Damaged Specimens Research Articles

Local buckling behavior and reinforced mechanisms of short circular timber columns confined with bamboo scrimber

Developing sustainable high-performance bamboo scrimber (BS) as structural and reinforcing materials is significant. BS was used as reinforcing material to increase ancient timber columns' load-bearing capacity and safety via a damage-free strengthening method. The BS panels were fastened to the surface of the wooden columns by spaced steel strips. The spacing of the steel strips was the important factor in balancing the appearance of the confined reinforced timber columns with maximizing the strength of the confined panels. In this study, eight short circular wooden columns reinforced with BS with varying spacing of steel strips were fabricated and tested under axial compression. Each specimen's damage characteristics, load-carrying capacity performance, and strain coordination were analyzed and compared. The reinforcement method has a significant effect, and the reinforcement system of all specimens provides an additional load-bearing capacity of more than 48.3 % with about 38 % increase in cross-section area. The load-bearing capacity decreases significantly with increasing the spacing of steel strips. When the steel strips' distance is more than 363 mm (the corresponding slenderness ratio is 41), the confined panel showed significant buckling behavior from the beginning of loading. In contrast, the confined panels of the other circular reinforced timber column showed buckling and load drop only near the peak load, which takes full advantage of the strength of the BS material. The strain growth trends of the confined panels and core column were similar, although the strain of the confined panels' bending offsets some of the compressive strain, which was evidence that they were synergistically stressed under axial compression. The part of confined slats between the steel strips was intercepted as a compression bar, and the commonly used equation for the load-bearing capacity of a flexible bar was introduced. Various flex rod equations based on material properties were calculated and compared to the test results. The calculations showed that the buckling equation suggested by Euler and CSA086-19 had the best agreement with BS materials with similar proportional limits and ultimate strength. BS as a flex rod was suggested with a slenderness ratio not exceeding 32, and a general equation for calculating the steel strip spacing considering the material thickness was proposed for construction reference.

Spatial rotational behaviour of intact and damaged column foot joints: numerical modelling

Columns in traditional Chinese timber structures barely rest on stone bases, and the column foot joints are capable of resisting moment around any direction. This study numerically investigated the spatial rotational behaviour of intact and damaged columns based on experiments. Unidirectional cyclic loading tests were carried out on two intact and three damaged column foot joint specimens. A fibre element-based numerical model for the column foot joints was developed and validated by use of the unidirectional loading test results. Numerical analyses were performed based on the fibre element-based model to obtain the rotational behaviour of the intact and damaged column foot joints under spatial loading. The analyses indicated that the moment–rotation curve of an intact column foot joint under spatial loading was on an umbrella-shaped surface. The damage at the column foot not only unidirectionally decreased the moment-resisting capacity of a column foot joint but also resulted in a rotational performance degradation valley on the moment–rotation surface of the joint. The rotational behaviour of both the intact and damaged column foot joints under spatial loading was highly non-linear. This developed fibre element-based model can be further utilised to analyse the structural performance of traditional timber structures under three-dimensional excitations.

Influence of fatigue damage on the impact performance of toughened-interleave carbon fibre epoxy composite laminates

The impact performance of mechanically fatigued carbon fibre-reinforced polymer (CFRP) composite laminates with and without thermoplastic toughening particles has been investigated through a joint experimental and numerical campaign. Prismatic carbon fibre/epoxy specimens with added toughening particles at the ply interfaces were mechanically fatigued with different load amplitudes leading to a loss in apparent stiffness of 10% to 15%. Following the fatigue loading, high resolution computed tomography (CT) has been performed, revealing varying degrees of delamination starting from the free edges along the length of the specimens. In addition, transverse matrix cracks are observed in all fatigued specimens regardless of the amount of delamination. The residual ballistic impact performance of the damaged specimens has been investigated in a dynamic three-point bending configuration at three different velocities, showing a significant detrimental effect of even barely visible initial delamination. In addition, post-mortem CT scans and detailed finite element simulations are used to gain further insight into the mechanisms by which the two types of initial damage affected the impact resistance of the laminates. Finally, repeating the same experiments on a similar CFRP system without discrete toughening particles showed that their inclusion significantly increased the impact resistance both with and without prior fatigue damage.

Experimental investigation on shear behavior of cracked reinforced concrete beams strengthened with carbon textile reinforced concrete

This study examines the strengthening effects of carbon textile-reinforced concrete (CTRC) on the shear behavior of pre-cracked reinforced concrete beams. Six reinforced concrete beams, each with an aspect ratio of 1.6, underwent three-point bending tests, comprising two control specimens and four strengthened specimens. Prior to the application of U-wrapped carbon textile reinforcement, all beams were subjected to pre-loading to induce shear cracking. The strengthening process involved utilizing either two or three layers of carbon textile. The findings reveal a significant enhancement in the shear capacity of the CTRC-strengthened beams compared to the control beams. Notably, the shear strength of the specimens reinforced with two layers of carbon textile increased by 34.7%, whereas those reinforced with three layers increased by 50.9% compared to the control specimens. Thus, carbon TRC effectively restored and elevated the shear capacity of damaged specimens to levels akin to those of control beams.

Experimental investigation on shear behavior of cracked reinforced concrete beams strengthened with carbon textile reinforced concrete

This study examines the strengthening effects of carbon textile-reinforced concrete (CTRC) on the shear behavior of pre-cracked reinforced concrete beams. Six reinforced concrete beams, each with an aspect ratio of 1.6, underwent three-point bending tests, comprising two control specimens and four strengthened specimens. Prior to the application of U-wrapped carbon textile reinforcement, all beams were subjected to pre-loading to induce shear cracking. The strengthening process involved utilizing either two or three layers of carbon textile. The findings reveal a significant enhancement in the shear capacity of the CTRC-strengthened beams compared to the control beams. Notably, the shear strength of the specimens reinforced with two layers of carbon textile increased by 34.7%, whereas those reinforced with three layers increased by 50.9% compared to the control specimens. Thus, carbon TRC effectively restored and elevated the shear capacity of damaged specimens to levels akin to those of control beams.

The problem of taxonomic uncertainty in biosecurity: South African mite interceptions as an example

International trade continues increase, with agricultural trade being a major pathway for transport and introduction of pests to new regions. We use South Africa’s interception records to highlight particular challenges related to mites detected on agricultural plants and fresh produce. These challenges include interception of damaged or immature specimens, lack of local and global taxonomic specialists, uncertainties in understudied taxa, lack of availability or access to reference material, and difficulties with international collaborations. As an example, we present a particularly notable case of a Brevipalpus interception which took sixteen years to positively identify. This mite was intercepted 54 times (2007-2023) on European kiwifruit imported to South Africa. The first interceptions were from Italy in 2007, then in 2010 from Greece, and in 2015 from France. Despite repeated interceptions, various challenges hampered our ability to identify the species, until in 2023 it was eventually identified as Brevipalpus garmani Baker. We discuss the implications of this and other interceptions for biosecurity in agricultural trade.

Study on flexural behavior of concrete slabs strengthened with externally prestressed recycled bead wires

Recycled bead wires were prestressed for reinforced concrete slabs using an innovative anchor that our research group created. In this work, four concrete slab groups were designed: three reinforced groups and one control group. In this work, four concrete slab groups: three reinforced groups, and one control group were designed. The reinforced slabs were subjected to controlled stretching stress of 720 MPa, 900 MPa, and 1080 MPa. Four-point bending static load experiments were performed to verify the recommended reinforcement method and assess the effect of different controlled stretching stress on slab bending performance. This paper presents an analysis of the bearing capacity, crack behaviour, stiffness, and ductility of the specimens. The superior tensile and flexural capabilities of recycled bead wires were used as external prestressing reinforcement materials, as evidenced by the results. The reinforced slab exhibited a maximum increase in ultimate bearing capacity of 142 %, resulting in a significant enhancement of its flexural bearing capacity. The overall stiffness of the slab was successfully increased using recycled bead wires, and the fractures of the reinforced slab exhibited characteristics of fine and dense material. The 'inverted arch' effect of prestressed steel wires efficiently controlled the breadth of the fracture, postponed the onset of cracks, and decreased the degree of specimen damage. The application of more controlled stretching stress was associated with higher carrying capacity, and this also better restricted the development and expansion of cracks. A numerical simulation of four sets of concrete slabs was conducted using ABAQUS, with a subsequent comparative analysis of the results obtained with those of the experimental tests. Furthermore, the feasibility of this type of reinforcement was also confirmed by theoretical analyses of ultimate load-carrying capacity and cracking deflection. Their low-carbon qualities can address issues with waste resources and create new concepts for recycled waste tires.

LIQUID PERMEABILITY OF EUCALYPTUS UROPHYLLA WOOD TREATED WITH DIFFERENT DRYING METHODS

In this study, the influence of three different drying methods on the liquid permeability of sapwood and heartwood of Eucalyptus urophylla was investigated. The liquid permeability of the dried wood was assessed by measuring the maximum amount of dyeing solution uptake using the capillary rise method. Subsequently, the microscopic structure of the dried wood was examined by scanning electron microscopy (SEM). The results indicated that the liquid permeability of sapwood dried by microwave vacuum drying (MVD) and conventional kiln drying (KD) was significantly more effective than that of air drying (AD) treated wood. However, there is no significant difference in the effect of MVD and KD on the liquid permeability of sapwood. The liquid permeability of heartwood treated with MVD is significantly better than that treated with KD and AD, and the effect in the effects of AD and KD on the heartwood is not significant. The increased permeability of Eucalyptus urophylla wood can be attributed to the occurrence of macro-cracking or micro-structural damage in the test specimens, resulting from the dislodgement of perforated plates within the wood cells, the rupture of the intercellular layer between vessel and axial parenchyma cells, as well as the rupture of the pit membrane in cross-field pits due to microwave vacuum drying and conventional kiln drying.

Low-velocity impact response optimization of the foam-cored sandwich panels with CFRP skins for electric aircraft fuselage skin application

Abstract Composite sandwich structures are widely used in the aerospace field due to their advantages of high strength, lightweight, and fatigue resistance. However, these structures are prone to damage with very-low-energy impacts. In order to improve the impact resistance of aircraft skin structure, a low-velocity impact resistance of sandwich structure specimens was tested by means of drop hammer impact, and the impact damage area was scanned by ultrasonic C-scan, and obtains the impact damage of specimens with different impact energies and different ply sequences. Combined with the Hashin failure criterion, the finite element equivalent model of composite sandwich structure under low-velocity impact was established. The errors between the simulation results and the C-scan results of the test piece were less than 10%, in which the experimental measurements and numerical predictions were in close agreement. Finally, the finite element equivalent model was applied to optimize the application of model sandwich, which was used for fuselage skin of a certain electric aircraft. The total thickness of the laminate structure remains unchanged before and after optimization, but the impact resistance was significantly enhanced. The ±45° lay-up was beneficial for the structure to absorb the impact energy.

Examination of the stress-strain model for confined concrete considering the impact of corroded spiral bars

To examine the impact of corroded spiral bars on the confinement effect of concrete, a series of dry-wet cyclic accelerated corrosion tests and axial compression tests were performed on 36 RC (Reinforced Concrete) specimens. This study investigated the effects of various factors, including the degree of corrosion in spiral bars, the reinforcement configuration, and the concrete strength grade, on the axial compressive performance of confined concrete. The mechanical behavior of concrete, which was confined by corroded spiral bars, was analyzed by considering the corrosion characteristics, failure patterns, and load-carrying capacity of the specimens. A modified Mander model, which incorporates the influence of corroded spiral bars, was developed. The results indicate that increased corrosion accelerates specimen damage and reduces ductility. Stirrups show pull-off phenomena. A higher stirrup ratio enhances the bearing capacity and deformation capacity of specimen during destruction, while reducing longitudinal reinforcement buckling. Stronger concrete delays vertical cracking, increases bearing capacity, but reduces deformation capacity during destruction. The modified Mander model demonstrates high computational accuracy.

Study on Mechanical and Acoustic Emission Characteristics of Backfill-Rock Instability under Different Stress Conditions.

Unveiling the mechanical properties and damage mechanism of the complex composite structure, comprising backfill and surrounding rock, is crucial for ensuring the safe development of the downward-approach backfill mining method. This work conducts biaxial compression tests on backfill-rock under various loading conditions. The damage process is analyzed using DIC and acoustic emission (AE) techniques, while the distribution of AE events at different loading stages is explored. Additionally, the dominant failure forms of specimens are studied through multifractal analysis. The damage evolution law of backfill-rock combinations is elucidated. The results indicate that DIC and AE provide consistent descriptions of specimen damage, and the damage evolution of backfill-rock composite specimens varies notably under different loading conditions, offering valuable insights for engineering site safety protection.

Bending behavior and damage evolution of GLARE laminate using in‐situ AE technology and FEM

AbstractGLARE laminate experiences multiple damage modes during bending failure, including fiber fracture, matrix cracking, interlayer delamination, and fracture of aluminum alloy. In most cases, two or more failure modes occur together, which makes the damage process complex and unpredictable. This paper proposes a combination of experimental testing and numerical simulation to investigate the influence of fiber lay‐up direction and center open‐hole on the bending failure behavior of GLARE laminate. Simultaneously, Acoustic Emission (AE) technology was used to monitor the bending process of GLARE laminates in real‐time, and a numerical simulation model for the three‐point bending of GLARE laminates was established. The experimental results showed that the bending strength of intact specimens decreased significantly with the increase of the fiber off‐axis angle, whereas the strength retention of open‐hole specimens increased significantly with the increase of the fiber off‐axis angle. Based on the K‐means++ clustering algorithm, the peak frequencies corresponding to different damage modes of GLARE laminates were identified as follows: aluminum alloy damage [1–70 kHz], matrix cracking [93–210 kHz], interlaminar delamination [211–304 kHz], and fiber breakage [304–516 kHz]. The simulation results agreed well with the experimental results, showing that the damage in intact specimens initiated at the laminate edges and propagated sequentially along the thickness direction, while the damage in open‐hole specimens initiated at the hole edges and then propagated towards the laminate edges.Highlights The present study investigated the effects of fiber lay‐up direction and central open‐hole on the bending performance and failure behavior of GLARE laminate. In‐situ monitoring of the GLARE laminate during three‐point bending was conducted using AE technology. A model for simulating the progressive damage of GLARE laminate was established and its accuracy was verified.

Seismic performance evaluation of prefabricated concrete shear walls with anchorage defects

In this study, the effects of grouting sleeve anchorage defects on the seismic performance of prefabricated concrete shear walls were studied, and a fast after-damage retrofitting method has been proposed. Six specimens were investigated under cyclic loading. The parameter was the number of grouting sleeve anchorage defects, selected as 0, 2, and 4. The test was divided into two loading stages. During stage 1, the specimen was loaded until the strength dropped below 85 % of its peak strength. After stage 1, the damaged specimens were retrofitted using combined retrofitting method of steel plate and high-strength grouting material, and then subjected to loading tests in stage 2. The resulting damage characteristics, hysteretic behavior, stiffness, strength, and energy dissipation capacity were studied. The strength of the shear wall, considering anchorage defects, was calculated. The results show that anchorage defects reduce the seismic behavior of the specimens. Compared with the two defects, the strength of the shear wall with four defects did not significantly change, though the ductility coefficient and energy dissipation capacity decreased considerably. The combined steel plate-high strength grout retrofitting method could significantly improve the strength and energy dissipation and effectively restore the stiffness of prefabricated shear walls. The calculated strength of the shear wall is in good agreement with the experimental value, confirming that it is reliable and can be used to calculate the strength with anchorage defects. The proposed retrofitting method can provide a new choice for the fast damage repair of the post-earthquake shear walls.

Experimental study on the bearing mechanical characteristics and deformation failure mechanism of damaged sandy mudstone

AbstractStudying the mechanical properties and failure mechanisms of damaged rocks holds practical significance in guiding tunnel or roadway support and assessing the stability of engineering rock masses. To uncover the failure mechanisms of sandy mudstone with varying degrees of damage, we conducted cyclic loading‐unloading tests to create specimens at different damage levels. Subsequently, uniaxial loading tests were performed to investigate the fundamental mechanical properties, wave velocity, and acoustic emission (AE) parameter evolution characteristics of the damaged specimens. The classification of damaged rocks was based on the energy evolution characteristics of damaged sandy mudstone. Finally, we discuss the damage and deterioration mechanisms of different types of sandy mudstone. The findings contribute to establishing a theoretical foundation for evaluating the degree of rock damage.

Study on multi-scale dynamic mechanical properties of metakaolin modified recycled aggregate concrete under coupling conditions of sulfate attack and dry-wet cycles

To explore the potential of modified recycled aggregate concrete for use in construction projects, the evolution of its properties in the combined effects of environment and loading was investigated. This paper considered various factors, including the replacement amount of metakaolin (0 %, 15 %), dry-wet cycles (0, 20, 60, and 120 cycles), and the dynamic strain rate (ε˙ = 10−5/s, 10−4/s, 10−3/s, and 10−2/s), and conducted uniaxial compression, scanning electron microscopy (SEM), and X-ray diffraction (XRD) tests. The experimental findings demonstrated that the peak stress and elastic modulus of recycled aggregate concrete (RAC) exhibited a pattern of initial increase followed by a decrease before and after 20 dry-wet cycles, a concurrent upward trend was observed in both parameters with an escalation in strain rate and the incorporation of metakaolin (MK), and no uniform trend was observed for the peak strain. The test results from SEM and XRD revealed that the persistent formation of sulfate crystals and expansive substances like gypsum and ettringite were the primary factors contributing to the deterioration of specimen damage as cycle counts escalated. A quantitative analysis was conducted to investigate the mesoscopic damage mechanism associated with the dynamic mechanical properties and durability evolution process of metakaolin-based RAC under sulfate erosion. The correlation between the macroscopic mechanical properties and the microscopic changes of RAC was explored using statistical damage theory.

Minimally destructive hDNA extraction method for retrospective genetics of pinned historical Lepidoptera specimens

The millions of specimens stored in entomological collections provide a unique opportunity to study historical insect diversity. Current technologies allow to sequence entire genomes of historical specimens and estimate past genetic diversity of present-day endangered species, advancing our understanding of anthropogenic impact on genetic diversity and enabling the implementation of conservation strategies. A limiting challenge is the extraction of historical DNA (hDNA) of adequate quality for sequencing platforms. We tested four hDNA extraction protocols on five body parts of pinned false heath fritillary butterflies, Melitaea diamina, aiming to minimise specimen damage, preserve their scientific value to the collections, and maximise DNA quality and yield for whole-genome re-sequencing. We developed a very effective approach that successfully recovers hDNA appropriate for short-read sequencing from a single leg of pinned specimens using silica-based DNA extraction columns and an extraction buffer that includes SDS, Tris, Proteinase K, EDTA, NaCl, PTB, and DTT. We observed substantial variation in the ratio of nuclear to mitochondrial DNA in extractions from different tissues, indicating that optimal tissue choice depends on project aims and anticipated downstream analyses. We found that sufficient DNA for whole genome re-sequencing can reliably be extracted from a single leg, opening the possibility to monitor changes in genetic diversity maintaining the scientific value of specimens while supporting current and future conservation strategies.

Analysis of the influence of damp-heat aging on the shear failure of the adhesive joint of composite materials

Abstract In this study, a comprehensive temperature and humidity environment chamber was used to accelerate the artificial aging of carbon fiber bonded joint specimens in wet and hot environments, and shear tests were conducted on non-aging and wet and hot aging specimens, respectively. At the same time, acoustic emission technology was used to monitor the damage to the specimen, and the influence of wet and heat aging on the shear properties and damage forms of the bonded joint was explored. It is found that under shearing load, the unaged bonded joint specimens first show delamination degumming damage with an energy distribution of about 1000 (mV*mS) and then fiber fracture damage with an energy distribution of more than 4000 (mV*mS). According to the load strain curve, it can be seen that the shear strength of the moisture-heat aging specimen decreases by 30% compared with that of the non-aging specimen, from 33.6 kN to 22.3 kN. According to the load energy curve, it can be seen that the rubber layer of the specimen is damaged at the inflection point of the load curve, the rubber layer of the non-aging specimen is damaged at 15 kN, and the rubber layer of the moisture-heat aging specimen is damaged at 8 kN. The test results show that the wet heat aging reduces the interlayer properties of the specimens. The structural adhesive delamination is serious, which leads to the damage of the aged specimens in advance compared with the non-aged specimens. The overall deformation of the specimens increases.

Damping monitoring methods during ultrasonic fatigue testing: A comparative study.

Ultrasonic fatigue testing is quite a useful tool for exploring the high-cycle and very-high-cycle fatigue properties of materials. Damping monitoring has been proved to be fairly effective in indicating the generated defects or damage in the testing specimen. In this work, two damping monitoring methods are comparatively studied, i.e., our recently proposed quantitative electromechanical impedance method and the traditional vibration-free decay method. Industrial pure copper and 6061 aluminum alloy are used for fatigue testing and damping monitoring. To exclude the differences of temperature effect on the testing system, the same duty ratio of 15.4% is employed in the ultrasonic fatigue testing. The results show that both methods can effectively monitor the system damping during testing and the damping evolution process just before failure. Specifically, the free decay method can obtain more damping data and has advantages in monitoring metals, such as aluminum alloys, whose fracture process is very quick. However, the system damping obtained by free decay is strongly dependent on the testing stresses and signal processing and is thus not suitable for failure prediction of specimens. In comparison, the system damping obtained by using the quantitative electromechanical impedance method is independent of the testing stresses. Thus, a definite relationship between the system damping and specimen's internal friction can be established. However, tens of seconds are required for accurate damping measurement using the quantitative electromechanical impedance method, leading to a low duty ratio of the ultrasonic fatigue testing. In practical, both the methods are suggested for monitoring of early damage during ultrasonic fatigue testing.

Durability Analysis of Cold Spray Repairs: Phase I-Effect of Surface Grit Blasting.

This paper presents the results of an extensive investigation into the durability of cold spray repairs to corrosion damage in AA7075-T7351 aluminium alloy specimens where, prior to powder deposition, the surface preparation involved grit blasting. In this context, it is shown that the growth of small naturally occurring cracks in cold spray repairs to simulated corrosion damage can be accurately computed using the Hartman-Schijve crack growth equation in a fashion that is consistent with the requirements delineated in USAF Structures Bulletin EZ-SB-19-01, MIL-STD-1530D, and the US Joint Services Structural Guidelines JSSG2006. The relatively large variation in the da/dN versus ΔK curves associated with low values of da/dN highlights the fact that, before any durability assessment of a cold spray repair to an operational airframe is attempted, it is first necessary to perform a sufficient number of tests so that the worst-case small crack growth curve needed to perform the mandated airworthiness certification analysis can be determined.

Development and characterization of phospho-ubiquitin antibodies to monitor PINK1-PRKN signaling in cells and tissue

ABSTRACT The selective removal of dysfunctional mitochondria, a process termed mitophagy, is critical for cellular health and impairments have been linked to aging, Parkinson disease, and other neurodegenerative conditions. A central mitophagy pathway is orchestrated by the ubiquitin (Ub) kinase PINK1 together with the E3 Ub ligase PRKN/Parkin. The decoration of damaged mitochondrial domains with phosphorylated Ub (p-S65-Ub) mediates their elimination though the autophagy system. As such p-S65-Ub has emerged as a highly specific and quantitative marker of mitochondrial damage with significant disease relevance. Existing p-S65-Ub antibodies have been successfully employed as research tools in a range of applications including western blot, immunocytochemistry, immunohistochemistry, and enzyme-linked immunosorbent assay. However, physiological levels of p-S65-Ub in the absence of exogenous stress are very low, therefore difficult to detect and require reliable and ultrasensitive methods. Here we generated and characterized a collection of novel recombinant, rabbit monoclonal p-S65-Ub antibodies with high specificity and affinity in certain applications that allow the field to better understand the molecular mechanisms and disease relevance of PINK1-PRKN signaling. These antibodies may also serve as novel diagnostic or prognostic tools to monitor mitochondrial damage in various clinical and pathological specimens. Abbreviations: AD: Alzheimer disease; CCCP: carbonyl cyanide 3-chlorophenylhydrazone; ELISA: enzyme-linked immunosorbent assay; HEK293E cell: human embryonic kidney E cell; ICC: immunocytochemistry; IHC: immunohistochemistry: KO: knockout; LoB: limit of blank; LoD: limit of detection; LoQ: limit of quantification; MEF: mouse embryonic fibroblast; MSD: Meso Scale Discovery; n.s.: non-significant; nonTg: non-transgenic; PBMC: peripheral blood mononuclear cell; PD: Parkinson disease; p-S65-PRKN: phosphorylated PRKN at serine 65; p-S65-Ub: phosphorylated Ub at serine 65; Ub: ubiquitin; WT: wild-type.