Compressive Crack Research Articles

Experimental investigation on the mixture optimization and failure mechanism of cemented backfill with coal gangue and fly ash

Using coal gangue and fly ash for mining backfill materials can create a win-win situation for safe mining and waste disposal, with the critical challenge being the optimization of coal gangue grading and fly ash proportions. Uniaxial compression tests and scanning electron microscopy (SEM) observation were conducted on backfill specimens with different coal gangue grading and fly ash proportions, and in-situ monitoring of acoustic emission (AE) parameters and infrared radiation temperatures (IRT) was carried out. The elastic modulus, uniaxial compressive strength (UCS), failure pattern, infrared temperature, AE ringing count and energy evolution of the backfill were discussed. Further, the b-value and entropy-value of AE during the loading were analyzed. The results show that the UCS and elastic modulus decrease with the increase in the proportions of fly ash and large-size gangue. Tensile cracks generally dominate the failure of specimen under unaxial compressive load but shear cracks are more prone to occur for specimens with high proportions of fly ash and large-size gangue. The inner defects and weak interfaces between large-size gangue and cement pastes significantly affect the mechanical performance for specimens with high proportions of fly ash and large-size gangue. A sudden drop of the b-value occurs before the peak stress while the AE entropy-value reaches maximum at the peak stress. The methods and findings can guide the mixture optimization and mechanical failure analysis for backfill mining.

Axial compression behavior of prefabricated cruciform-section thin-concrete-encased steel short column

A novel prefabricated cruciform-section thin-concrete-encased steel (PCS-TCES) column is proposed. Tests were conducted on seven PCS-TCES short columns under axial compression, changing steel section area ratios, concrete cover thickness outside the flange, stirrup spacing and stirrup forms. According to the results, PCS-TCES short columns exhibit excellent axial compressive strength and crack resistance. The stirrup form with welded ends can further improve the crack resistance of the columns. The local buckling of steel sections under axial compression can be prevented by the thin concrete encasement of PCS-TCES columns. With the 45 mm concrete covers outside the flanges that is much thinner than the requirement in the Chinese code, the crack resistance and the deformability of the specimen are still enhanced. The proportion of steel section area in PCS-TCES short columns from 7.4% to 10.8%, although with thin concrete covers, can still fully utilize the strength of the steel and develop considerable residual resistance with satisfactory post-peak deformability. Formulas were proposed and verified to calculate the maximum axial compression resistance of PCS-TCES short columns, and a modification for the elastic stiffness formula in the Chinese code was provided.

An application of machine learning for material crack diagnosis using nonlinear ultrasonics

Crack diagnosis in non-destructive testing often requires reference data from the structure before damage or a considerable amount of response data. Also, detecting compression cracks is challenging. In this study, a machine learning-based method is proposed for diagnosing cracks in structures under compression. The method consists of convolutional neural networks (CNN) and fully connected networks (FCN). The CNN extracts features from nonlinear ultrasonic signal data, and the features determine the occurrence of fatigue cracks in a target specimen. Four types of input data are defined in accordance with the number of input frequency combinations. The performance of the proposed method is investigated using each data type to secure efficiency and accuracy in diagnosing aluminum specimens under various compression conditions. As a result, the F1 score, a measure of accuracy, of the proposed method depends on the number of input frequency combinations. The method detects high-compression cracks with high accuracy compared to the present technology specialized for compression cracks in a certain data type. A high accuracy of more than 96% is achieved with less computation time. The proposed method will provide an accurate crack diagnosis for compression cracks with reduced time and effort.

Experimental assessment on the dynamic mechanical characteristics and cracking mechanism of hybrid basalt-sisal fiber reinforced concrete

Hybrid basalt-sisal fiber reinforced concrete (BSFRC) has good application prospects in construction engineering, while the research on its mechanical properties and impact resistance is rather limited. In this study, to systematically investigate the dynamic compressive behavior and cracking characteristics of BSFRC, 9 kinds of concrete specimens containing different fibers and contents were prepared and a series of dynamic compression tests under strain rates of 45–150 s−1 were conducted via the split Hopkinson pressure bar (SHPB) apparatus. For the 9 typical types of concrete prepared in this study, the B1SP2 (i.e., concrete containing 0.1 vol% basalt fibers, 0.1 vol% sisal fibers and 0.1 vol% polypropylene fibers) shows the highest dynamic compressive strength, and the B2S2 (i.e., concrete containing 0.2 vol% basalt fibers and 0.2 vol% sisal fibers) exhibits the highest energy dissipation density. By means of high-speed photography, digital image correlation (DIC) and scanning electron microscope (SEM) techniques, the progressive failure process and microscopic fracture mechanism of BSFRC were further revealed. Fibers in BSFRC effectively inhibit the expansion and penetration of microcracks, and thus delay the initiation and coalescence of macrocracks. Similar to basalt fibers, sisal fibers control cracking behavior of concrete mainly by cutting crack propagation path and exerting bridging effect, and its fiber action is more remarkable for larger cracks. Furthermore, the coupling effect of strain rate and fiber action on the dynamic mechanical behavior of BSFRC were discussed. High loading rate activates more fibers to exert the strength-enhancement and crack-inhibition effect, and the fiber action makes the strain rate dependance of compressive strength more pronounced in BSFRC than that in plain concrete.

Improved high-temperature resistance of limestone calcined clay cement (LC3) paste with biochar: Multiscale evaluation and mechanistic analysis

In this research, the effects of biochar on the evolutions of the LC3's residual compressive strength, cracking, and ultrasonic pulse velocity were investigated after being heated to 300, 550, and 900 °C. The novelty of this study lies in the dual effect of adapting to climate change while optimizing high temperature resistance by encapsulating biochar in LC3. Moreover, an experimental design that applies multiple analytical methods and macro-micro mutual verification. The compositional changes in the hydration products and interface microstructure were analyzed in detail. The results showed that biochar increased the residual compressive strengths and curbed the crack's development. Especially at 900 °C, 1% and 2% of biochar increased its strength by 14.86% and 27.55%, respectively. These improvements may be closely related to the porous structure of biochar. The results of this study provide a valuable reference for the high temperature resistance of LC3 and help to deepen its understanding.

Progressive damage analysis of double-layer variable thickness 3D woven composite scaled engine casing

Due to the excellent mechanical properties and strong design flexibility, the 3D woven composite engine casing shows great potential in high performance fields. This article adopted the method of double-layer weaving and adding yarn to achieve the variable thickness of the 3D woven composite engine casing. The purpose of this article is to study the compression performance and failure mechanism of this variable thickness casing in different thickness zones through experiments and numerical simulations to lay a foundation for future optimization and inclusiveness research on this casing with complex thickness changes. Three types of representative volume cells are established for progressive damage analysis. 3D-Hashin criteria and von-Mises stress criterion are used as damage criteria for yarns and matrix. The progressive damage process and the proportion of damage in the inner and outer layers of three types of 3D woven tubes under axial compression load are analyzed. Results show that the main failure modes of the three types of tubes are yarn-matrix compressive cracking along direction 3 and matrix failure. The damages are mostly concentrated in the warp bending area. The proportions of warp yarn damage in the inner and outer layers of three tubes are different.

Near-in-situ investigation of surface crack healing and strengthening mechanism of Ti-43.5Al-4Nb-1Mo-0.1B alloy by novel electroshock treatment

The Ti-43.5Al-4Nb-1Mo-0.1B (TNM) alloy is prone to emerge surface cracks and other defects during processing and service, which will deteriorate the mechanical properties and fatigue life of the materials. In this work, a novel electroshock treatment (EST) for the surface crack repair and strengthening process has been proposed. Combined with near-in-situ experiments and theoretical analysis, the influence law and healing mechanism of different current densities and EST modes on the healing of surface cracks in the alloy were investigated. The scanning electron microscopy (SEM) near-in-situ observation reveals that the main factors influencing the healing of surface cracks relate to the time of energization, the current density, and the cracking angle. Meanwhile, the crack tip and locally bulging deflected positions are more likely to be healed in a short time under continuous EST mode and medium current density (75 A/mm2). The surface crack width at the calibration position decreases from 0.47 μm and 2.23 μm to 0 μm and 0.03 μm, respectively. The electron back scattered diffraction (EBSD) results show that the dislocation density increases around the surface crack healing area, and the dislocation density at the crack tip and away from the healing region is decreased and uniformly distributed after EST, which can further suppress the generation and propagation of the crack, resulting in a 20.1 % increase in tensile strength and a 40.3 % increase in fracture strain. Considering the coupling influence of the thermal and non-thermal effects of EST, a two-stage progressive atomic diffusion of thermal compressive stresses and crack bonding interfaces has been proposed to describe the evolution process of surface crack healing during EST.

Mechanical Characteristics and Damage Constitutive Model of Fiber-Reinforced Cement-Stabilized Soft Clay

Marine soft clays are prevalent in coastal regions of China, giving rise to engineering challenges such as salt swelling, corrosion, and load bearing in foundations with soft soil. This study is dedicated to enhancing the mechanical properties of fiber-reinforced cement-stabilized soft clay (FCSSC) and revealing its strengthening mechanism. Uniaxial compression tests are performed to explore the impact of fiber length, fiber amount, and curing ages on mechanical behavior. The stabilization mechanisms of cement and glass fibers are explored through damage analyses and microscopy. Based on the experimental results, a damage constitutive model is formulated for FCSSC, and its validity is established by comparing fitting curves with testing curves. The results demonstrate a significant improvement in the mechanical properties of the stabilized soil, attributed to the synergistic effects of the cement and glass fibers. The growth rate of the unconfined compressive strength decreased with increasing curing ages. Notably, the fiber length significantly impacted the strength index, with short-chopped fibers playing a crucial role in strength enhancement. The compressive strength exhibited an initial increase followed by a decrease with rising fiber content, reaching a maximum between 0.3% and 0.4%. The bridging effect of the glass fibers proved effective in inhibiting compression crack expansion and mitigating structural damage of the soil sample. However, excessive fiber content or length led to improved local porosity, resulting in the deterioration of strength and deformation properties. The stress–strain curves fitted using the proposed damage constitutive model accurately reflected the stress–strain relationship and deformation characteristics of the FCSSC.

Structural Performance Evaluation of Cross Dapped Connection for Vertical Wall to Wall Connection of Precast Wall Panel

In the context of Industrialised Building Systems (IBS), precast concrete buildings are composed of multiple structural members that are interconnected through different techniques. The adoption of precast concrete wall panels has gained significant traction in contemporary construction methodologies. Nevertheless, the utilization of dapped connections specifically designed for non-load bearing applications in precast walls incorporating recycled concrete aggregate (RCA) remains largely unexplored and limited in practice. This research proposes a new wall-to-wall connection for precast wall panels to enhance the constructability of IBS for non-load bearing walls. The novel Cross Dapped (CD) design enables horizontal panel installation in confined areas with existing structural frames, while ensuring the connection’s strength as a non-load bearing wall to prevent failure. Uniformly distributed loads are applied until sample failure, recording compressive load patterns, deflection, stress-strain patterns, and crack patterns on the wall surface. The CD connection demonstrates applicability for precast wall-towall connections, improving IBS constructability with its innovative design and locking system. Overall, this research explores and proposes an efficient and structurally sound wall-to-wall connection design for precast wall panels of non-load bearing system, facilitating the adoption of IBS methods, and improving the overall quality and constructability of building systems.

The Mechanism of Mineral Dissolution on the Development of Red-Bed Landslides in the Wudongde Reservoir Region

The Wudongde reservoir region exhibits a notable prevalence of landslides within the red-bed reservoir stratum. The red bed is a clastic sedimentary rock layer dominated by red continental deposits. It is mainly composed of sandstone, mudstone, and siltstone. The lithology is diverse and uneven. In this study, we delve into the impact of mineral dissolution on the development of red-bed landslides in the reservoir area by utilizing the Xiaochatou landslide as a representative case study. Considering the inherent susceptibility of red-bed formations to erosion, collapse, and softening when exposed to water, an investigation was conducted to examine the consequences of mineral dissolution on landslides occurring in these areas. We conducted a mineral analysis and an identification of rock samples from the Xiaochatou landslide site, revealing alternating layers of sandstone and mudstone. Sandstone and conglomerate specimens were immersed in deionized water, and advanced techniques such as scanning electron microscopy (SEM), ion chromatography (IC), and inductively coupled plasma (ICP) analysis were used to examine the effects of water immersion. We also employed the hydrogeochemical simulation software PHREEQC to understand the dissolution mechanism of gypsum during soaking. Our findings reveal that sandstone and conglomerates harbor a notable quantity of gypsum, which readily dissolves in water. Prolonged immersion leads to erosion cavities within the sandstone, thereby augmenting its permeability. The concentration of SO42− ions in the soaking solution emerges as the highest, followed by Ca2+ and Na+. The notable significance is the dissolution of gypsum, whose intricate mechanism is contingent upon diverse environmental conditions. Variations in ion concentration profoundly influence the saturation index (SI) value, with the pH value playing a crucial role in shifting the reaction equilibrium. Regarding the deformation mode of the landslide, it manifests as a combination of sliding compression and tension cracking. The fracture surface of the landslide assumes a step-like configuration. As the deformation progresses, the mudstone layer takes control over the sliding process, causing the sandstone to develop internal narrow-top and wide-bottom cracks, which propagate upward until the stability of the slope rock mass is compromised, resulting in its rupture. In this manuscript, we delve into the dissolution traits of red-bed soft rock in the Wudongde reservoir area, using a landslide case as a reference. We simulate this rock’s dissolution under environmental water influences, examining its interaction with diverse water types through rigorous experiments and simulations. This study’s importance lies in its potential to shed light on the crucial engineering characteristics of red-bed soft rock.

The effects of different nano materials on the strain and crack length sensing performance of smart concrete: Phenomenological models

Nineteen concrete mixtures with multi wall carbon nano tube (MWCNT), graphene, nano scale (waste of steel industry, iron oxide) and suspensions of nano sized iron, zinc, and a composite suspension of nano sized iron, silver, copper, zinc were designed with different volume percent. The electrical resistivity decreased 229%, 176%, 113%, 251% with additions of graphene, MWCNT, nano scale, composite suspension of nano-sized iron, silver, copper, zinc, respectively. The compressive strain sensitivity of the mixtures increased 244%, 211%, 311% with addition of graphene, MWCNT, nano zinc suspension, respectively. Tensile strain and crack length sensitivities of reference and graphene added mixtures which had the highest compressive strain sensitivity were determined. Strong linear relationships between compressive strain, tensile strain and crack length versus electrical resistance change were observed. Detailed phenomenological models were presented for relationship between the graphene amount, tensile strain and crack sensitivities.

Experimental Study On Mechanical Behaviour Of Human Hair Reinforced Concrete

Fibre-reinforced concrete offers a practical and cost-effective solution for addressing micro-cracks and similar structural weaknesses in concrete. Traditional concrete is inherently weak in tension, necessitating measures to enhance its performance in this regard. One unconventional yet promising option for reinforcement is human hair due to its impressive tensile strength. Human hair fibres (HF) are readily available, affordable, and do not degrade quickly, which can contribute to environmental concerns. This study aims to investigate the impact of incorporating human hair fibres into plain cement concrete, with a focus on enhancing compressive strength, tensile strength, flexural strength, and crack prevention while promoting economic and eco-friendly concrete practices.
 Prior to incorporating human hair fibres into the concrete mix, a meticulous cleaning process involving acetone is carried out. Experimental assessments were conducted on concrete beams, cubes, and cylinders, utilizing various proportions of human hair fibres (0%, 1%, 1.5%, and 2% by weight of cement). The findings reveal that the introduction of human hair fibres as reinforcement leads to a noteworthy enhancement in concrete performance. Specifically, with a 2% inclusion of human hair fibres, we observed a 3.29% upsurge in compressive strength, a 10.87% increase in tensile strength, and a 12.69% improvement in flexural strength in comparison to traditional concrete.

A robust tension-compression asymmetric phase-field fracture model for describing PBX cracking under complex stress states

ABSTRACT The crack behaviors under complex stress states are very important for the safety of polymer-bonded explosives (PBXs) under accidental stimulations, but their accurate description is a challenge. Due to the advances of tracking discontinuities and multi-fields coupling, the phase-field model for complex fracture phenomena is attracting significant interest recently. Conventional phase-field fracture models are tension-compression symmetric or based on volumetric-deviatoric strain energy split, and these conventional phase-field models may lead to unrealistic fracture patterns, which hinders its further application in PBX fracture simulations. In this work, we present an extended, tension-compression asymmetric phase-field fracture model for PBXs, which distinguishes the contributions of tensile and compressive stresses to damage driving energy, and couples the mechanism of mechanical degradation and energy-driving cracking diffusion. We implemented our improved phase-field fracture model into finite element calculations and compared the simulation results with the conventional tension-compression symmetric phase-field fracture model and volumetric-deviatoric strain energy split phase-field fracture model by simulating PBX specimens under static loadings. The results show that our model not only accurately depicts the tensile and compressive cracks, but also describes compression-assisted cracking while suppressing unrealistic damage nucleation caused by small amplitudes of local compressive stresses, making it a very efficient way of describing PBX cracking under complex stress states. This new model is both mathematically and physically concise, and convenient for numerical implementation. Moreover, the novel model can be naturally extended to simulate shock-induced dynamic and/or coupled fracture of PBXs because of its feasibilities for dynamic extension and multi-field coupling.

Study on the influence of crack depth on the safety of tunnel lining structure

In order to study the mechanism of the influence of crack depth on the bearing capacity and stability of tunnel lining structure, the calculation model of internal force of lining with cracks is established based on the theory of fracture mechanics, and the variation of stability coefficient of lining structure with Ⅰ-Ⅱ composite cracks is analyzed. With the increase of the crack depth of the vault, the bending moment of the vault gradually decreases, the stress intensity factor increases, and the stability factor f gradually decreases. The critical depth of tensile and compressive crack instability propagation is 54.38% and 74.01% of the lining thickness, respectively. The relationship between load and displacement, internal force and contact pressure, crack propagation depth and time, and strain variation of the secondary lining vault during the loading process of cracks at different depths are analyzed. It is found that cracks have a significant impact on the bearing capacity of the secondary lining, and the deeper the cracks, the lower the bearing capacity and stability. When the crack depth is large, the tensile stress peaks in a short time, and applying smaller loads can also cause the crack to expand. When the crack depth is 0.9d (d is the thickness of the secondary lining), the bearing capacity of the structure decreases by 72.57%. The research results can provide certain theoretical guidance for the prediction and prevention of lining crack propagation during tunnel operation.

Experimental evaluation of axial compression performance of precast panels from bamboo-reinforced concrete

This research aimed to determine the performance of bamboo-reinforced concrete precast panels (BRCPP) subjected to axial compressive loads, validated using numerical simulations. Axial compressive load capacity, crack, and failure patterns were investigated and compared with steel-reinforced concrete precast panels (SRCPP) as a control. Eight panels were made with details of four BRCPP and SRCPP, having dimensions of 1200 × 400 × 50 mm3 each. The four SRCPPs consisted of two panels, produced in laboratories and two manufactured by local companies. The variations in bamboo reinforcement spacing were 150 mm and 180 mm, while the gap between steels was 180 mm, and panels were tested under axial compressive load. The results showed that the axial compressive load capacity of BRCPP with a bamboo reinforcement size of 12 × 12 mm2 at a distance of 150 mm was sufficient to meet the specifications of SRCPP panels produced by the local industry. Based on experimental, theoretical, and numerical simulation analysis, the performance of BRCPP showed suitability, making it a considerable choice, specifically for precast panels. The special advantage of BRCPP encompassed eco-friendliness and sustainability.

Crack initiation stress of thermally damaged rock under uniaxial compression

Crack initiation stress (CI) is an important index of rock and the index of thermally damaged rock under uniaxial compression is examined in this study. Methods for determining CI are first reviewed, and the CI values of two thermally damaged rocks are then identified using several methods including crack volumetric strain (CVS) method, lateral strain response (LSR) method, and cumulative acoustic emission hit (CAEH) method. The results show that CI estimated from the CVS method and the CAEH method is comparable with each other. On the other hand, it is found that CI determined using the LSR method is generally lower than these determined by the other two methods. Because the lateral strain of a thermally damaged rock is small (sometimes positive in the initial stage), the LSR method is not applicable for determining CI of thermally damaged rocks. A modified LSR (MLSR) method, which excludes the initial collapse deformation stage, is proposed, and the new method truly reflects new crack initiation. By comparing the determined CI with other methods, it is found that the proposed MLSR method is capable of determining CI of thermally damaged rock. Variation of CI with the degree of thermal damage is also studied. It is found that CI generally decreases as the number in the cyclic treatment increases, while the difference between CI to uniaxial compressive strength (UCS) ratio and crack damage stress (CD) to UCS ratio decreases with increasing thermal damage in the rock. The results indicate that unstable cracking propagation is easy to occur as the thermal damage in the rock increases.

Investigation on residual bond strength and microstructure characteristics of fiber-reinforced geopolymer concrete at elevated temperature

Fiber-reinforced geopolymer concrete has been attracting attention and interest worldwide due to its sustainable properties. However, few studies have reported the pull-out behaviour of fiber-reinforced geopolymer concrete (GPC) at elevated temperatures. In order to bridge this knowledge gap, a series of detailed investigations aimed to investigate the effect of elevated temperatures on the mechanical and microstructure properties of fiber-reinforced geopolymer concrete. In the present investigation, crimped steel fibers (SF), polypropylene fibers (PF), basalt (BF), and hybrid fibers such as SF:PF and PF:BF is employed to develop the GPC. Alkaline activators such as sodium hydroxide (NaOH) of 8 M and 10 M and Na2SiO3/NaOH ratios of 2.5 are used in the production of M35 and M40 grade GPC. Compressive strength, weight loss, crack pattern, bond strength, and microstructure of fiber-reinforced GPC specimens have been evaluated, after exposing to higher temperature following ISO 834 standard fire curve. Results from the conducted tests show that adding various types of fibers improves the compressive strength and bond strength of the GPC specimens. More specifically, amongst all tested specimens, the exposed GPC-BF shows lesser weight loss and higher residual compressive strength with fewer cracks on the surface of the specimens. on the other hand, GPC with SF shows higher residual bond strength than other fiber-reinforced GPC specimens. Microstructure analysis (SEM/EDAX) confirms the extent of damage and contribution of fiber in the temperature-exposed GPC. A statistical relationship and correlation has been obtained between compressive and bond strength.

Assessing the Impact of PVC Pipe Diameter on Compressive Strength and Cracking in Hollow Prism Concrete

In order to enhance the utilization of concrete, it is necessary to explore the impact of PVC pipes incorporated into hollow prism concrete, focusing on their effects on compressive strength and cracking. PVC pipes are commonly employed as reinforcements within concrete structures to bolster their stability. This research delves into the consequences of varying pipe diameters and PVC pipes within hollow prism concrete. The experimental process entails utilizing concrete prisms with 100 x 100 x 300 mm³ dimensions, possessing a compressive strength of 25 MPa. Research outcomes reveal that pipe diameter directly influences compressive strength, where larger diameters are associated with reduced compressive strength. Including pipes in the concrete does not yield a substantial discrepancy in compressive strength. Concrete prisms with incorporated pipes exhibit a Columnar-type collapse, indicative of dominant compressive stress, whereas prisms without pipes undergo a Shear-type collapse, signifying a shift in stress distribution. It emphasizes the pivotal role of reinforcements like PVC pipes in upholding the structural integrity of concrete, thereby mitigating potential damage.In order to enhance the utilization of concrete, it is necessary to explore the impact of PVC pipes incorporated into hollow prism concrete, focusing on their effects on compressive strength and cracking. PVC pipes are commonly employed as reinforcements within concrete structures to bolster their stability. This research delves into the consequences of varying pipe diameters and PVC pipes within hollow prism concrete. The experimental process entails utilizing concrete prisms with 100 x 100 x 300 mm³ dimensions, possessing a compressive strength of 25 MPa. Research outcomes reveal that pipe diameter directly influences compressive strength, where larger diameters are associated with reduced compressive strength. Including pipes in the concrete does not yield a substantial discrepancy in compressive strength. Concrete prisms with incorporated pipes exhibit a Columnar-type collapse, indicative of dominant compressive stress, whereas prisms without pipes undergo a Shear-type collapse, signifying a shift in stress distribution. It emphasizes the pivotal role of reinforcements like PVC pipes in upholding the structural integrity of concrete, thereby mitigating potential damage.

Structural behaviour of concrete structure under the axial load with respect to rust formation computed at the AI-support

The present study concerns the finite element modelling of structural behaviour for concrete structure subjected to the axial load and simultaneously corrosion of steel embedment. The structural capacity was expressed into the risk of cracking with respect to the compressive and tensile stress, while a development of steel corrosion was reflected by the increasing rust formation on the steel surface. To consider the buffering capacity at the steel–concrete interface against stress generated by the rust formation, the interfacial gap was taken, of which the width accounted for 10 µm. As a result, it was found that the tensile deformation could occur with only the axial load, which can be further developed by the rust formation. Also, the compressive deformation took place at the steel–concrete interface, arising from the steel corrosion, which had been marginally affected by the axial load. At the steel–concrete interface, the risk of cracking was strongly dependent on the position, due to the offset-effect of stress. Moreover, the compressive strength of concrete had a crucial impact on the risk of cracking, in particular, the compressive cracking could be adversely mitigated by the lower strength of concrete.

Effects of hydrogen on the dynamic mechanical properties and microstructure of 7055 and 7A52 aluminum alloys

In the present work, the effect of hydrogen on the impact resistance of the 7055 and 7A52 aluminum alloys have been experimentally investigated by using split Hopkinson pressure bar (SHPB) and electrochemical hydrogen charging technique. It was first found that hydrogen induced stress chase after yield deformation in 7055 and 7A52 alloys. Meanwhile, hydrogen reduced the yield strengths of the two alloys. Besides, the evolution of microstructures including cracks, particles and dislocations has been quantitatively analyzed by polarizing microscope (PM), scanning electron microscope (SEM) and transmission electron microscopy (TEM). It has been found that both two aluminum alloys are sensitive to hydrogen embrittlement under high-speed deformation conditions. The hydrogen causes hydrogen compression cracks at grain boundaries, pores, and Al2Cu particles in the material, and the hydrogen cracking of both aluminum alloys after impact appeared to be layered, and the lower layer cracking was flat, which indicated that the hydrogen made the alloy embrittle to some extent. Besides, hydrogen reduces the hindering effect of copper-containing phase and large η phase on dislocation movement, which makes the dislocations distribution inside the 7055 alloy grains more uniform. The results show that 7000-series aluminum alloys are sensitive to hydrogen embrittlement under high-speed deformation conditions.