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Paper‐based friction materials with phenolic resin as the matrix are prone to thermal damage under harsh working conditions easily leading to materials failure. To satisfy the requirements of high speed and heavy load service situations, paper‐based friction materials with different polyimide resin content were prepared by wet forming technology to reveal the effect of polyimide resin on the properties of composites. And a paper‐based composite with phenolic resin was used for comparison. Results show that compared with the phenolic composite, tensile strength, and shear strength of the polyimide composite were increased by 50.5% and 36.4%, respectively. Due to the strong hydrogen bond in the imide ring of polyimide, the temperature of the polyimide composite at 2% weight loss was 292.7°C, which was 106.3°C higher than that of the phenolic composite. Moreover, the wear rate was reduced by 30.3% because the friction transfer film was produced during friction. To sum up, polyimide resin has the potential to replace phenolic resin under the condition of high speed and heavy load. Besides, the composite with polyimide resin content of 40.0 wt% demonstrated the best wear resistance and considerable strength attributed to the best interface combination. This research lays a theoretical foundation for the application of polyimide resin to paper‐based friction materials. [ABSTRACT FROM AUTHOR]

Using the example of assessing the technical condition of the trunnions of drying cylinders in cardboard machines (CBM), the question of the possibility of ranking cyclically loaded elements of dynamic equipment according to the degree of damage to their material by fatigue cracks using acoustic emission (AE) measurements is discussed. As a result of special laboratory studies with varying loads in the cycle of loading and lubrication of crack edges, the features of AE due to the friction of crack edges and plastic deformation at the crack tip during its growth in a viscous material have been established. It is shown that during cyclic loading of the material, AE signals from the friction of its banks are detected more steadily than AE signals due to a crack jump with an increase in its length, and that tracking the former ensures the detection of fatigue damage in the material even under loading conditions insufficient for crack growth. Based on the data obtained, three AE signs of the presence of fatigue damage in the material of the elements of dynamic equipment were developed under the condition of cyclic activation of the movement of crack edges. As a result of industrial testing of the developed AE signs, their operability was confirmed, their boundary values on the operating trunnions of CBM drying cylinders were clarified, and a method for ranking trunnions by the level of damage due to fatigue cracks was proposed. By comparing the results of AE measurements with ultrasound testing, the reliability of the proposed approach was evaluated and showed the probability of detecting a fatigue crack in the trunnions of CBM drying cylinders at the level of 71%, with the probability of skipping and false rejection of the product of 12 and 17%, respectively. The developed technique is also transferable to other massive dynamic equipment after clarifying the boundary values of AE signs of fatigue damage in the material on this type of facilities. [ABSTRACT FROM AUTHOR]

This paper reports on a special pilot coating and industrial printing trial designed to gain fundamental knowledge on ink adhesion failure on coated papers. We found that ink adhesion failure resulted in white spots without ink on the paper, referred to as uncovered areas and these spots gave print mottle problems. The white spots were due to two fundamentally different types of ink adhesion failure. One is the well-known ink rejection, which simply means that ink is not transferred to the surface. The other is a new type of ink adhesion failure, confirming a previous hypothesis suggested from laboratory observations. We refer to this as ink-lift-off adhesion failure, meaning that ink initially deposited on the paper surface becomes lifted off from the surface in a subsequent print unit. Adhesion failure by this mechanism was seen to occur more frequently than failure due to the well-known ink rejection. [ABSTRACT FROM AUTHOR]

Measured local paper structure—i.e. local basis weight, local thickness, local density and local fiber orientation—has been linked to local strain and local material failure (local temperature increase due to energy dissipation upon fiber–fiber bond failure) measured during tensile testing. The data has been spatially linked through data map registration delivering several thousand 1 × 1 mm 2 paper regions, each containing all measured properties. The relation between local paper structure and resulting local deformation and failure is studied with regression models. Multiple linear regression modeling was used to identify the paper structure related drivers for local concentrations of strain under load and local concentrations of material failure, which are both starting to occur considerably before rupture of the paper. Analyzing the development of local strain in paper we found that regions with higher basis weight and higher fiber orientation in load direction tend to exhibit considerably lower strain during tensile testing. Furthermore, the relation between local strain and local grammage can be predicted with the statistical theory of elasticity. Also regions with higher density have lower local strain, but not as pronounced. The findings for local fiber–fiber bond failure of paper are similar but not equivalent. The strongest correlation exists with local grammage. Local density and local fiber orientation show in turn weaker correlation with local bond failure. Local variations in paper thickness were not relevant in any case. These findings are highlighting the relevance of local fiber orientation and local density variations as structural mechanisms governing paper failure. In the past the focus has been mostly on paper formation. Together with local grammage (formation) they are responsible for the weak spots in paper, and thus cause local concentrations of paper strain and the initiation of failure under tensile load. [ABSTRACT FROM AUTHOR]

Biofiber is an extensive and renewable raw material, whose products meet the demands of constructing an environmental-friendly and resource-favorable society. As a typical biofiber assembly, paper inherits its characteristics and may lose its mechanical properties after prolonged contact with water, leading to a material failure. Here, we report an environment friendly waterproof composite by a simple surface treatment. This composite is creatively prepared via a formation of rough microstructures for ink micro-aggregates on the ink-brushed paper, of which this bio-inspired structure is beneficial to hydrophobic properties and light capture capability. Specifically, it possesses excellent hydrophobicity with a high contact angle over 150° and photothermal performance with a solar evaporation rate of 1.324 kg m−2 h−1 under 100 mW/cm2. In addition, it reveals superior waterproof and deicing performance, decreasing the icing adhesion time to 63 s under 100 mW/cm2. Additional advantages include durability, designability, and large-area production. In view of these excellent properties, this waterproof photothermal material holds a bright prospect in the fields of solar evaporation, deicing device, packaging, and so forth. [ABSTRACT FROM AUTHOR]

Graphene-based nanomaterials have found significant interest in the development of embedded sensors to monitor the fracture behavior in composite structures. In this work, in-situ crack propagation and fracture behavior within a glass fiber reinforced polymer composite (GFRP) was monitored using embedded reduced graphene oxide (rGO) coated fabrics and highly conductive graphene nanoplatelet (GnP) paper. All laminates were fabricated using the resin infusion process. The piezoresistive performance of both types of laminates was evaluated using in-plane and out-of-plane mechanical tests. The effect of GnP paper thickness (50/150/240 µm) and loading rate was also evaluated using tensile and Mode-I fracture loadings. Piezoresistivity of the sensors was reduced by increasing loading rate during tensile tests. All laminates with GnP paper exhibited poor mechanical performance under tensile loading. The laminates with 50 µm GnP paper showed highest sensitivity under Mode-I loading. In comparison to pristine laminates, the interlaminar fracture toughness of laminates with 50 µm GnP paper was reduced by 70%. Furthermore, laminates with rGO coated fabrics demonstrated stable crack propagation under Mode-I loading as compared to GnP based laminates. The fractured surfaces were analyzed using scanning electron microscopy to investigate the underlying fracture mechanisms of the sensors in the composite laminates. [Display omitted] • Composites with embedded GnP paper and rGO coated fabric sensors were manufactured. • Sensor based on thin GnP paper was found more sensitive than the thick GnP sensors. • Loading rate and thickness effects on the sensing behavior were characterized. • Increasing the load rate during in-plane tensile tests decreases the sensitivity. • rGO based sensor exhibited high mechanical properties than the GnP based sensors. [ABSTRACT FROM AUTHOR]

: We analyze 6500 mm long fracture lines of paper as an example of crack propagation involving disorder. The cracks are asymptotically self-affine, with a roughness exponent close to 0.6. Systematic deviations from the power-law-scaling exist below a lengthscale related to the microscopic heterogeneities and possibly to a cross-over from 3d to 2d crack propagation. Several analysis methods are discussed, including first return analysis and the detection of correlated trends. [ABSTRACT FROM AUTHOR]

Introduction: Cracks, as structural defects or fractures in materials like concrete, asphalt, and metal, pose significant challenges to the stability and safety of various structures. Addressing crack detection is of paramount importance due to its implications for public safety, infrastructure integrity, maintenance costs, asset longevity, preventive maintenance, economic impact, and environmental considerations. Methods: In this survey paper, we present a comprehensive analysis of recent advancements and developments in crack detection technologies for structures, with a specific focus on articles published between 2022 and 2023. Our methodology involves an exhaustive search of the Scopus database using keywords related to crack detection and machine learning techniques. Among the 129 papers reviewed, 85 were closely aligned with our research focus. Results: We explore datasets that underpin crack detection research, categorizing them as public datasets, papers with their own datasets, and those using a hybrid approach. The prevalence and usage patterns of public datasets are presented, highlighting datasets like Crack500, Crack Forest Dataset (CFD), and Deep Crack. Furthermore, papers employing proprietary datasets and those combining public and proprietary sources are examined. The survey comprehensively investigates the algorithms and methods utilized, encompassing CNN, YOLO, UNet, ResNet, and others, elucidating their contributions to crack detection. Evaluation metrics such as accuracy, precision, recall, F1-score, and IoU are discussed in the context of assessing model performance. The results of the 85 papers are summarized, demonstrating advancements in crack detection accuracy, efficiency, and applicability. Discussion: Notably, we observe a trend towards using modern and novel algorithms, such as Vision Transformers (ViT), and a shift away from traditional methods. The conclusion encapsulates the current state of crack detection research, highlighting the integration of multiple algorithms, expert models, and innovative data collection techniques. As a future direction, the adoption of emerging algorithms like ViT is suggested. This survey paper serves as a valuable resource for researchers, practitioners, and engineers working in the field of crack detection, offering insights into the latest trends, methodologies, and challenges. [ABSTRACT FROM AUTHOR]

Abstract  In this study, a simplified Acoustic Emission (AE) equipment, in essence an AE signal conditioner and a USB (Universal Serial Bus) data acquisition system, is used to study what happens in paper structures during mechanical loading. By the use of such equipment, some parameters that can be extracted are e.g. the stress and strain at onset of AE, the stress and strain at the onset of rapid AE defined as some numerical factor (larger then one) times the initial emission rate, the emission rate at the first stage of loading and the stress and strain at final failure i.e. when the specimen loses its load carrying ability.In this study however, the interest is focused on one particular parameter i.e. the elastic strain energy density W c at onset of AE. This is a parameter with a clear physical meaning and in this study, the correlation between this parameter and a fracture toughness measure, is investigated.The conclusion is that when nine different paper materials (with a large span regarding properties) are considered, there is a correlation (however not linear) between these two parameters. [ABSTRACT FROM AUTHOR]

2D materials < such > as planar fibrous networks exhibit several mechanical peculiarities, which we here decipher through a 3D-to-2D transition in the framework of continuum micromechanics or random mean-field homogenization theory. Network-to-fiber concentration (or "downscaling") tensors are derived from Eshelby–Laws matrix-inclusion problems, specified for infinitely long, infinitely flat fibers, and for infinitely flat spheroidal pores of vanishing stiffness. Overall material failure is associated with microscopic shear failure orthogonal to the fiber direction. Corresponding structure–property relations between porosity on the one hand, and in-plane stiffness as well as strength on the other hand, appear as linear. This is in good agreement with mechanical experiments carried out on pulp fibers, on pulp fiber-to-pulp fiber bonds, and on corresponding paper sheets. • A theoretical model has been developed that is able to predict the macroscopic mechanical behavior of planar transversely isotropic fiber networks out of the properties of fibers and fiber-to-fiber bonds leading to their formation. • An explicit, closed-form expression for the Hill morphology tensor of an infinitely thin oblate spheroidal inclusion embedded into a transversely isotropic, as well as an innovative numerical approach to treat associated singularities, have been used. • The model is computationally highly efficient and effective, being capable of quickly predicting the mechanical properties of virtually any planar transversely isotropic fiber network. • Theoretically predicted data for the case of wood-based paper sheets, computed from experimentally determined properties of pulp fibers and pulp fiber-to-pulp fiber bonds leading to their formation, are shown to be in good agreement with experimentally determined mechanical data for the very same paper sheets. [ABSTRACT FROM AUTHOR]

Centre-notched tension and double-edge-notched tension tests were conducted using specimens of copy paper in order to determine the Mode I critical J -integral. The crack length was varied during the test, and the effects of the test method and crack length were examined. The critical J -integral obtained from the centre-notched tension test was significantly smaller than that obtained from the double-edge-notched tension test. In both tests, the critical stress intensity factor decreased as the initial crack length increased. When the crack length correction was performed, however, the Mode I critical J -integral could be accurately obtained while reducing the aforementioned dependencies. [ABSTRACT FROM AUTHOR]

We study the mechanical response, and tearing features of crêpe paper, a two-dimensional, very anisotropic material, with one direction much less stiff than the other one. Depending on how the soft direction has been pre-stretched or not, the apparent Young modulus of the material can be varied over a broad range, while its fracture energy remains unaltered. The classical tearing concertina problem shows that a macroscopic measurement (the shape of the teared region) provides a direct access to the fracture properties of the material (effective Young's modulus, and fracture energy). The overall discussion is conducted in the frame of Griffith's theory of fracture. [ABSTRACT FROM AUTHOR]

Attending in-class paper demonstrations and performing experiments in solid mechanics courses are very effective ways for students to gain an understanding of the complicated concepts of mechanics. This paper explores a few applications of dogbone tensile tests, stress concentrations and crack kinking or mixed-mode fracture. Furthermore, this handy technique can be extended to other broader areas of mechanics education. Since only simple materials and supplies are used, copy paper, staples, scissors and a paper punching machine, students can repeat these typical mechanics experiments in future in other locations, such as in an office or at home. Therefore, this simple and effective technique can have a remarkable influence on the student's long-term career. [ABSTRACT FROM AUTHOR]

The “essential work of fracture” (EWF) method is applied to various machine-made papers. The deforming and fracturing processes of the paper samples during testing is analyzed by means of the thermographic observation. Plastic deformation zone appears in three ways when deep double edge notched tension specimens are strained under in-plane stress: i.e. 1. type (i)--appearing through whole the ligament in a vague manner and developing into a circular (or oval) zone even before or at the maximum load point; 2. type (ii)--appearing from notch tip and amalgamating into a circular (or oval) zone after the maximum load point; and 3. type (iii)--appearing from notch tip and not amalgamating into a circular (or oval) zone until the sheet failure. Specimens with small ligament length (L) are likely to belong to type (i), while those with large L to type (ii) & (iii). Among these three types, type (i) fulfills the original assumption of the EWF method best in terms of the complete ligament yielding before crack initiation. Thus the specific essential work of fracture determined using the linear relation of type (i) should be correct, although the estimated work is a little smaller than that from the linear relation of type (ii) & (iii). [ABSTRACT FROM AUTHOR]

Graphene origami (G-ori) can possess unique mechanical properties and achieve some distinctive functionalization by engineering their configurations. However, it remains a tremendous challenge to modulate its formation and properties at the micro- and nano-scales. Herein, we systemically present the formation of G-ori activated by creased marks via molecular dynamics (MD) simulations. The pre-existing creased mark in graphene is created in a controlled way by transforming sp 2 to sp 3 bonds at the crease. Our results show that the presence of interlayer sp 3 bonds at the crease can direct crack growth and hence pave a new way to tailor graphene sheets into specified pieces. The crease also guides the folding process of graphene into various geometric configurations. Sophisticated G-ori can be constructed by designing rational crease distribution on the graphene surface. Checking against the folding process of paper origami shows that the crease-induced targeted folding can be achieved at both nano- and macro-scales in exactly the same way. Our findings provide a simple and feasible method to construct graphene-based nano-devices by designing rational morphological configurations of G-ori. Image 1 [ABSTRACT FROM AUTHOR]

Abstract: Continuum damage mechanics (CDM) is used to describe the post-elastic behavior of low-basis-weight paper. The relevance of undertaking studies of the mechanical behavior of low-basis-weight paper is that it enables characterization, optimization and quality control. In accordance with a CDM theory, an internal variable is introduced that represent the degree to which the material has degraded in a continuum sense and details inherent in a damage evolution law contain information about the rupture mechanism. To account for long ranging micro-structural effects, because of the fiber structure in the paper material, a non-local formulation of the constitutive law is considered. Of particular interest is the fracture toughness of the material, i.e. the ability to resist further crack propagation, as it is often a good measure of flaw tolerance and durability in the context of paper. The constitutive model discussed is verified against tensile tests on rectangular paper specimens containing pre-fabricated cracks. Acoustic emission was used to study the damage evolution in paper specimens during tensile loading. An orthotropic material description has been utilized. The model is contrasted with a purely isotropic formulation. It seems that for the type of problem analyzed in this work, an orthotropic material description does not significantly improve the predictive capability as compared to an isotropic formulation. It is concluded that the model can be used to evaluate the influence of arbitrary defect geometries, defect size and loading conditions and can easily be incorporated into a finite element code. [Copyright &y& Elsevier]

The emergence of graphene paper comprising well-stacked graphene flakes has promoted the application of graphene-based materials in diverse fields such as energy storage devices, membrane desalination, and actuators. The fundamental properties of graphene paper such as mechanical, electrical, and thermal properties are critical to the design and fabrication of paper-based devices. In this study, the interlayer interactions in graphene paper were investigated by double cantilever beam (DCB) fracture tests. Graphene papers fabricated by flow-directed stacking of electrochemically exfoliated few-layer graphene flakes were mechanically separated into two parts, which generated force-displacement responses of the DCB sample. The analysis based on fracture mechanics revealed that the interlayer separation energy of the graphene paper was 9.83 ± 0.06 J/m2. The results provided a fundamental understanding of the interfacial properties of graphene papers, which will be useful for developing paper-based devices with mechanical integrity. [ABSTRACT FROM AUTHOR]

The article presents a reply by S. Venkatesh and colleagues to comments made by J. R. Marko and D. B. Fissel about their study, On the Deterioration of Icebergs in the Marginal Ice Zone. According to Venkatesh and colleagues, Marko and Fissel point to the many difficulties and expense in obtaining the necessary data to predict the deterioration of icebergs in an operational time setting. They pointed out that they are confident of the calculated deterioration rates. They said that while the calved iceberg fragments under the existing environmental conditions constitute only 2 to 3% of the original masses, the deterioration rates will increase with increasing water temperatures and sea state conditions.

The mechanical properties of wood fiber-based, commercial papers and metal foils are qualitatively similar, and their plane stress, Mode I crack growth resistances have not been reliably correlated with single-valued fracture mechanics parameters for centimeter-scale specimens. Experimentally-measured crack tip strain fields of Mode I cracks growing in commercial paper were used to define a three-stage, steady-state crack growth mechanism. Immediately upon loading, the net sections ahead of the cracks yielded. As the cracks began to grow, well-defined zones of (incremental) active plasticity (ZAPs) formed within the yielded ligaments. Cracks transitioned to steady-state growth with an average characteristic stress, σ c , of 20.9 MPa. In contrast to metallic foils, the characteristic stress in steady-state cracks in paper was offset by 8.3 MPa due to a 1.9 mm fiber bridging zone that scaled with the average fiber agglomerate (floc) size. The fiber network structure also induced a large, reversed steady-state zone in the crack wakes. While reversed ZAPS were previously predicted by numerical models of plane strain Mode I and III cracks under small-scale yielding conditions, they were never observed experimentally and were neglected. The types and evolution of the cumulative and incremental plastic zones in paper defined appropriate paths for steady-state J -integral calculations. [ABSTRACT FROM AUTHOR]

Novel sandwich composites made of syntactic foam core and paper skin were developed as potential building materials. Interface bonding between core and skin was controlled by varying starch content. Two different microsphere size groups were employed for syntactic foam core manufacturing based on the pre-mold processing method. Properties of skin paper with starch adhesive on were found to be affected by drying time of starch adhesive. Mechanical behavior of manufactured sandwich composites in relation with properties of constituent materials was studied. Skin paper contributed to increase up to 40% in estimated flexural strength over syntactic foams, depending on starch content in adhesive between syntactic foam core and paper skin. Small microsphere size group for syntactic foam core was found to be advantageous in strengthening of sandwich composites for a given starch content in adhesive. This finding was in agreement with calculated values of estimated shear stress at interface between skin and core. Failure process of the sandwich composites was discussed in relation with load–deflection curves. Cracking of syntactic foam core was detected to be the first event in sandwich composite failure sequence. Hygroscopic behavior of syntactic foam panels was investigated. Moisture content in the foam was measured to be high for high starch content in the foam panels. No significant moisture effect on flexural strength of syntactic foam panels after being subjected to moisture about 2 months was found for both microsphere size groups. However, substantial decrease (28%) in flexural modulus was found for the foam panels made of large microspheres although not much moisture effect was found on that of small microspheres. [ABSTRACT FROM PUBLISHER]

B. Palmieri et al. in "Investigation on Stress Relaxation of Discontinuous Recycled/Repurposed Carbon Fiber Composites" investigate the thermo-mechanical and viscoelastic behavior of composites made at different recycled carbon fiber (rCF) content. These are similar in structure to carbon fiber composites, where the matrix features dielectric characteristics, making the structure capable of storing electric energy. This special issue focus is dedicated to the fourth edition of the "International Symposium on Dynamic Response and Failure of Composite Materials, Draf2022" held in Ischia, Naples, from June 21-24, 2022. [Extracted from the article]

The fracture behaviors of graphene oxide (GO) and GO/multi-walled carbon nanotube (MWCNT) hybrid papers are studied in both quasi-static mode-I opening and mode-III tearing fracture. Large GO papers give rise to a higher energy release rate and tearing toughness than those made from small GO sheets: about 36% and 70% enhancements are shown for the large GO papers due to a more compact structure and better GO sheet alignment. Hybridization of GO papers with MWCNTs also improves these properties when up to 5 wt.% of MWCNTs is incorporated, attributed to the stronger GO interlayer bonds through π-π interactions with intercalated MWCNTs. Fracture surface examination indicates that cleavage failure prevails in mode-I fracture depending on the size of GO sheets: the unsorted and large GO papers fail mainly by brittle cleavage of GO sheets whereas small GO papers fail by combined brittle cleavage and minor pullout following debonding of GO bundles. In contrast, combination of cleavage and debonding failures is dominant in mode-III fracture of GO papers, regardless of GO size. The torn edges present typical characteristics of a saw-tooth wave with disordered oscillation where the large GO papers exhibit generally higher amplitude peaks than the small GO papers. [ABSTRACT FROM AUTHOR]

The degree of polymerization (DP) has been regarded as an important symbol of mechanical strength, reflecting the aging condition of transformer insulation paper. In this article, a new concept called fracture degree is proposed on the basis of DP. First, nine cellulose Iβ crystal models with different fracture degrees were built. Then relevant mechanical parameters and hydrogen bond numbers were calculated by molecular dynamics (MD) simulation. Results showed that during the aging process of insulation paper with fracture of cellulose chain, the elastic constant C33 produces appreciable impact on the Young's modulus (E). With the decrease of DP and increase of fracture degree, the Young's modulus step decreases. To the 50% and 100% fracture degree models respectively, the relationship between their different degrees of polymerization and Young's modulus is subjected to similar exponential distributions. With the increase of the fracture degree, the average hydrogen bond number drops, and the change rules apply to the Young's modulus. Since hydrogen bond is the main factor of mechanical strength, it can be inferred that the fracture degree influences mechanical strength seriously. [ABSTRACT FROM AUTHOR]

The dependence of the fracture toughness of two-dimensional (2D) elastoplastic lattices upon relative density and ductility of cell wall material is obtained for four topologies: the triangular lattice, kagome lattice, diamond lattice, and the hexagonal lattice. Crack-tip fields are explored, including the plastic zone size and crack opening displacement. The cell walls are treated as beams, with a material response given by the Ramberg-Osgood law. There is choice in the criterion for crack advance, and two extremes are considered: (i) the maximum local tensile strain (LTS) anywhere in the lattice attains the failure strain or (ii) the average tensile strain (ATS) across the cell wall attains the failure strain (which can be identified with the necking strain). The dependence of macroscopic fracture toughness upon failure strain, strain hardening exponent, and relative density is obtained for each lattice, and scaling laws are derived. The role of imperfections in degrading the fracture toughness is assessed by random movement of the nodes. The paper provides a strategy for obtaining lattices of high toughness at low density, thereby filling gaps in material property space. [ABSTRACT FROM AUTHOR]