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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]

The essential work of fracture (EWF) method was used to assess the in-plane toughness of a paper containing poly(ethylene terephthalate) (PET) and cellulose fibers before and after ultraviolet (UV) aging. It was found that this paper meets the basic requirements of the EWF method, at least in the yielding/blunting-related stage. The related EWF terms decreased with increasing UV aging. A similar trend was observed for the tensile mechanical parameters. Fractographic inspection showed that UV aging resulted in improved wetting of the PET fibers by the binder used. Instead of its beneficial effect, however, an adverse trend was found. This was traced to the UV-caused “embrittlement” of the cellulose fibers, which hampered the deformability of the web composed of PET and cellulose fibers. [ABSTRACT FROM AUTHOR]

In this paper, dynamically propagating cracks in anisotropic plates exposed to a generalised thermal shock are investigated. Here, the governing equations are considered according to the Lord-Shulman (LS) model as a fully coupled generalised thermoelasticity theory. The crack is modelled in the context of the eXtended Finite Element Method (XFEM). To evaluate Stress Intensity Factors (SIFs), a technique based on the J integral and crack tip opening and sliding displacements, previously applied for stationary cracks, is developed for a dynamically propagating crack in orthotropic solids. Besides, a variety of functions for enriching the displacement field are derived relying on the behaviour near the tip of a dynamically propagating crack in anisotropic materials. The maximum hoop stress criterion is also modified by using the asymptotic stress field for a dynamically propagating crack. In addition, the effect of the angular variation of fracture toughness in orthotropic materials is accounted in computing the crack propagation speed. In some examples, dynamic crack growth in complex cracked orthotropic structures subjected to LS thermal shock is studied in detail. The impacts of fibre orientations and LS relaxation time are also investigated in these examples. In conclusion, applying non-Fourier thermal shock for modelling dynamically propagating cracks in orthotropic structures is recommended to obtain more realistic results. In addition, by increasing the LS relaxation time, the crack grows less oscillatory and is more aligned along the material fibres. [ABSTRACT FROM AUTHOR]

In this paper, the distributed dislocation technique (DDT) is used to calculate the stress intensity factors (SIFs) at the tip of several moving cracks which are located at the interface between two dissimilar non-homogeneous half-planes. In this study, in-plane loading is considered and it is assumed that the properties of the non-homogeneous material change exponentially. First, by employing Fourier and Galilean transforms, the problem of Volterra type climb and glide edge dislocation is solved at the interface of two dissimilar materials, and then the DDT is used to obtain the singular integral equations of Cauchy type. The resulting singular equations are numerically discretized and solved to obtain dislocation density on the crack surfaces to determine the SIFs. Finally, the effects of change in parameters such as gradient non-homogeneous constant, Poisson ratio, crack growth rate and interaction between cracks on SIFs are shown graphically. [ABSTRACT FROM AUTHOR]

This paper presents assessments performed on a large database of virgin material and irradiated material thermal creep data from uniaxial and pressurised DIN 1.4970 Ti-stabilised austenitic stainless steel i.e. EN X10NiCrMoTiB15–15 or '15-15Ti' cladding tubes. The data base incorporates multi-heat data from uniaxial and bi-axial (internal pressure) creep tests conducted during the fast reactor R&D program of the DeBeNe (Deutschland-Belgium-Netherlands) consortium between the 1960s to the late 1980s together with more recent data, for example, from the European projects MATTER and PATRICIA and the EERA JPNM pilot project TASTE. The data comprises of a virgin material data base and a data base with irradiated creep data. The virgin material data comprises of time-to-rupture and time-to-0.2% creep strain in a temperature range of 600–800°C and covers a large range of stresses. The irradiated data base has less data and does not cover all material heats tested for the virgin material properties. The irradiation conditions are also different depending on the test reactor specifics and the irradiation campaign targets. The attained 'irradiation damage' in displacements per atom (DPA) for the irradiated materials range from 0.1 up to 38.1. Un-irradiated 'reference material' models for tensile strength and creep strength are constructed from the current-state of the art literature data and more recent results from the Sandvik 24% cold worked 1515–Ti cladding tube currently used as the main material batch studied at SCK CEN. The tensile strength model is used throughout the paper for normalizing creep strengths by the tensile properties, needed when applying the Wilshire (WE) creep model. Time factors (TF), stress factors (SF) and temperature ratio factors (TRF) are calculated for different material states for describing the impact of heat treatments, (virgin and irradiated) and irradiation conditions. This initial study targets to give estimates for the thermal creep properties of cladding tubes with a cold work range of 16–24% in a non-annealed state, as it is the preferred option for future designs according to the state-of-the art knowledge base. However, the main bulk of the available data on irradiated material is on claddings with a cold work range of 0-16% with and without annealing and at various levels of irradiation damage, thus leading to the need for estimation by interpolation and extrapolation assuming that irradiation damage levels and trends, e.g. time reduction factors found on a lower cold worked material can also be applied on materials with higher cold work levels. The results of the assessments clearly show relative strength differences between chosen material heats and heat treatments and has enabled constructing simple multilinear models for estimating the life of irradiated material. The models show that low creep test temperatures (and irradiation temperatures), low stress levels, low levels of cold work and high irradiation doses are increasing the detrimental difference between the specific material condition and the reference material. Also, it was found that the general level of life reduction (time factor TF and stress factor SF) for irradiation damaged material failure, in relation to the reference material failure, roughly coincides the corresponding values of time to 0.2% creep strain for virgin material. The estimated 'failure creep temperature limits' for 30 000 hours of service are studied and compared for both virgin and irradiated materials at a reference stress level of 1/3 of the tensile strength (at temperature). [ABSTRACT FROM AUTHOR]

Abstract–The Weibull distribution is the most applied model in reliability field for lifetime analysis. The Weibull location parameter, characterizing the minimum possible life, plays a significant role in engineering applications. In this paper, we consider the interval estimation on the location parameter when the product's lifetime follows the three-parameter Weibull distribution with a known shape parameter. A novel approach based on the relationship between the minimum order statistics, the location parameter, and the sample size is developed to construct confidence intervals for the Weibull location parameter. Thereafter, we compare it with other two interval estimation approaches by the performances of the coverage probability and the average length via simulations and a real application. The results show that the proposed method outperforms the pivot quantity (PQ) method and the bias-corrected and accelerated (Bca) bootstrap method in small and medium samples in terms of coverage probability. [ABSTRACT FROM AUTHOR]

This document is a summary of a special issue of the journal "Mechanics of Advanced Materials & Structures" titled "Recent Advances in Nonlinear Structural Mechanics and Failure Analysis." The special issue is a collection of selected papers presented at the first International Conference on Advanced Topics in Mechanics of Materials, Structures, and Construction (AToMech1) held in Saudi Arabia in March 2023. The conference aimed to foster sustainable development and facilitate international networking among researchers, practitioners, and educators in the fields of mechanics of materials, structures, and construction. The special issue covers various topics such as advanced structural models, damage and fracture mechanics, metamaterials and acoustics, large deformation analysis, peridynamic theory, multi-physics and coupled problems, and advanced materials and structures. The papers in the special issue explore innovative approaches and solutions in these areas. The special issue is internationally significant and was made possible through the collaboration of the journal, the conference organizing committee, and the guest editors from different countries. The summary expresses gratitude to all those involved in making the special issue possible. [Extracted from the article]

In the framework of the Cost Action CERTBOND (Reliable roadmap for certification of bonded primary structures), a wide group of researchers from 27 European Countries have had the opportunity to work on the topic of certification of bonded joints for primary structural applications from different engineering sectors such as the aerospace, automotive, civil engineering, wind energy and marine sectors. Since virtual testing and optimization are basic tools in the certification process, one of the key objectives of CERTBOND is to critically review some of the available models and failure theories for adhesive joints. The present paper summarizes the outcome of this task. Nine different models/theories are described in detail. Specifically, reviewed are the Classical Analytical Methods, the Process Zone Methods, Linear Elastic Fracture Mechanics (LEFM), the Virtual Crack Closure Technique (VCCT), the Stress Singularity Approach, Finite Fracture Mechanics (FFM), the Cohesive Zone Method (CZM), the Progressive Damage Modeling method and the Probabilistic methods. Also, at the end of the paper, the modeling of temperature effects on adhesive joints have been addressed. For each model/theory, information on the methodology, the required input, the main results, the advantages and disadvantages and the applications are given. [ABSTRACT FROM AUTHOR]

The main objective of this paper is to investigate the bearing capacity behaviour of cracked plates considering low-cycle fatigue (LCF) propagation under cyclic loads. The accumulative plastic damage after crack growth is treated as the residual stress and deformation of the plate. In this study, a cracked plate model is proposed to investigate the difference of its residual ultimate strength with preset crack and LCF crack. The present study has analysed the relationship between accumulated lateral deflection and residual stress of cracked plates in different cases. Its effect on the collapse behaviour of the cracked plate is also discussed. The influence factors such as crack length, tensile /compressive cyclic loads, maximum load, minimum load and crack location type are considered in the ultimate strength study of cracked plates. The numerical results clearly reveal the accumulative plastic damage and the bearing capacity behaviour of cracked plates under different cyclic loads. [ABSTRACT FROM AUTHOR]

Continuum damage mechanics (CDM) studies the deterioration of mechanical properties in materials that leads to material failure. The Lemaitre's ductile damage model is known as a suitable criterion for damage growth in ductile materials. The standard Lemaitre's model cannot accurately predict the damage growth in most of bulk metal forming processes with a combination of tension and compression loadings. In this paper, first, an explicit step-by-step algorithm of the Lemaitre's ductile damage model conjugated with the crack closure effect in compressive loadings is provided and directly presented for the computational implementations. Then, employing the proposed algorithm, a user-defined material subroutine is developed and implemented. In the following, a few bulk metal forming processes under compressive loadings are numerically simulated. Finally, the numerical simulation results are compared with the prediction results of the standard model and also experimental tests. The comparison confirms the high precision of the modified model vs. the standard model. Hence, it is concluded that the modified Lemaitre's model can truly predict the damage behavior of ductile materials in bulk metal forming processes with combined tensile and compressive loadings. [ABSTRACT FROM AUTHOR]

Elastomeric materials are often used as components that undergo cyclic loading during application, such as tires, seals, and hoses. For this reason, the long-term performance, or more precisely the crack growth behavior, is of great importance. Even though several studies investigated the fatigue behavior of rubber materials during the last 80 years, this topic is still widely under discussion and remains of great interest among scientists. Mars and Fatemi reviewed the developments of the field in the beginning of 2000, however, this paper considers the overall development including new findings to serve as a guide for further investigations in the field of fatigue of elastomers. For this purpose, the usual measurement methods and their evaluation, as well as the most important factors influencing the fatigue behavior, like the formulation of the rubber compound or the application and testing conditions, are explained in detail. Furthermore, an outlook is given on parameters that still need to be scientifically investigated, such as the influence of filler orientations or the selected manufacturing method, in order to fully understand fatigue crack growth. [ABSTRACT FROM AUTHOR]

Composite sandwich panels are commonly considered as lightweight materials for structural design in many applications including automotive, aerospace and defence systems. These panels must be developed and validated for its mechanical strength characteristics under different loading conditions before deploying them for the practical application. Hence, the present paper deals with the experimental and numerical studies on composite sandwich panels subjected to quasi-static edgewise and flatwise compression loads. The composite face sheet was developed using 2 × 2 bi-directional 200GSM twill carbon fibre with hot cure benzoxazine resin. Sandwich panels were made using the developed composite face sheets with aluminium honeycomb core. The developed composite face sheets were tested for tensile and flexural conditions and the sandwich panels for edgewise and flatwise compression loads. Three samples for each of these tests were conducted in Shimadzu UTM with 50 kN capacity machine. A consistent load-displacement profile and the failure pattern were observed for all the samples tested in each test category. It is noted from these tests that the composite face sheets exhibited an ultimate tensile strength of 444 MPa and a flexural strength of 842 MPa which is pretty to close to the epoxy based composites used in the aerospace applications; sandwich panels showed an edgewise compressive strength of 610 MPa and flatwise compressive strength of 3.5 MPa. Tensile test coupons initially had undergone certain delamination before failure and failed close to the specimen holding end. Flexural test specimens were shown delamination of only one layer at the loading face. However, the specimen was well intact together even after failure. Bending mode of failure was noted during edgewise compression test of the sandwich; severe delamination was seen in the tension side of the sandwich whereas a line-folding crack with failure was exhibited at the mid-plane of the specimen. In case of flatwise compression, no evident of damage was observed in the sandwich structure. The second part of the paper describes the numerical simulations of these test cases including tensile, flexural, edgewise compression and flatwise compression using an explicit finite element solver viz. LS-DYNA. Material type 22 and 26 was selected to define the material behaviour of composites and honeycomb respectively. The delamination was modelled using *CONTACT_AUTOMATIC_SURFACE_SURFACE_TIEBREAK card with option 9 that works under B-K linear fracture mechanics law to define the normal and shear failure of cracks. The numerical results were found to match well with experimental observations for the individual coupons as well as the sandwich samples. Therefore, it is concluded from this study that the developed LS-DYNA simulation methodology can be used as a tool for composite sandwich panels based lightweight structural design. [ABSTRACT FROM AUTHOR]

This paper presents a numerical framework for implementation of cohesive zone model with smoothed floating node method (SFNM) for failure analysis of quasi-brittle materials. The nonlinear behavior of material inside the fracture process zone in front of the crack tip is modeled with a potential-based intrinsic cohesive zone approach. Here, SFNM is used to represent the kinematics of crack and the crack front inside the domain without the requirement of remeshing and discontinuous enrichment functions during crack growth, hence resolves the issues associated with the existing discrete numerical methods. A strain smoothing technique is adopted over the domain through which classical domain integration changes to line integration along each boundary of the smoothing cell, hence derivative of shape functions are not required in the computation of the field gradients, thus resolves the issue of element distortion. The proposed numerical framework is firstly verified using the patch test of the two-dimensional specimen under mode I and mode II loading conditions and subsequently extended for solving the two-dimensional standard fracture problems. The effectiveness of the proposed framework is checked by comparing the computational results with the available literature results. [ABSTRACT FROM AUTHOR]

In this paper, a novel dual architecture phase lattice (DPL) structure consisting with hard and soft phases is proposed, and their mechanical properties as well as the deformation features under compression are investigated. Firstly, two different types of basic cubic cells are selected as the constitution phases, and the DPLs with different arrangements are then constructed by additive manufacturing. Quasi-static compression tests and numerical simulations are performed to explore the deformation patterns and stress-strain responses. The compressive strength, plateau stress and the specific energy absorption of the DPLs are characterized. The effects of base material fracture, rod diameter and the cell arrangements on the mechanical responses are explored. Results show that the deformation and failure initiate in the matrix phase and trigger the embedding of the reinforcing phase into the crushed regions. The fracture of the rods results in a lower stress level and more serious fluctuations in the stress-strain responses. Increasing the rod diameter is an effective approach for enhancing the compressive strength and specific energy absorption. Introducing appropriate agreements of reinforcement phases can result in 112% and 37% increments for the compression strength and specific energy absorption, respectively. The findings of this work can facilitate the designs of lattice structures with outstanding mechanical properties and energy absorption performances. [ABSTRACT FROM AUTHOR]

The univariate Birnbaum-Saunders distribution is quite useful for modeling lifetime data, reliability problems, and times to failure for materials subject to fatigue. On the other hand, multivariate extensions of this univariate distribution are not common in the statistic literature. In this paper, based on the multivariate power-normal distribution and univariate Birnbaum-Saunders power-normal distribution, we extended the univariate Birnbaum-Saunders distribution to the multivariate setup. Structural properties of the new multivariate Birnbaum-Saunders distribution are established. We consider the maximum likelihood method to estimate the unknown parameters, as well as the two-stage estimation procedure, which is defined for multivariate copula-based models. Monte Carlo simulation experiments are carried out to investigate the performance of these estimation methods. An empirical application of the proposed multivariate distribution to real data is provided for illustrative purposes. [ABSTRACT FROM AUTHOR]

This paper presents the numerical and experimental results of the mechanical and microstructural properties of liquefied petroleum gas cylinders from local sources. The tensile strength, burst and fracture toughness of the materials were also investigated. The results show that the carbon content for all samples averaged ~0.22 wt% and manganese ~0.76 wt% and the microstructure was largely pearlitic. The tensile strength showed that LPG-C3 recorded high tensile strength of ~ 611 MPa and hardness of ~ 200 HV while LPG-C5 recorded low tensile strength of ~ 450 MPa. The finite element analysis (FEA) showed fracture toughness of ~5 × 105 MPa.mm0.5 for LPG-C2 and the energy release rate of ~2 × 106J/m² for LPG-C5. All samples exhibited high resilience to crack propagation which showed ductile fracture after tensile test. The implications of the results are discussed to elaborate on the influence of carefully controlling the alloying elements of LPG cylinder materials on their mechanical and microstructures during fabrication. [ABSTRACT FROM AUTHOR]

The paper presents a critical analysis of the procedures for defect propagation assessment recommended by British standards and their application to rotating components. The way of applying these procedures was shown by an example of a steam turbine rotor with particular use of a characteristic strain model of high-temperature creep. Calculations of the flaws located at the rotor axis have shown that their growth in the design life is small. The performed analyses have also shown that crack development due to low-cycle fatigue is comparable to that due to creep and cannot be ignored under typical service condition. It was also shown that there is no risk of brittle fracture in the rotor under typical start-up conditions. The presented results prove the usefulness of the methods included in the British standards and guidelines for crack growth assessment in components subject to centrifugal load. [ABSTRACT FROM AUTHOR]

Acoustic Emission (AE) is sensitive to micro-mechanisms of deformation and fracture processes and can give indication prior to failure of a material. The parameters of the AE burst signals are correlated to the micro mechanics of damage and hence desired to be extracted in real-time. This paper proposes a hardware-based approach for extraction of AE signal parameters such as peak amplitude, RMS, AE count, event duration, and rise time, which reduces processing load of the microcontroller and signal processing time significantly. Multisim software is used for simulation of the hardware design and the results are presented in this paper. [ABSTRACT FROM AUTHOR]

In this paper, a numerical simulation method based on the camshaft casting process and crack expansion was proposed to study the propagation characteristics of casting hot cracks. The dynamic visualisation process of hot crack growth indicates that the formation of hot tear is dominated by opening mode cracks. And during the propagation process, the equivalent stress intensity factor at the crack front first decreases and then increases. Furthermore, the propagation characteristics of the crack under different hot tear initiation conditions were studied by this method. The results reveal that the expansion ability of a hot crack is affected by the equilibrium solidification scale, solidification sequence, and solidification path of the casting. Finally, using the microscopic morphology of the cracks, the semi-quantitative analysis of the elements illustrates that the carbon content decreases sharply at the crack formation site, while manganese and sulphur are relatively rich. [ABSTRACT FROM AUTHOR]

Joule heat induced by electric current may well lead to thermal stress and contribute to structural failure and crack evolution in a range of modern materials. In this paper, we use complex variable methods to obtain the thermoelastic fields around an elliptic cavity in a plate subjected to remote electric and thermal loads. Of particular interest is the fact that we consider the temperature dependency of the corresponding thermoelastic coefficients. We introduce an analytical method which is verified by the fact that it leads to results which reduce to the classical analytical results in the literature when the thermoelastic coefficients are taken to be temperature-independent. We find that when the elliptic cavity is reduced to the representation of a linear crack, the corresponding stress intensity factor increases to a greater extent under the temperature-dependent assumption versus the corresponding classical results. Our findings are significant in forming the basis for the analysis of the evolution of crack growth under severe temperature gradients such as those occurring as a result of Joule heat loading. [ABSTRACT FROM AUTHOR]

In this paper, we implement the combined method of drilling stop hole and FRP reinforcement to repair cracked steel plates subjected to cyclic tension. The crack initiation and growth are experimentally investigated. The stress distribution at the stop hole and the residual fatigue life are evaluated by the FEM. The effects on prolonging residual fatigue life are analyzed. The results show that the effectiveness of only using the stop hole is limited, while the combined method has dramatically prolonged the residual fatigue life. The effect mainly owes to the increasing of the crack initiation life from the stop hole. [ABSTRACT FROM AUTHOR]

It is observed that the dwell-fatigue cracks grow faster than the fatigue cracks for the titanium alloys. The dwell-fatigue behaviours have a great influence on the accurate life prediction of submersible pressure hulls. A modified model is proposed to predict the dwell-fatigue crack growth behaviour of titanium alloys under different dwell times and ratios in this paper. Based on the predicted model advanced in the authors' group, the crack tip plastic zone is modified by introducing the crack tip plastic induced by the dwell time in the modified model. The parameters of the crack tip plastic zone induced by the dwell time are determined by the room temperature creep tests. The fatigue and dwell fatigue crack growth rate of the two titanium alloys under different stress ratios and different dwell times are predicted successfully by the modified model. The model is validated by comparing model prediction results with the experimental data. [ABSTRACT FROM AUTHOR]

Sandstone is a common sedimentary rock that is easily carved due to its weakly cemented fine grains and relatively low strength. Therefore, numerous large-scale grottoes in China are made of sandstone. However, these sandstone cultural heritage structures are often seriously damaged due to temperature and humidity changes, air pollution, biodeterioration, and repeated dissolution and crystallization of soluble salts. In general, it is imperative that a consolidant capable of providing cohesion by infilling pores between the stone grains is synthesized. In recent years, it has been reported that using organic consolidation materials for sandstone protection comes with various negative effects, such as a short lifetime, poor compatibility, and preservation damage. Using inorganic consolidation materials to protect sandstone seems to be one of the research trends for the future. Herein, this paper introduces a permeable, inorganic magnesium-based material (MMH solution) for silica sand consolidation. To assess this consolidant, the paper investigates the influence of varying molar ratios of MgO:MgCl2·6H2O:H2O on properties such as penetration depth, consolidation weight, colour variation, and compressive strength. The results demonstrate that the molar ratios of MgO:MgCl2·6H2O:H2O can significantly affect the consolidation performance. Additionally, it is believed that the MMH solution of MgO:MgCl2·6H2O:H2O = 5:1:16 can be successfully used for the consolidation of silica sand, as the cubic specimens' surface micrographs show good compatibility between the consolidation product and sand grains. Experiments (i.e. weight loss rate and mineralogical compositions analysis) are performed to evaluate the cubic specimens' water resistance properties after being immersed in water. Furthermore, the consolidation material's failure mechanism as a self-sacrificing material is preliminarily analyzed. Results indicate that MMH solution is a promising conservation material that shows great potential for consolidating severely weathered sandstone. [ABSTRACT FROM AUTHOR]

Novel methods to probe and evaluate the mechanical properties of High entropy alloy are gaining popularity to accelerate the development of new material for structural application and for establishing the physics-based mechanical property models. Nanoindentation techniques are predominantly suitable for evaluating the properties of materials in which deformation volumes can be cautiously controlled, and indentation can be applied to probe the properties of specific phases or features present within the microstructure. The current investigation is based on the plastic deformation response of Eutectic High Entropy Alloy, AlCoCrFeNi2.1, using experimental and computational approaches. In this paper, the plastic deformation of eutectic high entropy alloy AlCoCrFeNi2.1 is investigated using nanoindentation over a broad range of strain rates at room temperature to probe the mechanical properties of Eutectic High Entropy Alloy, AlCoCrFeNi2.1 and also to understand its elasto-plastic behaviour of BCC and FCC phase present in the alloy. In order to capture the deformation mechanism of material under the tip of the nano-indenter as well as to predict the load variation with depth, molecular dynamic simulation is performed. A characteristic load-depth curve has also been generated from the developed model, which is in good agreement with the experimental one. These findings will lead to understanding the phase-specific contribution to bulk mechanical response of multicomponent alloys and aid in designing structural materials with high fracture toughness. [ABSTRACT FROM AUTHOR]

The use of the composite pultruded materials is increasing due to the particular characteristics of lightness, ease of installation, high corrosion resistance and, finally, lower maintenance costs. Even if the bolting technique is the most widely used, especially in the field of civil engineering re-adapting the rules valid for steel structures, thanks to several studies on adhesives, there is reason to believe that the best connection technique for pultruded profiles is gluing (the continuity of the fibers is guaranteed). Current applications involving such materials, strictly related to the field of civil engineering, include bridges, pedestrian and the motorway bridges, roof structures, helipads, solar charging stations, offshore structures, cooling towers and lockgates. In some of these structures, the system (composite material and resin) is in contact with water. Even if there are several studies on the durability of composite pultruded material, current literature referring to adhesives between pultruded adherents needs further investigation. Within this framework, the paper aims to investigate, from an experimental and numerical point of view, the effect of the hygrothermal ageing on both the fracture energy in mode II as well as the strength and stiffness of two commercial epoxy resins taking into account the further effect of the desorption. Finally, in view of a safe design of a bonded joint, limiting its behaviour to the elastic field only, a lower fracture energy value is presented in relation to the classical one. [ABSTRACT FROM AUTHOR]

Polysilazane-based ceramic coatings have ever-increasing applications in critical and high-power engineering. This paper analyzes the effects of the substrate grain size, the curvature of the coating-substrate interface and the pore-free coating layer on the plastic strain localization and fracture of the porous ceramic coating–polycrystalline substrate structures under compressive loading applied to the coated surface. Models for generating pore and polycrystalline structures of the coating and substrate are developed, with the experimentally observed microstructures of the coated steel being taken into account in calculations explicitly as the initial data of the boundary-value problem. Numerical results obtained by the finite-difference method show that the crack-initiation strain depends on the substrate grain size exponentially. A comparison between the models with serrated and plane coating-substrate interfaces suggests that in the former case, coating cracking initiates near the humps of the interface concavities and the top and bottom pore surfaces, while in the latter case, two sites of cracking nucleation can be distinguished, namely, close to the pores – in the fine-grained substrate, and near the coating-substrate interface – in the case of coarse grains. The results indicate that it is preferable to use the coated specimens characterized by a serrated coating-substrate interface. [ABSTRACT FROM AUTHOR]

Shape memory alloys (SMAs) are able to recover large inelastic strains due to their thermal-/stress-induced phase transformation between austenite and martensite. Stress raisers can either initially exist in SMA components as the manufacturing-induced micro-defects, or may nucleate upon monotonic/cyclic loading, for instance, due to decohesion of the second particles or local cyclic plastic deformations. Furthermore, from a physical point of view, there is a problem why SMAs can withstand tens of millions of cycles if they deform elastically but only thousands of cycles if the martensitic transformation is involved in their cyclic deformation under the stress, even if the martensitic transformation is reversible. One of the possibilities is the nucleation and propagation of cracks from the stress raisers since the evolution of the transformation and local mechanical gradients are completely different at the high-stress zones at stress raisers than that being experienced within the elastic bulk. Thus, the successful implementation of SMA elements into engineering applications requires understanding and analysis of the role of the stress raisers in fracture and fatigue crack growth properties of shape memory alloys. The linear and non-linear Fracture Mechanics theories, commonly used to describe the fracture processes in typical structural alloys, need to be enhanced to capture the complex deformation mechanisms characterizing SMAs. In the present paper, first, the latest progress made in experimental, numerical, and theoretical analyses on the role of the stress raisers in the fracture parameters of SMAs are reviewed and discussed under both pure mechanical and thermomechanical loading conditions. Then, the state-of-arts in fatigue crack growth are addressed. In the end, summary and future topics are outlined. [ABSTRACT FROM AUTHOR]

In the CCG life assessment for defective structures based on the two-parameter method with considering constraints, the establishment of a correlation equation between the constraint parameter and the CCG rate for a material at a temperature is very important, but it is difficult and costly. For engineering applications, it is desirable to have a unified correlation equation for different materials. In this work, based on a large amount of experimental CCG rate data of different specimens from the literature, combining with the finite element (FE) calculations of a new unified creep constraint parameter Ac ,, a unified correlation equation has been obtained. In the CCG life evaluation for cracked structures based on the C*-Ac two-parameter method, this correlation equation may be used to estimate the constraint-dependent CCG rates for any materials at different temperatures. The correlation equations of eleven materials are also summarised in this paper. [ABSTRACT FROM AUTHOR]

The fatigue crack at the rib-to-deck joint that initiated at the weld root and propagated through the deck plate is one of the most common and unfavorable crack types on orthotropic steel deck (OSD). To evaluate the fatigue performance of OSD during its life-cycle in a more accurate way, a numerical simulation method to reproducing the behavior of this type of crack was established based on linear elastic fracture mechanics (LEFM) in this paper. Firstly, the crack growth at the weld root was provided by the fatigue test using the beach marking method. Then, by adopting the proposed crack propagation simulation method, the crack growth in the test was simulated and the fatigue cracks growth life was predicted. Finally, some factors that may have a great influence on crack propagation behaviors were analyzed, including the lack of penetration defects (LOP) at the weld root, the angle between the crack surface and the deck plate, initial crack depth as well as crack aspect ratio. Accordingly, a practical approach was put forward to estimate the fatigue life based on the test, which can be applied to actual structures that are manufactured by the same process of the specimens, and the inspection and maintnenance works can be benefitted. [ABSTRACT FROM AUTHOR]

Exposed to the cyclic action of wind and waves, offshore wind structures are subject to fatigue deterioration processes throughout their operational life, therefore constituting a structural failure risk. In order to control the risk of adverse events, physics-based deterioration models, which often contain significant uncertainties, can be updated with information collected from inspections, thus enabling decision-makers to dictate more optimal and informed maintenance interventions. The identified decision rules are, however, influenced by the deterioration model and failure criterion specified in the formulation of the pre-posterior decision-making problem. In this paper, fatigue failure criteria are integrated with Bayesian networks and Markov decision processes. The proposed methodology is implemented in the numerical experiments, specified with various crack growth models and failure criteria, for the optimal management of an offshore wind structural detail under fatigue deterioration. Within the experiments, the crack propagation, structural reliability estimates, and the optimal policies derived through heuristics and partially observable Markov decision processes (POMDPs) are thoroughly analysed, demonstrating the capability of failure assessment diagram to model the structural redundancy in offshore wind substructures, as well as the adaptability of POMDP policies. [ABSTRACT FROM AUTHOR]

Due to their remarkable advantages, composite adhesively bonded joints are intensively used in many engineering fields. There are many investigations performed by researchers to study the fracture behavior of the adhesively bonded joints. However, there exist discrepancies between the numerical predictions and the experimental results in some cases. This paper reports an investigation on the finite fracture behavior of composite adhesively bonded joints subjected to four-point bending. Experiments are performed for composite adhesively bonded joints with four different configurations. The fracture behavior is observed experimentally by utilizing a high-speed camera. The failure analysis employing the energy-stress coupled criterion is performed. The experimental results are compared with the numerical predictions by using an experimental-based approach where both geometric nonlinearity and interfacial energy are considered. Numerical illustrations are carried out to assess the effect of interface energy, geometric nonlinearity, joint type and dimensions on the fracture behavior of the considered bonded joints. [ABSTRACT FROM AUTHOR]

The current paper provides a procedure for adjusting the failure strain of shell elements based on both mesh size and stress triaxiality. This procedure is a general framework that gives a homogenisation of a neck over the entire length of an element and it uses an arbitrary forming limit diagram (FLD) and stress triaxiality-based failure criterion as input. In the example given in this paper, a Swift FLD is used together with the plane stress version of the modified Mohr–Coulomb failure locus. The results of this study show that simply scaling a failure locus is not correct. The proposed method produces the same mesh size correction for uniaxial tension as prior studies, but it produces different levels for other states of stress. In the limit of very large element sizes, it degenerates to the FLD. [ABSTRACT FROM PUBLISHER]

Curling stresses in rigid pavements are the result of temperature gradient through the thickness of the concrete slab. These stresses have a periodic nature, and the induced cyclic flexural curling stresses lead to the cracking of the concrete slab. In a previous research by the authors, a phase change material (PCM)-rich concrete overlay was proposed as an effective method to control this failure mechanism. A PCM-rich concrete overlay is a concrete surface layer that contains a relatively high percentage of PCM. In the previous study, a phenomenological approach was employed, and it was demonstrated that the incorporation of PCM improves the curling fatigue performance of the concrete slab. Using fracture mechanics, this paper builds upon the findings of the previous study, and it serves as a mechanistic verification of the conclusions of the previous work. A modified Paris' Law was adopted to calculate the cumulative fatigue-fracture damage of the concrete slab due to cyclic thermally-induced curling stresses. The findings of this research demonstrated that the PCM-modified concrete slab undergoes a curling-induced fracture process that is less severe than the slab without the PCM. The impact of this reduction was quantified in terms of an improved fatigue-fracture performance of the pavement. [ABSTRACT FROM AUTHOR]

An introduction is presented in which the editor discusses articles in the issue on topics including asphalt concrete and composite, the mechanism of cracking and the influence of tack coat application.

Glued-in Rods (GiR) are among the high-performance joining technologies used in timber engineering. Engineering design procedures for GiR almost exclusively regulate softwood and softwood engineered wood products (EWP) under quasi-static loads. Since the use of hardwood is expected to significantly increase due to climate change, and potentially establish itself as predominant in Europe's forests, GiR in combination with hardwood and corresponding EWP need to be investigated. Timber constructions subjected to cyclic loads are increasingly being used, as for example in timber bridges, high rise buildings, and wind turbine towers. No normative regulation is yet available for fatigue of GiR, which is for most part due to incomplete or completely missing experimental data. This paper is the first of a two part series; it presents fatigue investigations on GiR in combination with hardwood EWP with different types of rods, wood species and adhesives. Further, the embedment length and stress ratio were varried. In total, more than 70 cyclic tests were performed resulting in a high number of SN-curves showing the fatigue characteristics of GiR. The results show that two different damage mechanisms exist: in low cycle fatigue range (LCF), timber and adhesive fracture become dominant, while rod failure is the limiting factor in high cycle fatigue range (HCF). Based upon the documented experimental findings, existing standards for cyclic load on softwood connection technologies were discussed. The compagnion paper will present a design methodology based on a wood damage accumulation, giving a complete picture combined with existing metal fatigue models. [ABSTRACT FROM AUTHOR]

Glued-in rods (GiR) represent a very successful type of adhesively bonded joints in timber engineering. Despite their apparent geometrical simplicity, their dimensioning still challenges practitioners. A major source of mechanical complexity resides in the orthotropic nature of the wood, or engineered wood products, as laminated veneer lumber (LVL). This paper presents a relatively simple design approach based upon fracture mechanics (FM) and associated double-cantilever beam (DCB) tests that complemented tensile tests for material characterisation. In comparison with the state-of-the-art related to FM in timber engineering, the paper presents a practitioner oriented approach of a yet complex set of GiR geometries involving beech LVL (M16-8.8 threaded rods embedded in cross sections of 120 × 120 mm2 and embedment lengths of 96mm, 128mm and 160mm). The developed numerical model resulted in a good description of the load-displacement of a series of full scale, including very good estimates of their load capacities. Additionally, it allowed for significant insights regarding the complicated relationship between geometry, orthotropy, strength of the component and failure of the GiR, as for examples the complex fracture process, and the importance of transverse tensile stresses, which play a preponderant role, equal in importance to shear stresses. [ABSTRACT FROM AUTHOR]

Since piezoelectric materials are mainly used as sensitive components, various defects such as cracks, cavities, and inclusions have a critical influence on the application of materials. Based on the study of the dynamic anti-plane characteristics for radial crack emanating from a circular cavity in piezoelectric bi-materials, this paper aims to establish the mechanical model of interfacial cracks emanating from an eccentric circular cavity. Green function method, coordinate transformation method, conjunction and crack-deviation techniques are adopted to solve Fredholm's equations, expressing the dynamic stress intensity factor (DSIF) theoretically. As cases, numerical results of DSIFs are plotted and discussed with different geometric and physical parameters by Fortran program. Eccentric defects exist more widely in materials and have higher difficulty in solving, compared with non-eccentric ones. Numerical results show that the dynamic stress intensity factor at the crack tip of the eccentric model is greater than that of the non-eccentric model, which indicates that the eccentricity of the cavity is more likely to cause crack growth and damage to piezoelectric materials. Therefore, it is of great theoretical and engineering significance to study the fracture behavior of materials based on eccentric defects. [ABSTRACT FROM AUTHOR]

This paper studies the parametric design of multilayered piezoelectric/piezomagnetic (PE/PM) ceramic transducer with periodic interfacial electrodes based on fracture mechanics analysis. The analysis of multilayered PE/PM transducer under electrically actuated mode is carried out by means of solving the magneto-electroelastic problem of a PE/PM bi-layer, where the inner interfacial electrode is electrically charged and periodic conditions are used. Due to the singular stress distributed on the inner side of the electrode ends, cracks are prone to nucleate and propagate along the interfaces. The weight function method and linear superposition are used to find the Stress Intensity Factor (SIF) around the crack tip. Parametric discussion was carried out for the dependence of SIF on the layer thickness ratio as well as the position of the interfacial electrode. Analysis reveals that, under the same electric load, a thicker piezoelectric layer will lead to a lower SIF. This suggests that, for the bonded interfaces with certain fracture toughness in the piezoelectric/piezomagnetic transducer, the design with a thicker piezoelectric layer can sustain a higher threshold electric load and the transducer can accommodate more electric charges under the critical condition. However, concerning with the crack extension rate defined as the crack extension induced by per unit electric charge increase, the design with a thinner piezoelectric layer will find a lower and relative small crack extension rate, while for the case of thicker piezoelectric layer, the crack extension rate enhances significantly as crack propagates, which may lead to fatal destruction of the device. [ABSTRACT FROM AUTHOR]

This paper defines in-plane displacement functions of a composite lattice rectangular plate, which is assumed to be a Kirchhoff-Love plate. It presents an approximate method based on the continuous model of conducting a progressive failure analysis for predicting material failure and post-failure behavior of the composite lattice rectangular plate with various boundary and load conditions. To define the approximate method, we use the Ritz method and Hashin's failure criteria. The validity of the present method is verified by comparing the results of the finite element analysis. Finally, we perform parametric and sensitivity analyses to investigate the effects of the design parameters on the failure characteristics of the composite lattice rectangular plates based on the present method. The results allow a database to be obtained on the structural characteristics of composite lattice rectangular plates. Consequently, it is concluded that the present method is well suited to progressive failure analysis of composite lattice rectangular plates due to their relative simplicity and computational efficiency. [ABSTRACT FROM AUTHOR]

This paper derives analytical predictions for notched cross-laminated timber (CLT) plate delamination using fracture mechanics for crack propagation from the notch root. The analysis accounts for both CLT heterogeneity and residual stresses caused by seasonal variations in temperature and humidity. The accuracy of predictions coupled with shear corrections, was confirmed by comparison to finite element analysis. The fracture mechanics approach was validated as appropriate by comparison to recent experiments on notched CLT beams. Residual stress effects are significant and depend strongly on notch depth. Environmental changes that promote swelling, such as increases in temperature or moisture content, are more detrimental to plate integrity than are changes that promote shrinkage. Relatively modest levels of swelling stress can potentially cause spontaneous delamination. A new design guide for notched CLT plates that includes effects of heterogeneity and residual stresses is proposed. [ABSTRACT FROM AUTHOR]

Presents information on research papers presented at the 6th International Conference on the Fundamentals of Fracture held in Cirencester, England from March 26 to 30, 2001. Exploration of basic processes of fracture by researchers; Members of the organizing committee of the conference.

Damage equivalent to that seen over very long times in Grade 91 steel welded components was successfully formed in laboratory, feature sized samples tested under controlled conditions. This paper compares the creep behaviour of welds made using a typical preparation with results for novel step weld geometries. When well-designed the step geometry offsets the heat affected zone (HAZ) in the through thickness of the weld which would be equivalent to the pressure boundary in a pipe. The step in the weld profile thus provides benefit to in-service performance because it prevents the rapid link up of aligned creep cavitation that forms in the HAZ of welds made using typical preparations. The results demonstrate that a well-designed step weld geometry increases the creep rupture life and improves damage tolerance. In turn, the increased duration of stable crack growth promotes the opportunity for detection of creep damage using nondestructive testing methods. [ABSTRACT FROM AUTHOR]

This paper discussed the reasons and the harms of high-speed railway's roadbed settlement in collapsible loess area. On the basis of the experimental simulation and mechanical analysis, the mechanism of fracture grouting is concluded, and a set of upper grouting test equipment is developed as well. Through a set of tests under different grouting pressures, and analyses on the soil's mechanical properties and displacement variations, a quadratic approximation formula is gained. Meanwhile, the mechanism for fracture grouting and the validity of laboratory simulation is tested and verified. In addition, the effect of fracture grouting on high-speed railway's roadbed consolidation in collapsible loess area is also got by fieldqs trial. The results of the current paper provide guide and reference for studying fracture grouting in collapsible loess area. [ABSTRACT FROM AUTHOR]

A dent is one of the main structural damages that may affect ultimate strength. In this paper, the residual ultimate strength of dented metallic pipes subjected to a bending moment is quantitatively investigated. The numerical model is developed accounting for the variation of the dent length (ld), dent depth (dd), dent width (wd), dent rotation angle (θd) and dent location based on ABAQUS Python. The numerical model is validated by test results from a four-point bending test. Subsequently, a parametric investigation is performed on the effects of wave-type initial imperfection, D/t and dent geometrical parameters. It is found that both ld and dd have a significant effect on the residual ultimate strength of dented metallic pipes, while the effect of wd is slight. Finally, an empirical formula with respect to ld and dd has been proposed for the prediction of bending moment, which can be deployed for practical purposes. [ABSTRACT FROM AUTHOR]

In this paper, the cohesive zone modeling (CZM) method has been employed to simulate static and fatigue debonding growth in adhesively bonded composite joints containing bolts as crack stoppers. The cracked-lap shear specimen (CLS) for static and fatigue loads and the wide single-lap shear (WSLS) structural element for static load have been modeled. In both cases, mixed-mode I+ II loading conditions are present in the bondline. Bonded and bonded/bolted configurations of the specimens have been analysed in order to evaluate the efficiency of bolts as crack stoppers. Numerical simulations have been performed using the LS-DYNA FE code. For the static debonding simulation, a standard bilinear traction-separation law has been applied while for the simulation of fatigue debonding growth a modified traction-separation law has been implemented using experimental data derived from fatigue tests. The modification has been realized by means of a user-defined subroutine (UMAT) having the capacity to account for crack divergence by making use of a crack front detection algorithm based on effective element's length. A parametric study on the effect of distance between bolts and crack-tip has been performed. Additionally, the WSLS structural element has been subjected to impact load aiming to create a realistic initial disbond scenario. The residual strength of the element has been predicted by applying a quasi-static load after impact. The numerical results reveal that the presence of bolts under certain circumstances can cause crack growth retardation, under both static and fatigue loading conditions. This study emphasizes on the importance of fatigue crack growth simulation and aims to contribute to the numerical design of crack stopping features as a means of complying towards certification of adhesive bonding in primary composite aircraft structures. [ABSTRACT FROM AUTHOR]

One of the key issues on orthotropic steel deck (OSD) is the reduction of serviceability due to fatigue cracks even though the bridge still keeps a certain level of robustness itself, and accurately simulating crack growth process becomes crucial to evaluate the fatigue performance of OSDs. This paper proposes to measure the fatigue damage based on the two-stage crack growth model derived from experimental tests on the rib-to-deck welded joint of OSD. With the traffic data acquired by the weigh-in-motion system, the consideration of the near-threshold region, i.e., Stage I in the model, turns to be significant as the effect of the vehicle overload is shown more prominently. Thereupon, the way of fatigue damage evaluation is applied to each vehicle to quantify the severity of heavy vehicles with respect to the current status of the crack, and consequently to propose that the permit checking can be implemented in a more direct and dynamic way. The results can be valuable in the fatigue assessment that considers the remedial measures in the life-cycle of OSDs, e.g., the European Convention of Constructional Steelwork (ECCS) procedure, or in developing the guidance for the maintenance of specific bridges with OSDs. [ABSTRACT FROM AUTHOR]

An in-depth understanding of the role of non-metallic inclusions (NMIs) in the hydrogen-induced failure of structural materials is important in the manufacture and application of steels. In this paper we investigated the type, the amount and the distribution of NMIs in pipeline steels and their relation to the susceptibility to hydrogen-induced cracking (HIC). Scanning Electron Microscope (SEM) observation confirmed the interlinking of the microcracks formed at the inclusion-matrix interfaces. By combining with the nondestructive three-dimensional (3D) mapping of crack propagation paths, based on the synchrotron tomography technique, we obtained direct evidence that the cracking initiation at the NMIs and then interlinking on the (nearly) same plane are the main mechanism of HIC failure in X70 steels. We built an elastic-energy-based model, which can be applied to quantitatively predict the HIC-induced dependence of the fracture toughness on NMIs, based on statistical information of the NMIs. The theoretical results show a good agreement with the experimental observation. We proposed a criterion to determine the susceptibility to HIC by the observation of NMIs. We also developed a thermodynamics-based model to analyze the hydrogen trapping at the inclusion-matrix interface and its dependence on the strength of the steel matrix. For the first time, the direct relationship between NMIs and HIC-induced degradation of fracture toughness is obtained. [ABSTRACT FROM AUTHOR]

This paper considers the fast, effective imaging of a perfectly conducting crack(s) in a 2-D homogeneous medium using data measured on its boundary. Based on the structure of singular vectors of the Multi-Static Response (MSR) matrix, whose elements are normalized by a suitable test function at several frequencies, we introduce a weighted subspace migration imaging functional. Based on the relation with the Bessel functions of integer order, it is verified that this is an improved version of traditional subspace migration. Numerical experiments for small and extended cracks from noisy synthetic data support our analysis. [ABSTRACT FROM PUBLISHER]

Experimental creep crack growth data are generally obtained by following standard methods such as ASTM E1457-07 and subsequently characterised using the C* parameter. These data are then used in assessment procedures, such as R5, together with reference stress estimates of C* in the component, to predict creep crack growth behaviour. Some modifications to the ASTM E1457 creep crack growth testing and analysis methods have already been proposed following a previous analysis of data from long term creep crack growth tests on type 316H parent material. This paper reports the results of creep crack growth tests on type 316H heat affected zone material at 550°C using compact tension (CT) specimens manufactured from non-stress relieved thick section butt welds. It is shown that interpretation of the data from these weldment tests is complicated by both the discontinuous nature of the cracking process and the presence of significant residual stresses in the CT specimens. Further modifications to creep crack growth testing and analysis methods are proposed to address difficulties arising from the discontinuous nature of the cracking process, and further work is identified to investigate the influence of the residual stresses present in the specimens on the observed crack growth behaviour. [ABSTRACT FROM AUTHOR]

Degradation branching is a common phenomenon in many real-life applications. The degradation of a location not only increases with time, but also propagates to other locations in the same system. While the degradation of an individual location has been studied extensively, research on degradation branching is sparse. In this paper, we develop a general stochastic degradation branching model that characterizes both the degradation growth and degradation propagation. The probabilistic properties of the general degradation branching processes are analyzed. Reliability metrics such as the mean time to failure, mean residual life, failure probability and others are also investigated. In particular, closed-form expressions for the expectation and variance of the degradation and selected reliability metrics are obtained when the time to branch follows an exponential distribution. The model is validated using actual crack growth data. [ABSTRACT FROM AUTHOR]