafter referred to as the SCS group pile foundation). Considering the solidified depth as a key influencing factor, the vertical ultimate compressive bearing capacity, load transfer law, and damage pattern of the soil around the continuously solidified group pile foundation were investigated using an indoor half-model test. The results revealed that the setting of the continuously solidified part has a significant effect on its compressive bearing characteristics. The ultimate compressive bearing capacity of the SCS group pile foundation was increased by four to nine times compared with the traditional group pile foundation. When the pile spacing is 4–6D (D = pile diameter), designing a continuously solidified depth greater than 14D is recommended. Except for the solidified depths of 2D and 18D, the lateral resistances of the other model piles first increase and then decrease with increasing depth. The maximum values were located at the continuously solidified part and were obviously larger than those of the other pile sections. The maximum pile lateral frictional resistance was provided at the maximum depth of the continuously solidified part. After setting up the continuously solidified part, none of the bearing capacity of the pile ends exceeded 5%. The bearing capacity of the SCS group pile foundation was mainly shared by the continuously solidified part and the pile lateral frictional resistance. For the same pile spacing, the high strain damage zone of the soil at the bottom of the continuously solidified 2D–14D foundation was “abacus bead”; when the burial depth of the continuously solidified part reached 18D, the foundation soil exhibited “inverted bowl” damage.

Fracture development around wellbore excavation: Insights from a 2D thermo-mechanical FDEM analysis

Insights into fracture development and excavation damaged zone (EDZ) formation around wellbore excavation sites are essential for understanding wellbore stability. In this study, a novel thermo-mechanical scheme is implemented in the 2D combined finite-discrete element method (FDEM) to investigate the fracturing process around a wellbore in a high-temperature subsurface environment. The developed scheme captures the isotropic/anisotropic thermal conduction characteristics within the rock formation. The coupled scheme and stress distributions around the wellbore subject to in-situ stress, drilling mud pressure, and temperature changes are validated by closed-form solutions. Fracture development and progressive EDZ formation by various mechanisms are analyzed. The results show that for an unsupported wellbore, fractures initiate in the region of the most severe stress concentration due to excavation unloading and constitute an EDZ that resembles the logarithmic-spiral rupture zone captured by experimental observations and Mohr-Coulomb models, resulting in potential water inrush due to the significantly increased fracture transmissivity of the EDZ and wellbore collapse. The shape and extent of the EDZ for wellbore excavation in the layered rock mass are dominated by the stress redistribution and the presence of low-strength bedding planes favorably oriented for bedding slippage. The excavation unloading-induced stresses can be effectively counteracted by properly applying drilling mud pressure, and the disturbance of the stress field occurs only within a small region, greatly reducing the extension of the EDZ. Thermal contraction of the surrounding rock due to its convective interaction with the cold drilling mud induces extra fractures around the wellbore. The extension of the EDZ is greater with increased thermal expansivity of the rock formation. Overall, the results indicate that the adopted thermo-mechanical FDEM simulation can provide unique geomechanical insight into wellbore stability behavior analysis, in which explicit consideration of the fracturing and fragmentation processes is of great significance.

BEARING CAPACITY OF A BEAM DAMAGED DURING COMBAT ACTIONS STRENGTHENED WITH THE USE OF FIBER CONCRETE

The paper presents the results of a study of the load-bearing capacity of a beam damaged during hostilities, which was reinforced with steel-reinforced concrete. A beam with 20 percent damage in the compression zone is considered. Before concreting, a foam insert was installed in the area of the planned damage, the shape and dimensions of which corresponded to the planned damage. After the concrete was set to 70% grade strength, the liner was pulled out, and the resulting cavity was filled with a 2% mixture of fiber concrete. This is one of the beam strengthening options in a comprehensive damaged beam testing program, which involves the study of a series of beams with different types of damage, varying damage zone (tensile and compression) and its magnitude, geometry and method of strengthening. The authors developed a special stand for testing. The load-bearing capacity of the damaged beam reinforced with fiber concrete was 80.6 kN, or 89.5% of the load-bearing capacity of the intact beam. Cracking started at the 4th load stage, when the load value was 16.1 kN, or 20% of the bearing capacity of the damaged beam. At the same time, 10 cracks formed in the zone of pure bending, the opening width of which did not exceed half the price of the microscope division, which is 0.005 mm. At the next eight stages of loading (up to 48.4kN), no new cracks were observed, and the width of the opening of all the ones that had previously formed doubled - it reached 0.01mm. At the 12th, 13th and 19th stages of loading, 4 more cracks appeared. The maximum final crack opening width was 1.2 mm. Up to a load of 68.5kN, which is 85% of the load-bearing capacity of the damaged beam, the reinforced concrete liner works with the beam almost as a unit, and then the compressed zone of concrete squeezes out the liner. It is claimed that the strengthening of a beam with 20% damage in the compressed zone in the manner considered in the work allows to achieve its bearing capacity, which is almost 90% of the bearing capacity of an undamaged beam.

Performance and mechanisms of ultraviolet laser ablation of plain-woven CFRP composites

Plain-woven carbon-fiber-reinforced-polymer (CFRP) composites prove advantageous in designing and manufacturing aeronautic and aerospace structures due to their excellent mechanical properties. Their harsh service environment usually leads to aircraft surface pits, scratches, and other types of defects, which result in internal damages that reduce their strength, influencing their safety and reliability. With laser-controlled ablation, surface damage removal was implemented. However, the multiscale characteristics of plain-woven CFRP (macroscopic plain-woven textiles, mesoscopic fiber clusters, together with microscopic fiber and epoxy resin) lead to complex thermal–mechanical ablation action, prone to secondary surface damages and resin residue. Aiming at the requirement of high-performance removal of the damaged zone, a comprehensive investigation of the influence of laser ablation strategies, including the wavelength, defocus distance, scanning speed, hatch distance, scanning passes, etc., on generating morphologies was conducted. Results identified that the severe anisotropy of plain-woven CFRP gained a wide heat-affected zone (HAZ), which was restrained by adopting an ultraviolet (UV) laser ablation means. A high-quality laser ablation zone without visible resin residue and broken carbon fiber has been presented by one-pass laser ablation when a particular scarfing conditions combination was used. Meanwhile, a depth-controlled surface-forming approach was gained, accompanied by multiple laser scanning. Subsequently, a hybrid laser treatment strategy was provided for characteristic structure generation, and a novel stepwise structure was constructed for verification.

Quartz cleavage fracturing and subsequent recrystallization along the damage zone recording fast stress unloading

Strings of recrystallized grains along cleavage planes in host quartz crystals within pseudotachylyte-bearing breccias from the Silvretta basal thrust, Central European Alps, and within shocked gneisses from the Vredefort impact structure, South Africa, are compared and contrasted. The aim is to obtain the characteristic deformation and stress history during microfabric evolution. Strings of recrystallized grains occur in sets parallel to r- and z-rhombohedral planes of the host quartz in both localities and along basal planes in Vredefort gneisses. In Silvretta fault rocks, they exclusively occur in quartz clasts within tensional domains associated with the propagating pseudotachylyte-related fault tip, indicating that cleavage occurred simultaneously with pseudotachylyte generation. Cleavage of quartz in Vredefort gneisses is related to shock during impact. Quartz cleavage fracturing along planes of minimum free surface energy is suggested to require fast unloading from high transient stresses, as realized in both geological settings: unloading from >400 MPa within minutes during faulting and from <20 GPa within milliseconds during impact. An additional influence of thermal shock caused by frictional heating is likely. Strain-free grains grew in situ along the damage zone surrounding the cleavage fractures at quasi-isostatic stress conditions after deformation and temperatures to allow for static recrystallization of quartz.