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Aluminoborate glass, recognized for its remarkable crack resistance, presents significant potential as a cover material for portable electronic devices. Nevertheless, its relatively low hardness has been a limiting factor. This study synthesized a series of 11 Li 2 O-30 Al 2 O 3 -(55-x) B 2 O 3 -2 TiO 2 -2 P 2 O 5 -xCaO (wt%), with x varying from 0 to 10, employing the melt-cast method. The resultant glass-ceramics were produced via heat treatment at 590 °C for 2 h, followed by a systematic examination of their structural and mechanical properties. The investigation demonstrated that an increase in CaO content diminishes crystallization and induces a morphological transition in the crystalline phases from granular and short rod-like structures to lath-like formations, which subsequently impacts the coordination environment of Al and B atoms. With a CaO content of 2 %, the GC2 sample precipitated Li(Al 7 B 4 O 17) and Li 2 AlB 5 O 10 phases, achieving a compressive strength (CR) value of 15.0 N, a hardness of 7.51 GPa, and a fracture toughness of 1.50 MPa m0.5. This glass-ceramic exhibited optimal scratch resistance and visible light transmittance exceeding 85 %, underscoring its considerable promise for application as smartphone cover glass due to its impressive overall damage resistance. [ABSTRACT FROM AUTHOR]

This study investigates the effectiveness of polyether block amide (PEBA) thermoplastic elastomeric nanofibers in reducing low-velocity impact damage across three carbon fiber composite lay-up configurations: a cross-ply [0°/90°]2s (CP) and a quasi-isotropic [0°/45°/90°/−45°]s (QI) lay-up utilizing unidirectional plies, and a stacked woven [(0°,90°)]4s (W) lay-up using twill woven fabric plies. The flexural strength and interlaminar shear strength of the composites remained unaffected by the addition of nanofibers: around 750 MPa and 63 MPa for CP, 550 MPa and 58 MPa for QI, and 650 MPa and 50 MPa for W, respectively. The incorporation of nanofibers in the interlaminar regions resulted in a substantial reduction in projected damage area, ranging from 30% to 50% reduction over an impact energy range of 5–20 J. Microscopic analysis showed that especially the delamination damage decreased in toughened composites, while intralaminar damage remained similar for the cross-ply and quasi-isotropic lay-ups and decreased only in the woven lay-up. This agrees with the broad body of research that shows that interleaved nanofibers result in a higher delamination resistance due to toughening mechanisms related to nanofiber bridging of cracks. Despite their ability to mitigate delamination during impact, nanofibers showed limited positive effects on Compression After Impact (CAI) strength in quasi-isotropic and cross-ply composites. Interestingly, only the woven fabric composites demonstrated improved CAI strength, with a 12% improvement on average over the impact energy range, attributed to a reduction in both interlaminar and intralaminar damage. This study indicates the critical role of fiber integrity over delamination size in determining CAI performance, suggesting that the delaminations are not sufficiently large to induce buckling of sub-layers, thereby minimizing the effect of nanofiber toughening on the CAI strength. [ABSTRACT FROM AUTHOR]

Summary: Variation in leaf venation network architecture may reflect trade‐offs among multiple functions including efficiency, resilience, support, cost, and resistance to drought and herbivory. However, our knowledge about architecture‐function trade‐offs is mostly based on studies examining a small number of functional axes, so we still lack a more integrative picture of multidimensional trade‐offs.Here, we measured architecture and functional traits on 122 ferns and angiosperms species to describe how trade‐offs vary across phylogenetic groups and vein spatial scales (small, medium, and large vein width) and determine whether architecture traits at each scale have independent or integrated effects on each function.We found that generalized architecture‐function trade‐offs are weak. Architecture strongly predicts leaf support and damage resistance axes but weakly predicts efficiency and resilience axes. Architecture traits at different spatial scales contribute to different functional axes, allowing plants to independently modulate different functions by varying network properties at each scale.This independence of vein architecture traits within and across spatial scales may enable evolution of multiple alternative leaf network designs with similar functioning. [ABSTRACT FROM AUTHOR]

Spores are the biological structures formed out of sporulation from vegetative cells in adverse conditions. Being tolerant to many extreme environment and conditions, they escape and survives critical processing steps in the food industry that poses food and health safety problems, as is evident from the increase in reports of food-borne outbreaks due to spore-formers. Electromagnetic radiation (EM) is used for rapid decontamination and sterilization purposes in the food industry. Many studies have reported a greater reduction in spore population upon irradiation with EM rays due to its impact on genomic material and other components of spores that destabilises overall structure and brings clonogenic death. However, there is scattered literature regarding the mechanism of its inactivation and resistance against such damage. This review attempts to concisely evaluate the potential of electromagnetic radiations in spore inactivation and details its mechanism through a collective study of scientific results and reports. It also briefs about the process of sporulation, the structure of spores and the role of its components in the resistance of spores to damage. Many studies, which demonstrated that combining various EM treatments might be an effective way for inactivation of spores, were discussed in detail.

The topological attributes of fracture networks in limestone, subject to intense hydrodynamics and intricate geological discontinuities, substantially influence the mechanical and hydraulic characteristics of the rock mass. The dynamical evolution of fracture networks under stress is crucial for unveiling the interaction patterns among fractures. However, existing models are undirected graphs focused on stationary topology, which need optimization to depict fractures' dynamic development and rupture process. To compensate for the time and destruction terms, we propose the damage network model, which defines the physical interpretation of fractures through the ternary motif. We focus primarily on the evolution of node types, topological attributes, and motifs of the fracture network in limestone under uniaxial stress. Observations expose the varying behavior of the nodes' self-dynamics and neighbors' adjacent dynamics in the fracture network. This approach elucidates the impact of micro-crack behaviors on large brittle shear fractures from a topological perspective and further subdivides the progressive failure stage into four distinct phases (isolated crack growth phase, crack splay phase, damage coalescence phase, and mechanical failure phase) based on the significance profile of the motif. Regression analysis reveals a positive linear and negative power correlation between fracture network density and branch number to the rock damage resistance, respectively. The damage network model introduces a novel methodology for depicting the interaction of two-dimensional (2D) projected fractures, considering the dynamic spatiotemporal development characteristics and fracture geometric variation. It helps dynamically characterize properties such as connectivity, permeability, and damage factors while comprehensively assessing damage in rock mass fracture networks.

Highlights This work proposes three Bouligand‐inspired layups to enhance low velocity impact (LVI) damage resistance and tolerance of convectional aircraft composite laminates. Two Bouligand‐like (HL and HL_S) and one hybrid design layup, merging conventional and Bouligand architecture (HYB), were produced by vacuum bag infusion. Their performance under LVI, at 13.5, 25 and 40 (J), and compression after impact (CAI) tests were evaluated and compared with a conventional aircraft multidirectional layup (LS) produced under identical conditions. Results demonstrated that, especially for the higher impact energy levels, both Bouligand‐like laminates consistently outperformed all the other configurations, exhibiting higher load bearing capacity (peak load) and energy absorption. Additionally, the rough and poorly defined interlaminar region of Bouligand‐like layups have showed to delay severe damage for higher loads and energies, dissipating all (at 13.5 J) or most of the impact energy (more than 50%) through subcritical damage mechanisms. Compared with LS laminate, Bouligand‐inspired layups postponed the onset of severe damage thresholds by up to 120% in load and 66% in energy (HL laminate) while developing smaller and more localized damages. The high number of fibers aligned in the loading direction of LS laminate led to better damage tolerance. Vacuum bag infused Bouligand‐like laminates consistently demonstrated superior performance than the conventional aircraft multidirectional layup, exhibiting higher load bearing capacity and energy absorption, particularly at higher impact energy levels; The rough and poorly defined interlaminar region observed in both Bouligand‐like layups demonstrated to play an essential role in the efficiency of damage mechanisms, dissipating all (at low impact energy levels) or more than 50% of impact energy on subcritical damages, such as translaminar matrix cracking; Compared with the conventional layup, HL Bouligand‐like laminate postponed 120% and 66% load and energy severe damage onset thresholds; The high number of fibers aligned in the loading direction of LS laminate led to better damage tolerance, despite the larger damaged areas observed. [ABSTRACT FROM AUTHOR]

This paper describes a new interleaving methodology to improve composite laminates' low velocity impact (LVI) damage resistance. The approach relies on analyzing interlaminar stress in a conventional aircraft laminate to determine the appropriate interleaving strategy. A model was built to identify the larges interlaminar stress, and two interleaving strategies were defined, normal and shear stress. Four thin interleaving veils were used to validate strategies. Non‐ and interleaved laminates were submitted to LVI tests at 13.5, 25 and 40 (J) of energy. Despite interleaved laminates revealed an increase in thickness and resin volume fraction compared to the reference, they were limited to 10% and 7.6% on shear stress interleaved layups. Interleaved laminates also demonstrated an improved external and internal LVI damage resistance, especially when shear stress interleaving strategy was adopted, preventing external damage and mitigating internal damage up to 59%. No correlation between the veil's type and impact damage demonstrates the importance of interleaving strategies over the veil's characteristics. Highlights: Simplified quasi‐static elastic Abaqus model identified the largest in‐plane normal (axial and transversal) and shear interlaminar stresses;Four thin veils were used to validate interleaving strategies adopted;All laminates were produced using the same conditions to minimize process influence on experimental tests;Under low velocity impact (LVI) tests, interleaving laminates in the largest shear stress interlaminar can prevent external damage and mitigate internal damage up to 59%, comparing to the reference;No correlation between the veils and damage demonstrates the relevance of the interleaving strategy over the veil type. [ABSTRACT FROM AUTHOR]

In this paper, nine different carbon fiber laminates containing clusters are designed using the ant colony ACO algorithm, which have similar equivalent bending stiffnesses and B‐matrices, with the differences being the fiber orientation of the clusters and the position of the clusters in the laminates. The dynamic mechanical characterization of laminates for low velocity impact (LVI) at three different energies was carried out by means of a falling weight impact experiment. The experimental results show that the main form of failure of the laminate is delamination failure at low energy impacts, and shear fracture becomes more and more obvious with the elevation of the impact energy, which was observed in detail by the stereo microscope and electron microscope. The damage area of the laminate and the force and displacement curves after 30 J energy impact were compared by x‐ray scanning to derive the effects of the angle of the ply cluster fibers and the different positions of the ply clusters in the laminate on the impact resistance of the laminate. In conclusion, when designing the laminate, consideration should be given to designing 45° clusters on the impacted side and 90° clusters in the middle layer of the laminate to obtain the best impact resistance. Highlights: Designed 9 types of laminates with different laminate structures based on ACO algorithm.Different laminates have similar equivalent bending stiffnesses and the B matrix as close to 0 as possible.LVI tests at three energies were performed on 9 types of laminates.The effects of different orientations of the clusters and the position of the clusters in the laminate on the impact resistance of the laminate were investigated. [ABSTRACT FROM AUTHOR]

The performance damage of newly placed concrete caused by vehicle–bridge coupling vibration is an inevitable phenomenon among widening of existing concrete bridge. Calcium sulfoaluminate cement-based engineered cementitious composite (CSA–ECC) was proposed to replace the conventional concrete to address the aforementioned issues. The effects of vehicle–bridge coupled vibration (involve the frequency and the amplitude) on the mechanical properties of CSA–ECC including compressive strength, flexural strength and flexural toughness were investigated. The distribution of air bubbles was analyzed by X-ray micro-computed tomography (X-ray CT) to explore the mechanism of vibration affecting the mechanical properties of CSA–ECC. The results indicate that the volume percentage of coarse air bubbles (>1.0 mm3) decreases from 54.70 to 25.94%, and the volume percentage of micro air bubbles (0–0.2 mm3) increases from 30.89 to 54.19%. As a result, the microstructure of matrix and fiber/matrix interface are densified due to the redistribution of air bubbles caused by the coupling vibration. Therefore, the application of vibration significantly enhances the flexural strength and flexural toughness of CSA–ECC, ascribing to stronger matrix fracture toughness and fiber/matrix interfacial frictional bond. These indicate that the CSA–ECC has a promising application scenario in highway bridge widening projects with exceptional vibration-induced damage resistance ability. [ABSTRACT FROM AUTHOR]

Empirical and theoretical evidence suggests that getting injured during combat decreases an individual's chances of winning. Thus, it has been hypothesized that species that engage in injurious fights may evolve armour. However, much remains unknown about the role that male–male combat has in promoting the evolution of such damage-reducing structures. Here, we tested the hypothesis that male–male combat can increase the damage resistance of structures using the giant mesquite bug, Pachylis neocalifornicus. When males in this species fight over access to mates, they use their weaponized hindlegs to puncture the dorsal side, but not the ventral side, of their rivals. We found that structures on the dorsal side of males could generally withstand the forces of combat, while structures on the dorsal side of females could not. The sexual dimorphism in damage resistance was location dependent because structures on the ventral side of both males and females also could not withstand the forces of combat. Thus, males appear to only increase their defensive capacity in the locations where strikes from rivals normally land. These results provide evidence that male–male combat can promote the evolution of damage-reducing structures (i.e. sexually selected shields). Moreover, the relatively inconspicuous nature of the sexually selected shields in this species suggests that defensive traits related to combat may be more common than currently considered. • We tested damage resistance of structures in the fighting insect P. neocalifornicus. • Male cuticle was harder to puncture than female cuticle. • Sexual dimorphism in damage resistance was location dependent. • Male armour can withstand some, but not all, fighting-related forces. [ABSTRACT FROM AUTHOR]

Carbon composites are susceptible to invisible damage development such as matrix cracking, fiber kinking, and interfacial debonding upon external transverse loading. These incipient damages may interact to evolve into life‐limiting delamination propagating both in in‐plane and transverse directions. This study addressed that by interleaving carbon/epoxy composites with electrospun nylon 6 nanofibers adopting a double infusion method. Damage resistance results showed that the optimum nanofiber areal weight (17.35 g/m2) offered a 27% improvement in specific total toughness. The emergence of pseudo‐ductility substantially enhanced the plastic toughness (46.15%) of interleaved composites. The load required for initial matrix cracking was 65.49% higher, and number of matrix cracking events was suppressed by 84.11% at the optimum areal weight of interleave. Fractography revealed frequent interlaminar crossings and delamination crack bridging as two major toughness mechanisms. Both the external damage area and delaminated area increased with increment in nanofiber areal weight. Highlights: Electrospun nanofibre interleaved carbon/epoxy composites were fabricated through a double infusion method to characterize damage resistance.Acoustic data of matrix cracking was rationalized to show the effectiveness of nanofiber interleaves in suppressing this damage type.Microstructural factors and mechanisms contributing to the improved toughness of optimally interleaved composites were identified.External damage/delaminated areas of interleaved composites were correlated with nanofiber areal weights. [ABSTRACT FROM AUTHOR]

The incorporation of sustainability into the design of transport vehicles has become increasingly important in recent years. A low carbon footprint makes wood-based structures attractive to replace other lightweight materials such as aluminum or fiber-reinforced plastics. This paper investigates and compares the static and dynamic impact behavior of thin Beech wood veneer laminates in standardized mechanical tests. The results obtained from Quasi-Static Indentation (QSI) and dynamic Low-Velocity Impact (LVI) tests reveal similarities and differences with regard to load vs. displacement behavior, damage mechanisms, permanent deformation, and energy absorption. While yield strength and damage modes are comparable in both test cases, it is found that the bending stiffness is strain-rate sensitive. Plastic deformation in compression is identified as the governing mechanism for energy absorption. These results can guide the design of sustainable wood-based structures for future transport applications where a thorough understanding of impact and crashworthiness is important. [ABSTRACT FROM AUTHOR]

In the process of landscaping or afforestation in challenging terrain, in order to improve the survival rate of transplanted seedlings, it is necessary to transplant seedlings with a mother soil ball attached. During transportation, the soil ball at the root of the seedlings is very susceptible to breakage due to compression, bumps, and collisions. In order to ensure the integrity of the soil ball of the transplanted seedlings and improve the survival rate of seedlings, a method of chemically enhancing the soil surface strength was employed. Specifically, a polymer-based soil consolidating agent was used to solidify the root balls of the seedlings. To examine the abrasion resistance performance of the soil balls formed by consolidating the surface with polymer adhesive during the transportation process, we utilized a polymer-based consolidating agent to prepare test soil columns and developed a method to simulate the damage resistance performance of seedling root balls during transportation using these soil columns. The method primarily encompasses two aspects of testing: compressive strength testing of the consolidated soil columns and resistance to transportation vibration testing. The first method for testing the resistance to transportation vibration of the consolidated soil columns is a combination test that includes three sets of tests: highway truck transportation vibration testing, combined wheel vehicle transportation vibration testing, and impact testing. Although the method is cumbersome, testing is more accurate. The second method for testing the resistance to transportation vibration of the consolidated soil columns involves simultaneously testing multiple consolidated soil columns using a simulated transportation vibration test platform. The testing method is concise and efficient, and the test results are more intuitive. The combined assessment of the resistance to transportation vibration and compressive strength testing of the consolidated soil columns allows for a comprehensive evaluation of the soil columns' resistance to damage during transportation. This study mainly provides a quick and effective method for detecting the damage resistance of consolidated soil columns/balls during transportation, providing technical support for the application of polymer-based consolidation agents in the field of seedling transplantation. [ABSTRACT FROM AUTHOR]

Damage resistance of carbon fibre reinforced composites is crucial parameter to be considered at both primary selection and in-service maintenance stages. High stiffness of carbon-epoxy system and stacked configuration make it susceptible to impact induced brittle damages. Delamination is one such life-limiting damage modes that can severely inhibit load carrying capacity of laminates. Hence to improve the damage resistance of composites demands tailoring tough microstructure and altering brittle damage modes with ductile ones. This work attempted to design damage resistant carbon composites through modification of epoxy matrix with amine functionalized multi walled carbon nanotubes (NH2-MWCNT). Laminates with different nanotube concentrations (0.3, 0.6, 0.9 and 1.2 wt. %) were fabricated to investigate its influence on load bearing capacity, toughness and damage resistance of fibre reinforced nanocomposites. Generally, peak force, displacement and toughness until maximum force improved at all nanoparticle concentrations. Matrix cracking was suppressed owing to optimum cross-linking of nanoparticle with matrix. External damage area increased with nanoparticle concentration although delaminated area, mapped through c-scan, was suppressed up to 27.73%. A combination of higher degree of interfacial interactions, induced by nanoparticles, and energy absorbing microstructure was concluded to be behind improvement in the damage resistance of composites.

With the application of carbon fiber reinforced plastics (CFRPs), the damage behaviors and mechanisms are desirable to understand. In this work, the Bismaleimide (BMI) matrix composites were employed to study the damage mechanism under transverse loading through quasi-static indentation, where optical microscopy, ultrasonic C-scan, and scanning electron microscope were subjected to examine the damaged regions. The results show that cracks first take place in a resin-rich interlaminar region before the loading reached to a threshold value. Then, the cracks would develop into intralaminar cracks in the fiber bundle region consisting of the shear and bending cracks. Subsequently, the cracks randomly extend to adjacent plies and result in delamination. Finally, the back surface of composites presents a remarkable ply splitting and fiber breakage under increasing loading. Furthermore, conical-shaped indentation patterns in cross-sectional and the undamaged zone under the indenter suggest the BMI matrix composites possess potential applications in engineering materials with a superior stress-releasing structure.

The present paper investigates the response a sandwich composite laminate that involves intraply hybrid carbon fiber reinforced polymer (CFRP)/Dyneema core under impact and post-impact tests. This intraply hybrid core was designed to gain the high elasticity and high stiffness/weight ratio of Dyneema fibers while maintaining the structural integrity of CFRP at the laminate core. Low-velocity impact and compression after impact tests were employed to evaluate the damage resistance and tolerance of the laminates. Micro-computed tomography was deployed to inspect the different modes of damage and their propagation during low-velocity impact. The results showed that the damage started in the sandwich composite as localized matrix cracks and delaminations at CFRP impacted face. However, it was distributed through the whole laminate thickness in the monolithic CFRP composites. The fiber cut initiated at 70 J impact energy for the sandwich composite at the impacted CFRP face plies as fiber kinking due to compressive stresses. However, it was initiated at the lower plies of the CFRP composite at 30 J due to high bending and normal strains. This delayed fiber breakage revealed the better residual compression after impact (CAI) strength of the sandwich composite, where it showed 33.5% improved specific CAI strength compared to the monolithic CFRP composite.

Carbon composites are sensitive to matrix cracking, delamination, and fiber‐matrix debonding induced by external transverse loading. Such invisible damages demand frequent non‐destructive testing (NDT) owing to their tendency to propagate in brittle composites. Application of carbon composites in safety critical structures have urged researchers to design for superior damage resistance. Bulk modification of matrices through nanoparticles is one such technique that exploits high surface area and mechanical properties of nano‐reinforcements to engineer desired interfaces and improve mechanical properties. This study adopts the same technique to investigate effect of electrospun nylon 6 short nanofiber addition on damage resistance of carbon fiber/epoxy composites. Different concentrations (0.05, 0.1, 0.2, and 0.4 wt% of epoxy) of short nanofibers were prepared to modify epoxy and fabricate carbon laminates. Quasi‐static indentation tests confirmed improvement of 8.7, 8.8, and 53% in peak force, displacement and elastic toughness of carbon composites at optimum nanofiber concentration (0.05 wt%). External damage area marginally improved though directional damage growth was suppressed. Delaminated area reduced by 12.6% at optimum nanofiber concentration. Suppression of compressive fiber failure and enhanced interlaminar bonding were credited to offer superior performance. In general, development of nanofiber‐rich zones declined the load bearing response above optimum concentration. [ABSTRACT FROM AUTHOR]

In this study, a novel optical limiting (OL) experimental setup is proposed for evaluating laser-induced damage thresholds (LIDTs) of materials. This technique is based on the pump–probe method, and the damage can be measured using a probe beam with a delay adjusted according to experimental conditions. Moreover, the probe beam is controlled to reach the sample before the pump beam, and the pump beam waist is larger than the probe beam waist to facilitate measurement. In particular, using this probe beam, nonlinear effects of the material can be ignored. Compared with other traditional technologies, the proposed method allows direct observation of the OL threshold of the material as well as measurement of in situ and laser damage of the material. This technique can quantify the in situ damage and LIDTs of materials effectively and conveniently. The validity of this approach is demonstrated by measuring the LIDT of ZnSe. Such measurement method enables searching for more efficient laser protective materials with high LIDTs that can be widely used in laser protection and other applications. [ABSTRACT FROM AUTHOR]

The integumentary system in animals serves as an important line of defence against physiological and mechanical external forces. Over time, integuments have evolved layered structures (scales, cuticle and skin) with high toughness and strength to resist damage and prevent wound expansion. While previous studies have examined their defensive performance under low-rate conditions, the failure response and damage resistance of these thin layers under dynamic biological puncture remain underexplored. Here, we utilize a novel experimental framework to investigate the mechanics of dynamic puncture in both bilayer structures of synthetic tissue-mimicking composite materials and natural skin tissues. Our findings reveal the remarkable efficiency of a thin outer skin layer in reducing the overall extent of dynamic puncture damage. This enhanced damage resistance is governed by interlayer properties through puncture energetics and diminishes in strength at higher puncture rates due to rate-dependent effects in silicone tissue simulants. In addition, natural skin tissues exhibit unique material properties and failure behaviours, leading to superior damage reduction capability compared with synthetic counterparts. These findings contribute to a deeper understanding of the inherent biomechanical complexity of biological puncture systems with layered composite material structures. They lay the groundwork for future comparative studies and bio-inspired applications.

Incorporating acoustic and mechanical properties into a single multifunctional structure has attracted considerable attention in engineering. However, effectively integrating these sound absorption properties and damage resistance to achieve multifunctional structural designs remains a great challenge due to imperfect design methods. In this study, the inherent mechanical properties of turtle shells by introducing dissipative pores are leveraged to present a lattice structure that possesses both excellent sound-absorbing and high damage-resistant characteristics. To achieve acoustic optimization design, a universal high-fidelity neural network correction model is proposed to address the impedance calculation challenge in complex structures. Building upon this foundation, a multi-cell combination design enables to achieve high absorption through optimization with a low thickness of 50 mm, resulting in average sound absorption coefficients reaching 0.88 and 0.93 within the frequency ranges of 300-600 Hz and 500-1000 Hz, respectively. It is also found that the optimized structures exhibit exceptional damage resistance under varying relative densities via the coupling effect of the shell thickness on the acoustic and mechanical properties. Overall, this work introduces a novel paradigm for designing intricate multifunctional structures with acoustic and mechanical properties while providing valuable inspiration for future research on multifunctional structure design., (© 2024 Wiley‐VCH GmbH.)

In this study the effects of moisture ingression on the impact damage resistance and damage tolerance of NextelTM610/alumina-silicate ceramic matrix composites were experimentally evaluated. Thin and thick composite laminates with balanced and symmetric layups were placed inside an environmental chamber at 80°C and 85% relative humidity till moisture saturation was reached. The laminates were then subjected to low velocity impacts using a hemispherical steel impactor at energy levels of 2.5 J and 10 J for the thin and thick laminates, respectively. This resulted in similar damage depths on the impactor side between the two sets of laminates. The resultant damage was characterized non-destructively with the damage metrics of external dent area, dent depth and planar internal damage area quantitatively determined. Impacted laminates were subject to in-plane compression loading and the residual strengths were evaluated. Planar internal damage area was larger for the moisture exposed laminates in comparison to their pristine counterparts for both the thin and thick laminates. Also, larger internal damage area resulted in lower compression-after-impact strength and thus, less damage tolerant laminates. This was true for the pristine and moisture exposed cases for both the laminate thicknesses. [ABSTRACT FROM AUTHOR]

Hierarchically porous Al 2 O 3 ceramics with a porosity of 30–69% containing small intergranular pores and large pores created by a pore-forming agent were fabricated by gel-casting followed by partial sintering with starch addition. The influence of various pore types on the mechanical and thermal shock properties of the ceramics was subsequently investigated. A thermal shock parameter K was introduced to evaluate the dependence of strength degradation rate on the thermal shock temperature difference, and a new method for calculating the intergranular porosity and extrinsic porosity of the porous ceramics was developed. A low thermal shock strength degradation rate was obtained at a high ratio of fracture toughness (K IC) and elasticity modulus (E) of the material, which was achieved by decreasing the relative fraction of spheroidal extrinsic pores. However, the presence of these pores increased both the K IC and E values. [ABSTRACT FROM AUTHOR]

The present study deals with the behaviour of angle ply composite laminates subjected to low velocity impact. The laminates were prepared by E-glass fibres as reinforcement and epoxy as resin. Experiments were performed on these laminates by using low velocity drop weight set-up machine at three energy levels produced by using two masses. At energy level it was noticed that, [0/90]s laminate was most damage resistant and [0/15]s laminate was least resistant while the contact duration of impactor on laminate(s) was found to be sensitive to mass level. Finite Element (FE) analysis was performed to quantify the damage in laminates and investigate energy absorbed in intra-layer failure modes. During the post-processing FE analysis helps to mark the critical load points on the load-displacement history and quantification of distinct failure modes. The size of delamination profile was seen to be governed by fibre orientation and inter-laminar shear stresses at the interface. [ABSTRACT FROM AUTHOR]

The damage resistance of grain kernels to external loading is useful for optimizing agricultural equipment design and adjusting operational settings. This study aims to quantify and compare the damage resistance of corn and wheat kernels under different types of loading and fit the data with statistical models. The damage resistance of corn and wheat kernels to compression, friction, and repeated impacts was measured using a universal testing machine, pin-on-disk tribometer, and Wisconsin breakage tester/rotary blade impactor, respectively. The average fracture force and fracture energy under compression (± one standard deviation) were, respectively, 309.4±107.1 N and 48.7±27.1 mJ for corn, and 83.4±23.8 N and 28.7±13.5 mJ for wheat. The wear damage was insignificant for corn-acrylic, corn-steel, and wheat-acrylic wear tests. For the wheat-steel wear test, the average work done by the friction force to cause pericarp damage was 3.85±1.50 J. A lognormal distribution was used to fit the compression test data, and a three-parameter Weibull distribution was used to fit the repeated impact test data. The statistical models fit the damage probability based on the loading force or input energy with R-squared values over 0.98. It was found that corn and wheat kernels were susceptible to compression and impact loading, while both had high resistance to wear damage. Unlabelled Image • Damage probability models were developed for predicting grain kernel damage. • Corn and wheat kernels were susceptible to impact and compression loading. • Corn and wheat kernels had high resistance to wear damage. [ABSTRACT FROM AUTHOR]

This paper describes an experimental investigation performed to evaluate the low-velocity impact behavior of prepreg-based carbon fiber reinforced polymers (CFRPs) and fiber metal laminates (FMLs) with and without open holes subjected to different impact energies. The laminates were made of carbon fiber/epoxy prepregs and aluminum layers and manufactured by using autoclave. The impact responses of these laminates were experimentally obtained using a drop-weight tower at impact energies of 15, 20 and 30 J. After testing, the impact damage area of tested specimens was quantified from C-scan ultrasonic technique. In addition, an X-ray tomography analysis was performed to assess the through-thickness distribution of damage in FMLs with and without open holes. The results showed that the woven FMLs exhibit the highest impact peak force compared to that of CFRP plates due to the presence of aluminum layers, which induce a higher deformation capability to the laminates. The presence of open holes in laminates tends to augment their damage extension and decreases their impact peak force due to the local stress concentration effect. Nevertheless, it was observed by C-scan ultrasonic images that the aluminum layers reduce the extent of delamination of laminates during the impact event. Postimpact evaluation using X-ray computed tomography showed that impact causes a severe damage to the laminates around their impact point and confirmed that matrix cracking and delamination are the principal damage mechanisms induced on the through-thickness direction of the FML plates. In specific, the results confirm that the aluminum layers provide good impact properties and damage resistance when they are added to the CFRPs. [ABSTRACT FROM AUTHOR]

The present study deals with development of conceptual proof for jute rubber based flexible composite block to completely arrest the projectile impacting the target at high velocity impact of 400 m/s through numerical simulation approach using finite element (FE) method. The proposed flexible composite blocks of repeating jute/rubber/jute (JRJ) units are modelled with varying thickness from 30 mm to 120 mm in increments of 30 mm and impacted by flat (F), ogival (O) and hemispherical (HS) shaped projectiles. All the considered projectiles are impacted with proposed flexible composite blocks of different thicknesses and the penetration behaviour of the projectile in each case is studied. The penetration depth of the projectile in case of partially penetrated cases are considered and the effect of thickness and projectile shape on percentage of penetration depth is statistically analyzed using Taguchi's design of experiments (DOE). Results reveal that the though proposed flexible composite block with thickness of 90 mm is just sufficient to arrest the complete penetration of the projectile, considering the safety issues, it is recommended to use the flexible composite with thickness of 120 mm. The nature of damage caused by the projectile in the flexible composite is also studied. Statistical studies show that thickness of the block plays a prominent role in determining the damage resistance of the flexible composite. [ABSTRACT FROM AUTHOR]

An industrial-scale production and experimental investigation was conducted in order to evaluate the constructability and structural performance of different concrete pipes incorporating discrete synthetic fibers. The results indicated that synthetic fibers enable design of plain concrete pipes with a desired balance of strength and ductility. Analytical models were developed for predicting the load-carrying capacity of concrete pipes without steel reinforcement that are reinforced with discrete fibers. [ABSTRACT FROM AUTHOR]

The investigation of damage development is essential for the design and optimization of hybrid structures. This paper provides a reference for the structural design of brittle-ductile hybrid LVI-resistant laminates through analyzing the damage development mechanism of carbon/Kevlar fabric-reinforced composite laminates. The effects of Kevlar fabric hybrid ply and intercalation on the damage development of carbon/Kevlar composite laminates under low-velocity impact (LVI) were investigated using quasi-static indentation (QSI). It was found that an increase in the Kevlar hybrid ratio significantly reduced the peak load and stiffness of these laminates (the maximum decreases in strength and stiffness were 46.03% and 41.43%, respectively), while laminates with identical hybrid ratios but different plying configurations maintained a comparable stiffness under QSI, with differences of less than 5%. Interestingly, Kevlar fibers exhibited irregular fractures as the yarn was splitting, while carbon fibers presented neat breaks, which indicated material-specific failure modes. Notably, the introduction of Kevlar hybridization beyond pure Kevlar configurations (KKKK) resulted in a decrease in the percentage of fiber damage (CCCC, CCCK, CCKK, and KCCK accounted for 80%, 79.8%, 70%, and 60% of fiber damage, respectively), attributed to an increase in resin cracks and lower levels of Kevlar yarn breakage. The internal damage diameter of specimens was accurately predicted from the diameter of visible damage on the QSI surface. Compared with CCCC and CCKK setups, which are affected by resin cracks formed via the carbon surface on the loading side propagating along the yarn direction (including the yarn settling direction), KCCK demonstrated less delamination between the first and second ply.

Abstract Indoor climate fluctuations are regarded as one of the major risks for the emergence of damage in historical works of art. For a safe preservation of their art objects museums try to minimize this risk, which is typically done by imposing strict limitations on the indoor temperature and humidity conditions. The high energy demand resulting from this approach, however, undermines the aim of preeminent museums to execute a sustainable preservation strategy of their collections. A rational improvement of this aspect asks for detailed information on the history of museum objects, complemented by a thorough comprehension of the failure and deformation behaviour of museum objects under indoor climate fluctuations. Accordingly, in this paper the hygro-mechanical response of mock-ups of historical Dutch cabinet door panels made of oak wood is examined under several relative humidity variations. In specific, the mock-ups were subjected to (i) an instantaneous decrease of 40% relative humidity, (ii) eight successive, instantaneous drops of 5% relative humidity, and (iii) a varying relative humidity profile ranging between 35 and 71%. The shrinkage characteristics of mock-ups are translated to their damage susceptibility using an analytical hygro-mechanical bi-layer model. This model shows that restrained hygral shrinkage may originate from: (i) a difference in moisture content across the thickness direction of the panel, or (ii) a directional difference in the coefficient of hygroscopic expansions of structural components forming a coherent connection. The first type of shrinkage occurs in the outer regions of the panel thickness, while the second type of shrinkage takes place at the cleated ends. Further, by accounting for the age-dependency of the fracture strength of oak wood, a clear distinction can be made between the damage susceptibility of new door panels and historical door panels present in museum cabinets. The six main conclusions of the experimental study—conveniently summarized at the end of this paper—provide a scientific basis for the understanding of shrinkage cracks and dimensional changes observed on decorated oak wooden panels in historical Dutch cabinets, and thus may assist in advising museums on future sustainable preservation strategies and rational guidelines for indoor climate specifications.

Summary: Leaf venation networks evolved along several functional axes, including resource transport, damage resistance, mechanical strength, and construction cost. Because functions may depend on architectural features at different scales, network architecture may vary across spatial scales to satisfy functional tradeoffs.We develop a framework for quantifying network architecture with multiscale statistics describing elongation ratios, circularity ratios, vein density, and minimum spanning tree ratios. We quantify vein networks for leaves of 260 southeast Asian tree species in samples of up to 2 cm2, pairing multiscale statistics with traits representing axes of resource transport, damage resistance, mechanical strength, and cost.We show that these multiscale statistics clearly differentiate species' architecture and delineate a phenotype space that shifts at larger scales; functional linkages vary with scale and are weak, with vein density, minimum spanning tree ratio, and circularity ratio linked to mechanical strength (measured by force to punch) and elongation ratio and circularity ratio linked to damage resistance (measured by tannins); and phylogenetic conservatism of network architecture is low but scale‐dependent.This work provides tools to quantify the function and evolution of venation networks. Future studies including primary and secondary veins may uncover additional insights. [ABSTRACT FROM AUTHOR]

This work relates to the investigation of indentation induced damage resistance in glass fiber reinforced polymer composite laminates under normal and inclined planes. Uni-directional [0] and cross-ply [0/90] glass fiber reinforced polymer composite specimens were subjected to 0° and 20° indentation loading with acoustic emission monitoring. The specimens were loaded at the centre using a hemispherical steel indenter with 12.7 mm diameter. Mechanical responses such as force–displacement behavior, absorbed energy and resulting damage area were used for the quantification of the indentation damage. Acoustic responses such as normalized cumulative counts, energy, duration and peak frequency were considered for monitoring damage progression during 0° and 20° indentation loading. The residual compressive strength of the glass fiber reinforced polymer specimens following indentation was measured by testing them under in-plane loading, once again with acoustic emission monitoring. The correlation between mechanical and acoustic strain energy was used for the evaluation of the damage severity of the laminates. The result revealed indentation damage resistance in cross-ply laminates as 65.08% and 68.01% higher than uni-directional laminates for 0°, whereas for 20°, there was a reduction in the damage resistance in cross-ply laminates to 43.27% and 57.39%. These were higher than uni-directional laminates under the displacements of 2 mm and 3 mm, respectively. The conclusion from these results was that transverse shear load at 20° inclination of laminate leads to reduction in residual compressive strength. Moreover, uni-directional glass/epoxy laminates have better residual compressive strength than cross-ply laminates for both 2 mm and 3 mm indentation displacements. [ABSTRACT FROM AUTHOR]

To avoid certain difficulties in concrete-encased composite construction such as interference between the shaped steel and reinforcing bars and poor concrete placement quality, steel fiberreinforced concrete-encased composite (SFRCEC) section was proposed by replacing the steel reinforcing bars with steel fibers. The bond property between shaped steel and steel fiber-reinforced concrete (SFRC) is crucial to composite members. According to the pushout test of 20 specimens, this paper studies the bond property and interface damage between shaped steel and SFRC. The load-slip curve, bond strength, interface energy dissipation, and other important data are obtained. The differences at the interface from uneven bond force distribution are analyzed. The load and slip are not always the same at different locations along the interface. The influences of embedded length of shaped steel (Le), steel fiber ratio ('sf), and the thickness of concrete cover (Css) are also discussed. For every 100 mm increase in Le, the slip difference between two ends increases by 0.257 mm, which shows a linear growth. When the ratio of steel fiber is between 1 and 3%, the thickness of concrete cover is between 20 and 60 mm, with bigger Css or higher 'sf, and the difference within a unit length becomes smaller. Increasing the 'sf or the Css will enhance the bond and constraint between SFRC and the steel and give higher crack resistance to the concrete cover. This also helps the bond stress distribution along the interface, which means a more balanced loading distribution between two materials at the interface under maximum loading. [ABSTRACT FROM AUTHOR]

[Display omitted] • A novel hybrid/graded ply thickness design strategy was proposed. • The core objective of this paper is how to simultaneously suppress delamination and fiber fracture in laminates. • Laminates with gradient ply thickness exhibit superior load-bearing and damage resistance under short-beam bending. • The hybrid and gradient ply thickness design induces a competition mechanism between delamination and fiber fracture. Ply thickness hybridization is a common strategy in the layup structure of composite laminates. The rational allocation of thin-ply and thick-ply to effectively improve the performance of composite materials is a shared goal. Compared to standard laminates, ultra-thin-ply laminates have many advantages, including design flexibility, better damage tolerance, and enhanced in-situ strength. However, the risk of fiber fracture triggered by ultra-thin-ply requires cautious application. Effectively reducing the risk of fiber fracture caused by ultra-thin-ply laminates has become a challenge in the field of composite materials. Therefore, this paper proposes a thick/thin/thick gradient structure to balance delamination and fiber fracture. Short-beam bending test results demonstrate that this novel gradient structure exhibits good bending load-bearing performance and damage resistance, achieving the coexistence of multiple damage couplings and effectively enhancing damage tolerance. [ABSTRACT FROM AUTHOR]

The main objective of this paper is to investigate damage resistance of Armox 500T and Aluminum 7075-T6 plates subjected to drop-weight and ballistic impact loads. Investigating the behavior of structures under the low or the high velocity impact loads is an important research topic. The study of materials and their combinations provides fundamental understanding of many engineering structures. In this study, firstly drop weight and ballistic impact resistance of the Armox-500T and Al7075-T6 materials was examined. Ballistic impact analyses were carried out using 7.62 API projectiles with an initial velocity of 800 m/s. During the drop-weight analyses, the drop of 5.5 kg weight from the 800 mm distance was modeled. The situations at which target plates of different thickness can be fully penetrated or not to be fully penetrated by the projectile, the final (residual) velocities in the fully penetrated plates and the amount of energy absorbed by the target plates were investigated. 6.72 API projectiles with an initial velocity of 800 m/s could not fully penetrated the 10 mm Armox-500T target and 26 mm Al7075-T6 target. When drop-weight results are concerned, the maximum impact loads of the Armox-500T target is higher than the Al7075-T6, and the deformation amount is less. In addition, 10 different hybrid models, which consist of various combination of Armox 500T and Al7075-T6 materials in different thicknesses and orientations, have been defined. These models were compared with each other and models that are more resistant to ballistic impact loads were determined. M4, M7, M9, and M10 models were found to be more resistant to the ballistic impact loads than other models. [ABSTRACT FROM AUTHOR]

Background and Aims The ability of plants to allocate energy to resistance against herbivores changes with abiotic conditions and thus may vary along geographical clines, with important consequences for plant communities. Seed size is a plant trait potentially influencing plant tolerance to endoparasites, and seed size often varies across latitude. Consequently, plant tolerance to endoparasites may change across geographical clines. Methods The interaction between Quercus ilex (holm oak) and seed-predating Curculio spp. (weevils) was explored along most of the latitudinal range of Q. ilex. This included quantification of variation in seed size, survival likelihood of infested seeds, multi-infestation of acorns and community composition of Curculio weevils in acorns. Key Results Larger seeds had a higher probability of surviving weevil attack (i.e. embryo not predated). Southern populations of oak produced on average four times larger seeds than those of northern populations. Consequently, the probability of survival of infested acorns decreased with latitude. The community composition of Curculio varied, with large weevils (C. elephas) dominating in southern populations and small weevils (C. glandium) dominating in northern populations. However, damage tolerance was robust against this turnover in predator functional traits. Furthermore, we did not detect any change in multi-infestation of acorns along the geographical gradient. Conclusions Quercus ilex tolerance to seed predation by Curculio weevils increases toward the southern end of its distribution. Generally, studies on geographical variation in plant defence against enemies largely ignore seed attributes or they focus on seed physical barriers. Thus, this research suggests another dimension in which geographical trends in plant defences should be considered, i.e. geographical variation in tolerance to seed predators mediated by seed size. [ABSTRACT FROM AUTHOR]

Composite materials employed in engineering services are often subjected to preloads such as pre-tension and pre-compression, necessitating a comprehensive understanding of their effects on the Low Velocity Impact (LVI) damage resistance and tolerance. Driven by this, a Finite Element Analysis (FEA) model, accounting for fibre damage, matrix damage, and delamination, has been developed to capture the LVI behaviors of composite laminates subjected to various preloads. Furthermore, the developed model has also been employed to predict the Compression After Impact (CAI) strength of these composite laminates which have been impacted under pre-loading conditions. By comparing the modelling results with experimental data, the fidelity of the model is demonstrated, especially revealing a deviation of less than 10 % between the measured and predicted CAI strengths. The validated model is then employed to further explore the relationships between LVI behaviors, CAI strength, and different types and magnitudes of preloads under varying impact energies. The findings indicate that a monotonic transition in preloading from compression to tension leads to a reduction in LVI delamination area and energy dissipation, while for CAI strength, it is related with the stacking sequence. [ABSTRACT FROM AUTHOR]

Abstract: The network of minor veins of angiosperm leaves may include loops (reticulation). Variation in network architecture has been hypothesized to have hydraulic and also structural and defensive functions. We measured venation network trait space in eight dimensions for 136 biomass‐dominant angiosperm tree species along a 3,300 m elevation gradient in southeastern Peru. We then examined the relative importance of multiple ecological and evolutionary predictors of reticulation. Variation in minor venation network reticulation was constrained to three axes. These axes described reconnecting vs. branching veins, elongated vs. compact areoles compact vs. elongated and low vs. high‐density veins. Variation in the first two axes was predicted by traits related to mechanical strength and secondary compounds, and in the third axis by site temperature. Synthesis. Defensive and structural factors primarily explain variation in multiple axes of reticulation, with a smaller role for climate‐linked factors. These results suggest that venation network reticulation may be determined more by species interactions than by hydraulic functions. [ABSTRACT FROM AUTHOR]

Abstract: Zirconium diboride with 20 vol.% silicon carbide bulk composites were fabricated using directionally solidification (DS) and also by spark plasma sintering (SPS) of crushed DS ingots. During the DS the cooling front aligned the c‐axis of ZrB2 grains and its Lotgering factor of f(00l) was high as 0.98. The Vickers hardness was anisotropic and it was high as 17.6 GPa along the c‐axis and 15.3 GPa when measured in an orthogonal direction. On both surfaces, even when using 100 N indentation load, no cracks were observed, suggesting a very high resistance to crack propagation. Such anomalous behavior was attributed to the hierarchical structure of DS sample where the ZrB2 phase was under strong compression and the SiC phase was in tension. In the SPSed sample, the microstructure was isotropic respect to the direction of applied pressure. Indentation cracks appeared around the indent corners but not emanated from the diagonals, confirming high damage resistance. [ABSTRACT FROM AUTHOR]

[Display omitted] • Crack driving force for hole-like features was determined as a function of their size and volume fraction. • Blunting effect of holes is quantified using finite element modelling. • Effect of a single hole feature as well as full architectures on fracture resistance has been experimentally determined. • Counterintuitively, increasing the number of layers containing hole features eliminates catastrophic failure and enhances fracture resistance. • An increase in the size of holes leads to an increase in the overall fracture resistance of the structure. This study investigates the effect of feature size, volume fraction, and sample size on the damage resistance of an architected brittle Poly(methylmethacrylate) (PMMA) polymer. Holes with varying diameters and number of layers were micro-machined in samples of different sizes in PMMA throughout the beam and tested under bending in the presence of a pre-crack. The initiation and total work of fracture (WOF) are determined for different feature sizes of holes. In the case of a single hole feature ahead of the crack tip, overall fracture resistance increased with increasing diameter of the hole, while no effect was seen on the initiation fracture resistance. This was reflected as increased damage resistance in the fully architected specimen with increasing diameter of holes as well as with increasing number of layers of the features (and hence their volume fraction). However, an increase in sample size led to catastrophic failure and a decrease in damage resistance. These effects are quantifiably explained in terms of crack driving force calculations done through finite element modelling. [ABSTRACT FROM AUTHOR]

• A hybrid damage model was proposed to predict cryogenic deformation damage of FSW blanks. • Experimental and predicted results indicated that the joints properties, forming limits and LDR were improved at cryogenic temperature. • The improvement in the formability of FSW blanks was attributed to the slower damage accumulation and enhanced voids damage resistance at cryogenic temperature. The cryogenic deformation damage and formability of AA2219 FSW blanks were systematically studied with a novel hybrid damage model. The model combined the meso-GTN model and modified Mohr‒Coulomb ductile fracture model considering the complex stress states. The damage parameters of the weld and BM zone were obtained by the finite element reverse calibration method. The tensile properties, forming limits and deep drawability of the FSW blanks were analyzed with calibrated damage model. The damage differences and accumulation rate of the weld and BM zone both decreased, and the deformation uniformity of the FSW joints was improved at −196 °C. In addition, the proposed model can accurately predict the damage and cracking of FSW blanks under uniaxial tension, plane strain and biaxial tension. The maximum standard deviation of the major strain is only 11.7%. The global damage behavior of the weld zone was analyzed during cryogenic deep drawing of the hemispherical bottom cylindrical part. The predicted fracture position and direction of the simulations were in good agreement with those of the experiments, and the LDR increased to 1.9 at −196 °C. The improved formability of the deep drawn parts was mainly due to the increased damage resistance of the weld zone. The decreased voids coalescence rate and dense slip bands were all conducive to the improvement of damage resistance. [Display omitted] [ABSTRACT FROM AUTHOR]

We employ instrumented nanoindentation for obtaining quantitative information on the onset of scratch-induced microabrasion on silica glass. For this, in situ evaluation of lateral force and friction coefficient is compared to post mortem optical inspection, following edge-forward scratching with a Berkovich indenter at velocities of 10–500 μm/s under continuously increasing normal load of up to 300 mN. In the two approaches, the onset of microabrasion is identified from the occurrence of pop-ins in the load-displacement curve and phenomenologically determined from the scratch pattern, respectively. Obtained data are analyzed in terms of a Weibull distribution, assuming that microabrasion sets-on as a result of acting stress as well as surface state. Aside of the occurrence of occasional outliers at low load (probably induced through individual surface defects), data indicate two underlying probability functions, i.e. , the probability for the propagating scratch to hit a surface flaw and the probability that such an event causes an observable micro-crack. Dominance of the former leads to an exponential function with Weibull modulus ~ 1, reflecting a purely random distribution with load-independent probability of failure. This is observed in particular at high scratching velocity after passing a certain normal load. For the latter, the Weibull modulus increases with increasing scratching velocity, that is, from ~ 1.6 to 4.4, at intermediate load. Here, low Weibull modulus at low load is attributed to the increasing time of local strain, which leads to a reduction of the load-dependence of micro-cracking relative to a faster-moving scratch. In the present case, the critical lateral load for microabrasion of silica (50th percentile) is around 30–40 mN. Within the employed experimental conditions, this value is practically independent of scratching velocity. [ABSTRACT FROM AUTHOR]

Sodium aluminoborate glasses are found to exhibit favorable mechanical properties, especially high crack resistance, due to their relatively low resistance to network compaction during sharp-contact loading. We here reveal the origin of the high crack resistance by investigating changes in structure and mechanical properties in compositions ranging from peralkaline to peraluminous and by varying the pressure history through an isostatic N 2 -mediated pressure treatment at elevated temperature. This approach allows us to study the composition dependence of the ease of the glassy network compaction and the accompanying changes in structure and properties, which shed light on the processes occurring during indentation. Through solid state NMR measurements, we show that the network densification involves an increase in the average coordination number of both boron and aluminum and a shortening of the sodium-oxygen bond length. These changes in the short-range order of the glassy networks manifest themselves as an increase in, e.g., density and indentation hardness. We also demonstrate that the glasses most prone to network compaction exhibit the highest damage resistance, but surprisingly the crack resistance scales better with the relative density increase achieved by the hot compression treatment rather than with the extent of densification induced by indentation. This suggests that tuning the network structure may lead to the development of more damage resistant glasses, thus addressing the main drawback of this class of materials. [ABSTRACT FROM AUTHOR]

This paper focuses on the experimental investigation of impact damage resistance in hybrid composite laminates. In this case, the low velocity impact behaviour of quasi-isotropic glass/epoxy, glass/basalt/epoxy (G/B/G, B/G/B) and glass/carbon/epoxy (G/C/G, C/G/C) composite laminates was simulated by carrying out quasi-static indentation (QSI) tests with online acoustic emission (AE) monitoring. The dent depth, back surface crack size and load-deflection behaviors were examined and there is no distinct differences could be seen between low velocity impact tests and quasi-static indentation tests. The QSI tests were performed on specimens with rectangular section, of size 150 mm x 100 mm, which were loaded at the centre by a hemispherical steel indenter with 12.7 mm diameter. The indentation response was evaluated by measuring peak force, absorbed energy and linear stiffness. The residual strength of the laminates following indentation was measured by testing them under compression load in a 100 kN universal testing machine, once again with AE monitoring. AE parameters, such as amplitude, rise time, cumulative counts and cumulative energy were considered for monitoring damage progression during quasi-static indentation loading. Also other parameters linked to AE monitoring, such as the rise angle (RA) and Felicity ratio (FR) were measured for evaluating the damage resistance in each cycle of indentation. In addition, sentry function was also computed based on the combination of mechanical strain energy accumulated in the materials and of the acoustic energy propagates by fracture events made it possible to evaluate the amount of induced damage. These results showed that the combination of glass and carbon fibres in glass/carbon/epoxy (C/G/C) laminates improved their interlaminar shear strength at a level well above the other configurations tested. [ABSTRACT FROM AUTHOR]

Underground facilities used for a wide range of civil and military applications such as transportation, storage, and water and sewage conveyance etc. to name a few. These structures can get damaged by the constant overburden loads and litho-static pressure of high rise buildings and apartments. Load - deformation assessment of these tunnels is important in designing damage resistant strategic as well as civilian structures. The fracture behaviour and the damage resistance of the geologic materials under severe loading conditions depend on various factors such as strength, density, static and dynamic response. Due to heavy loading, structures experience high strain-rate and there is an apparent increase of the dynamic strength when geo-materials such as soft and weathered rock / synthetic rock are subjected to high strain-rate. From a practical point of view, when designing underground excavations in rocks, the goal is to minimize stress concentration problems, create a stress field as uniformly distributed as possible in the excavation of underground structures so that the optimum support systems is provided without compromising the safety of the structure. Therefore, the strength augmentation of geo-materials has drawn enormous concern in structural design under different loading condition. [ABSTRACT FROM AUTHOR]