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This paper outlines progressive damage characteristics of screwed single-lap CFRPI-metal joints subjected to tensile loading at RT (room temperature) and 350°C. Quasi-static tensile tests were performed on screwed single-lap CCF300/AC721-30CrMnSiA joint at RT and 350°C, and the load versus displacement curve, strength and stiffness of joint were gauged and discussed. With due consideration of thermal-mechanical interaction and complex failure mechanism, a modified progressive damage model (PDM) based on the mixed failure criterion was devised to simulate progressive damage characteristics of screwed single-lap CCF300/AC721-30CrMnSiA joint, and simulations correlate well with experiments. By using the PDM, the effects of geometry dimensions on mechanical characteristics of screwed single-lap CCF300/AC721-30CrMnSiA joint were analyzed and discussed.

This paper seeks to deal with progressive damage behaviors of woven composite laminates subjected to low-velocity impact (LVI), tension-after-impact (TAI) and compression-after-impact (CAI). The LVI, TAI and CAI tests were conducted on woven carbon fibre lamina 3238A/CF3052 and woven glass fibre lamina 3238A/EW250F, and the time-dependent LVI contact force and deflection curves, static TAI and CAI load versus displacement curves were determined and discussed. A modified progressive damage model was presented for explicit dynamic LVI and implicit static TAI and CAI analysis by using basic material properties and geometrical dimensions, and progressive damage LVI, TAI and CAI behaviors of woven composite laminates were simulated, demonstrating a good correlation between simulations and experiments.

An engineering approach for fatigue life prediction of fibre‐reinforced polymer composite materials is highly desirable for industries due to the complexity in damage mechanisms and their interactions. This paper presents a fatigue‐driven residual strength model considering the effect of initial delamination size and stress ratio. Static and constant amplitude fatigue tests of woven composite specimens with delamination diameters of 0, 4 and 6 mm were carried out to determine the model parameters. Good agreement with experimental results has been achieved when the modified residual strength model has been applied for fatigue life prediction of the woven composite laminate with an initial delamination diameter of 8 mm under constant amplitude load and block fatigue load. It has been demonstrated that the residual strength degradation‐based model can effectively reflect the load sequence effect on fatigue damage and hence provide more accurate fatigue life prediction than the traditional linear damage accumulation models.

This paper presents an experimental and numerical study of the notch effect on strength and fatigue life of double edge notched (DEN) composite laminates made of woven glass fibre lamina 3238A/EW250F and woven carbon fibre lamina 3238A/CF3052. Experimental results show that the notch effect is dependent on fibre type, notch depth, load type and load sequence. As-n-R-d-r" role="presentation"> s - n - R -d-r residual strength model was proposed to account for the effects of the notch and the stress ratio, and a progressive damage algorithm was developed to predict damage propagation and residual life of composites under spectrum fatigue load. Good agreement between the experimental results and the numerical predictions has been achieved.

This paper attempts to investigate the effects of stress ratio and high temperature on the HCF (high-cycle-fatigue) and VHCF (very-high-cycle-fatigue) behaviors of nickel-based wrought superalloy GH3617M. Fatigue tests over the full HCF and VHCF regimes were conducted on superalloy GH3617M subjected to constant-amplitude loading at five stress ratios of −1, −0.5, 0, 0.4, and 0.8 in environments of 20 °C and 700 °C temperatures. From experimental observation and fractographic analysis, fatigue mechanisms were deduced to reveal the synergistic interaction between high temperature and stress ratio on the HCF and VHCF behaviors of superalloy GH3617M. A phenomenological model was crafted from available fatigue design knowledge to evaluate the synergistic interaction, and a good correlation between predictions and experiments has been achieved. Keywords: High cycle fatigue, High-temperature, Nickel-based superalloy, Stress ratio, Very high cycle fatigue

This paper seeks to present a semi-analytical model for predicting the nonlinear tensile properties of corrugated flexible composite skin (FCS) within large deformation range based on iterative integration procedure. The FCS is constructed with two thin-walled curved fibre-reinforced-plastics (FRP) composite shells with a biaxially symmetrical lenticular cross-section, which can be stretched largely along the corrugated direction through pure elastic deformation. Analytical formulations for tensile stiffness of the FCS are derived based on the unit virtual load method, and geometrical equations are established to describe tensile deformation of the FCS. By means of linear elastic and strain energy theory, new geometry and tensile force increment of extended FCS are calculated at a given small increment of tensile displacement. In order to obtain the tensile behaviour of the FCS within large deformation range, semi-analytical model is presented by using the iterative calculation, and then is verified from experiments. Finally, the effect of the geometry on tensile behaviour of the FCS is analyzed numerically.

Triaxial weave fabrics are increasingly used in ultralight structures, such as the wings of unmanned aerial vehicles (UAVs) and deployable antenna on spacecraft. The tensile strength to stiffness ratio for these applications is important, requiring an optimal weave pattern; in this paper Genetic Algorithms are used to improve these designs. The mechanical response is obtained using the minimum total complementary potential energy principle where the yarns are approximated as curved beams in a micromechanical unit cell. Leading Genetic Algorithms are benchmarked to determine which perform best. The results form a disconnected Pareto front where the left hand part can be used for flexible structures but is difficult to find. An overall improvement in strength to stiffness ratio of 1191% is made with 643 designs found better than a current example. The selection of the Genetic Algorithm is shown to be crucial with only MLSGA-NSGAII regularly finding the entire Pareto front.

This paper developed a fatigue crack growth model considering the effects of load interaction and low-velocity impact (LVI) damage. Fatigue crack growth (FCG) accumulative method was established to assess crack growth life of aluminium-alloy thin-sheets with LVI damage under spectrum loading. To validate the proposed model, LVI tests of 7075-T62 aluminium-alloy thin-sheets were conducted, followed by post-impact constant amplitude tension–tension and block spectrum loading FCG tests. Experimental results indicate that there are two competing mechanisms for the effect of LVI damage on the subsequent FCG behaviour of aluminium-alloy thin-sheets. One is the retardation effect on the crack growth rate from the dented plastic zone caused by LVI, and the other is the acceleration effect from the stress concentration due to impact-induced geometric changes. The new FCG model achieves a good agreement with FCG results of post-impact aluminium-alloy thin-sheets and can capture the LVI damage effect, opening an avenue to predict FCG life of aluminium-alloy thin-sheets with LVI damage.

This paper seeks to evaluate crack propagation properties and residual lives of metallic alloys subjected to fatigue loading at room and high temperatures. Fatigue crack growth tests were performed on Ti-6Al-4V/ELI and 7050-T7452 subjected to constant-amplitude and actual random-spectra loading at room temperature of about 25 °C and at high temperatures of 250 °C and 150 °C to determine their crack growth properties and residual lives. The damage mode and mechanisms at high temperature were compared with those at room temperature on the basis of the results of fractographic analysis. Temperature-dependent residual lives under actual random-spectra load history were evaluated based on a modified accumulation damage rule accounting for the load interaction. Good correlation was achieved between the predictions and actual experiments, demonstrating the practical and effective use of the proposed method. Keywords: Crack growth, Fatigue, High temperature, Metallic alloy, Residual life

This paper developed a fatigue-driven residual strength model considering the effects of low-velocity impact (LVI) damage and stress ratio. New fatigue failure criteria based on fatigue-driven residual strength concept and fatigue progressive damage model were developed to simulate fatigue damage growth and predict fatigue life for plain-weave composite laminates with LVI damage. To validate the proposed model, LVI tests of plain-weave glass fibre reinforced polymer 3238A/EW250F laminates were conducted, followed by post-impact constant amplitude tension–tension, compression-compression fatigue tests and multi-step fatigue tests. Experimental results indicate that the LVI damage degrades fatigue strength of plain-weave glass fibre composite laminate drastically. The load history also plays an important role on the fatigue accumulation damage of post-impact laminates. The new fatigue progressive damage model achieves a good agreement with fatigue life of post-impact laminates and is able to capture the load sequence effect , opening a new avenue to predict fatigue failure of composite laminates.

This paper deals with a novel corrugated flexible composite skin (FCS) for morphing application. The FCS is constructed with two thin-walled curved fibre-reinforced-plastics (FRP) composite shells which can be extended through pure elastic deformation during a large deformation process. Thus, the area of the FCS can be changed significantly. Geometrical equations are established for describing the extensional deformation of the FCS. Based on equilibrium equations and laminate theory, analytical solutions are derived for calculating the mechanical properties of the FCS in an extensional deformation process. In order to validate the FCS design and the analytical model, FCS specimens made from T300/5228 prepreg were fabricated using vacuum bag and co-bonding methods. Tensile tests on the FCS specimens were successfully carried out. Load versus displacement curves, tensile stiffness versus tensile load curves and relative deformation versus tensile load curves were measured. Comparisons between the theoretical predictions and the experiments were conducted. It is shown that the predictions using the new model correlates well with the experiments. The theoretical analysis and experimental validation thus show that the new FCS design was effective and feasible.

This paper attempts to assess fatigue lifetime of full-scale composite cabin by using experimental and numerical methods. With due consideration of multiaxial stress state and stress ratio effect, the governing equation for multiaxial fatigue-induced residual strength at an arbitrary stress ratio was derived. Based on multiaxial fatigue-induced residual strength concept, new fatigue-driven failure criterion was devised for progressive damage modelling and fatigue life prediction of composite structures. Quasi-static and step constant-amplitude cyclic loading tests were respectively performed to measure the load versus strain curves and to determine fatigue life and failure mode of full-scale composite cabins. It is shown from experimental observations that fatigue damage first appeared at upper left fillet of cutout, and then propagated from upper left fillet to the nearby countersunk hole, which was followed by the propagation along the circumference direction of cylinder until final failure. A progressive damage model based on fatigue-driven failure criterion was generated for damage mechanism modelling and fatigue life prediction of composite cabin, and the numerical results correlate well with the experimental findings, demonstrating the practical and effective use of proposed failure criterion.

This paper proposes a new analytical model to predict plastic deformation and strain distributions in aluminium-alloy plates under low velocity impact loading. The low velocity impact load on the fully clamped circular plate was idealized as a quasi-static normal point force acting at the centre of plate. Based on apt geometrical approximation and assumptions, governing equations were established to predict the out-of-plane deflection and the radial tensile, radial and circumferential flexure strains in fully clamped conditions. From the deformation theory of plasticity, a new formula was derived to estimate the impact load by incorporating strain-energy approach, bilinear strain-hardening constitutive model and the one-dimensional Tresca yield criterion. Low velocity impact tests were performed to confirm the proposed model and good correlation was achieved between the predictions and actual experiments, demonstrating the practical and effective use of the proposed model.

This paper deals with new analytical solutions to predict tensile and in-plane shear strengths of triaxial weave fabric (TWF) composites accounting for the interaction between angularly interlacing yarns. The triaxial yarns in three directions of 0° and ±60° in micromechanical unit cell (UC) are idealized as the curved beams with a path depicted by using sinusoidal shape functions. The tensile and in-plane shear strengths of TWF composites are derived by means of the minimum total complementary potential energy principle founded on micromechanics. In order to validate the new model, the predictions are compared with experimental data in prior literatures. It is shown that the predictions from the new model agree well with experimental results.

This article presents a new micromechanical model to predict biaxial tensile moduli of plain weave fabric composites by considering the interaction between the orthogonal interlacing strands. The two orthogonal yarns in micromechanical unit cell were idealized as curved beams with a path depicted using sinusoidal shape functions. The biaxial tensile moduli of plain weave fabric composites were derived by means of the minimum total complementary potential energy principle founded on micromechanics. Biaxial tensile tests were conducted on the resin transfer molding–made EW220/5284 plain weave fabric composites at five biaxial loading ratios of 0, 1, 2, 3 and ∞ to validate the new model. Predictions from the new model were compared with experimental data. Good correlation was achieved between the predictions and actual experiments, demonstrating the practical and effective use of the proposed model. Using the new model, the biaxial tensile moduli of plain weave fabric composites can be predicted based only on the properties of basic woven fabric.

This paper addresses the effects of stress ratio on the temperature-dependent high-cycle fatigue (HCF) properties of alloy steels 2CrMo and 9CrCo, which suffer from substantial vibrational loading at small stress amplitude, high stress ratio, and high frequency in the high-temperature environments in which they function as blade and rotor spindle materials in advanced gas or steam turbine engines. Fatigue tests were performed on alloy steels 2CrMo and 9CrCo subjected to constant-amplitude loading at four stress ratios and at four and three temperatures, respectively, to determine their temperature-dependent HCF properties. The interaction mechanisms between high temperature and stress ratio were deduced and compared with each other on the basis of the results of fractographic analysis. A phenomenological model was developed to evaluate the effects of stress ratio on the temperature-dependent HCF properties of alloy steels 2CrMo and 9CrCo. Good correlation was achieved between the predictions and actual experiments, demonstrating the practical and effective use of the proposed method.

A new S - N - R surface model accounting for the stress ratio effect is proposed to depict fatigue behavior, and a modified damage accumulative rule considering the load interaction is presented to assess fatigue lifetimes under random spectra loading. Fatigue tests were performed on notched aluminum-alloys 2524-T3 and 7050-T7451 subjected to constant amplitude and random spectra loading at 25 °C room and −70 °C cryogenic temperatures, and the load-environment interaction and load interaction mechanisms were deduced from fractographic analysis. The new model shows good correlation with experimental results.

New [Formula: see text] surface model is proposed for depicting corrosion fatigue behaviour and novel formulae are derived to estimate the parameters of proposed model by best fitting from a minimal experimental dataset of corrosion fatigue tests. From the Palmgren–Miner rule, a cumulative damage model for the alternation between corrosion and fatigue is developed to evaluate calendar life of metallic structural component. Corrosion tests are conducted on unnotched and notched specimens from LD10CS aluminium alloy and 15CrMnMoVA alloy steel in artificial corrosion environments. Fatigue tests are also performed on corroded specimens subjected to constant amplitude loading and the interaction mechanisms between corrosion and fatigue are deduced from fractographic studies. The applicability of the new models has been shown for experimental datasets for depicting corrosion fatigue behaviour and for evaluating calendar life of motor brace rod in helicopter.

A modified model is developed to characterize and evaluate high-cycle fatigue behavior of Co-based superalloy 9CrCo at elevated temperatures by considering the stress ratio effect. The model is informed by the relationship surface between maximum nominal stress, stress ratio and fatigue life. New formulae are derived to deal with the test data for estimating the parameters of the proposed model. Fatigue tests are performed on Co-based superalloy 9CrCo subjected to constant amplitude loading at four stress ratios of −1, −0.3, 0.5 and 0.9 in three environments of room temperature (i.e., about 25 °C) and elevated temperatures of 530 °C and 620 °C, and the interaction mechanisms between the elevated temperature and stress ratio are deduced and compared with each other from fractographic studies. Finally, the model is applied to experimental data, demonstrating the practical and effective use of the proposed model. It is shown that new model has good correlation with experimental results.

A modified Trantina–Johnson model was developed to characterize corrosion fatigue crack growth behavior. Crack growth accumulative methodology based on the Willenborg–Chang rule was used to evaluate the residual lifetimes of corrosion fatigue crack growth. Fatigue crack growth tests were performed on 2524-T3 and 7050-T7451 aluminum alloys subjected to constant amplitude and random spectra loading under the environments of dry air and 3.5% NaCl sodium chloride solution, and the load–environment interaction and load interaction mechanisms were deduced from fractographic analysis. The developed models showed good correlation with experimental results.

New formulae are derived to predict the normal bypass, transfer and nominal stresses around the fastener holes on multi-fastener mechanical joints under plane stress conditions. A modified method based on the nominal stress concept is developed to evaluate fatigue lives of complex multi-fastener joints. The method is informed by fatigue characteristics of joints with similar structural details. Fatigue tests on two-rivet, four-rivet and eight-rivet joints were performed and damage mechanisms are deduced from fractographs. Good correlation is achieved between the predictions and actual experiments, demonstrating the practical and effective use of the proposed method.

This paper seeks to mark the fruitful collaborative research between scholars in the University of Southampton and Beihang University for last 25 years on structural integrity. Their efforts addressed some important issues in structural integrity such as fatigue and fracture behavior, fatigue load spectra, fatigue and fracture lifetimes, reliability-based service period, adhesively bonded composite patch repairs, Plain Woven Fabric (PWF) composites and composite artefacts. New advances in engineering approaches, experimental methods, numerical algorithms and understanding of failure mechanisms relating to structural integrity are highlighted. Probable limits (or drawbacks) are also discussed. This review provides an insight into the general aspects on structural integrity and constitutes a basis for pointers to the further works on structural integrity. Keywords: Composites, Fatigue, Fracture, Reliability, Repair, Structural integrity

This paper deals with three-point flexure tests on hybrid I- and Π-beams, made out of multi-layer carbon fiber/epoxy resin (including twill woven fabric CF3031/5284 and unidirectional cord fabric U3160/5284) reinforced composites, processed using the RTM (resin transfer molding) technique. Static bending properties were determined and failure initiation mechanism was deduced from experimental observations. Failure mode of the tested hybrid RTM-made I-beams can be reckoned to be characteristic of the delamination from the cutout edge within the web and the debonding propagation along the interface between the inverted triangular resin-rich zone and the adjacent curved web until local buckling within the curved webs around the conjunction fillet region. In contrast, as distinct from hybrid RTM I-beams subjected to three-point bending loading, hybrid RTM-made Π-beams in three-point flexure tests experienced the resin debonding in the inverted triangular resin-rich zones and the debonding propagation along the interface between the inverted triangular resin-rich zone and the adjacent curved web until complete separation of the curved web from the flange. Progressive damage models (PDMs) were presented to predict failure loads and process of hybrid RTM-made I- and Π-beams under three-point flexure. Good correlation was achieved between experimental and numerical results.

This paper deals with mode II interlaminar delamination properties and failure mechanisms of composite laminates in three-point end-notched flexure (3-ENF) tests under fixed cyclic loading. The results for fracture toughness, fatigue driving force and delamination propagation behaviours of three different types of carbon and E-glass fibre/epoxy resin-reinforced composite laminates are evaluated and compared with each other for providing an insight into fatigue damage development in composites and for constituting a fundamental basis for the development of a characterization model. A new characterization formulation is presented for mode II interlaminar delamination propagation based on controlling fatigue stress. Finally, the model is applied to experimental data, demonstrating the practical and effective use of the proposed model. It is shown that fatigue-driven strength for mode II interlaminar delamination propagation can be obtained realistically from experimental data using the new formulae.

This paper seeks to investigate thermal behaviour of a thin-walled deployable composite boom (DCB) in a space environment using ground thermal-vacuum test and FEA methods. Thermal tests simulating a space environment include three key conditions, namely ultra-high level of vacuum (lower than 10 −5 Pa), heat sink (−180 °C) that is realized using black panels with the liquid-nitrogen cooling system and thermal loading that is achieved through infrared lamps. The thermal tests of the DCB under seven typical heat fluxes were conducted to characterize heat transfer mechanisms and to obtain temperature fields. The basic heat transfer methods for the DCB in a space environment were surface radiation, cavity radiation and heat conduction. These led to significant temperature difference and gradient occurring on the irradiated and shadowed parts of the DCB at nighttime and daytime. FE models were established to predict temperature fields and thermally induced deformation. Good correlation was achieved between experimental and numerical results.

This paper outlines an analytical model to predict the temperature of fully-inflated balloon on float at high altitude in stratosphere. Simplified radiative and convective heat transfer models are developed to estimate absorption and emission heat of balloon film and lifting gas within balloon. Thermal equilibrium equations for the balloon system in the day time and night time are derived by incorporating radiative and convective heat transfer models. The new model is applied to calculate the day and night temperatures of the balloon system on float at a high-altitude in stratosphere and reasonable correlation is achieved between the predictions obtained from new models and from prior flight testing data, demonstrating the effective use of the proposed models.

The paper deals with the analytical solutions on geometrical and mechanical properties of ultra-thin-walled lenticular collapsible composite tube (LCCT) in fold deformation for understanding the phenomenon of actual fold deformation and for improving the structural behaviours in engineering application. The LCCT in fold deformation was idealized as the curved thin-walled beam with a biaxisymmetrical lenticular cross-section described by concave and convex tangential circular arcs and with a longitudinal path depicted by using multinomial shape function. New geometrical equations were established for predicting the in-plane strain of the LCCT in fold deformation (consisting of flattening and curling deformation modes) based on apt geometrical approximations and deformation assumptions, and analytical solution was derived for calculating the interlaminar shear stress on the bonding interface of the LCCT by means of equilibrium equation and linear-elastic constitutive equation founded on micromechanics. In order to validate the model, experiments were performed to determine respectively the load–displacement and in-plane strains of the ultra-thin-walled LCCT in the flattening and curling deformation modes and the comparison between the theoretical predictions and the experiments was conducted. It is shown that the predictions from the new models correlate well with the experiments within small deflection range. These efforts are argued to be successful in predicting the fold deformation of ultra-thin-walled LCCT, but limited to small deflection range only.

This paper deals with static pull and push bending tests on two-dimensional (2D) orthogonal EW220/5284 twill weave fabric (TWF) composite tee-joints processed with the resin transfer moulding (RTM) technique. Static pull and push bending properties are determined and failure initiation mechanism is deduced from experimental observations. The experiments show that the failure initiation load, on average, is greater for push bending than for pull bending, whereas the scatter is smaller for push bending than for pull bending. The failure mode of RTM-made tee-joints in pull bending tests can be reckoned to be characteristic of debonding of resin matrix at the interface between the triangular resin-rich zone and the curved web of tee-joint until complete separation of the curved web from the bottom plate. In contrast, as distinct from the products subject to pull bending loading, the RTM tee-joints in push bending tests experience matrix cracking and fibre fracture from outer layers to inner layers of the bottom plate until catastrophic collapse resulting from the bending. Three-dimensional finite element (FE) models are presented to simulate the load transfer path and failure initiation mechanism of RTM-made TWF composite tee-joint based on the maximum stress criterion. Good correlation between experimental and numerical results is achieved.

This paper proposes a new analytical solution to predict the elastic modulus of a 2D plain weave fabric (PWF) composite accounting for the interaction of orthogonal interlacing strands. The two orthogonal yarns in a micromechanical unit cell are idealized as curved beams with a path depicted by using sinusoidal shape functions. The modulus is derived by means of a strain energy approach founded on micromechanics. Four sets of experimental data pertinent to four kinds of 2D orthogonal PWF composites have been implemented to validate the new model. The calculations from the new model are also compared with those by using four models in the earlier literature. It is shown that the experimental results correlate well with predictions from the new model.

Tension and shear tests are carried out on composite cross-joints, produced by resin transfer moulding (RTM), stitch-RTM and cobonding techniques separately, to investigate the influences of different production methods on their mechanical properties and their failure mechanism. It is concluded from test results that, in terms of mechanical properties, the RTM-made cross-joint holds superiority over other two, and both stitch-RTM and cobonding methods have significant adverse effects on mechanical properties. Experimental observation and finite element (FE) numerical simulation show that the delamination first takes place at the upper triangle-like resin-rich zone of joints, then propagates along the interface between the zone and the curved webs/flanges to the bottom plate, and grows along the horizontal bottom plate till failure of the joint accurs at last. Results demonstrate that there is a good agreement between the FE model and the tests.

This paper seeks to address a novel model for predicting the compression modulus of a 2D plain weave fabric (PWF) composite accounting for the interaction of orthogonal interlacing strands. The two orthogonal yarns in a micromechanical unit cell are idealized as curved beams with a path depicted by using sinusoidal shape functions. The modulus is derived by means of a strain energy approach founded on micromechanics. In order to validate the model, experiments have been performed to investigate the mechanical properties of two-dimensional (2D) orthogonal EW220/5284 PWF composites fabricated by resin transfer moulding (RTM). In-plane tensile, compressive and shear moduli have been measured. It is shown that the experimental results correlate well with predictions from the new model.

This paper addresses the static, compressive after impact (CAI) and fatigue properties and the failure mechanisms of T300/QY8911 carbon fibre reinforced composite laminates with different lay-ups to optimize the stacking sequence. Ten different lay-ups have been studied and the results for static strength, CAI and fatigue residual strength under different fatigue stress amplitudes are evaluated and compared with each other. The results of this study provide an insight into fatigue damage development in composites and constitute a fundamental basis for the development of a strain-based residual strength model. A new formulation is presented for a fatigue-driven residual strength surface based on controlling fatigue strain. The parameter determination formulae of the residual strength surface are established to deal with the test data effectively and easily. Finally, the model is applied to experimental data, demonstrating the practical and effective use of the proposed model. It is shown that fatigue-driven residual strength can be obtained realistically from experimental data using the new formulae.

Two new phenomenological expressions for generalized constant-life curves are developed on the basis of a traditional fatigue constant-life curve. Parameter estimation formulae of the generalized constant-life curve are obtained from the standard procedure for regression analysis. From the generalized constant-life curves proposed, two-dimensional joint probability distributions of generalized strength are derived. Finally, the methods developed are used to analyse three sets of experimental data pertaining to the two-dimensional up-and-down tests for LY11 aluminium alloy and fracture threshold tests for aluminium alloy and alloyed steel in order to verify the practicability and validity of the new approaches. These matters have an important role in fatigue and fracture reliability analysis in ultra-long-life regions and need to be resolved.

This paper seeks to establish an integrated and practical data treatment system for actual load history reliability analysis. A convergence–divergence counting procedure is presented to extract all load cycles from a load history of divergence–convergence waves. The lowest number of load history sampling is established on the basis of the damage-based prediction criterion. A parameter estimation formula is proposed for hypothesis testing of the load distribution. The examples of its application for the data treatment of actual load history are given. The proposed data treatment system has been shown to have valid and practical characteristics in analysing reliability results.

This paper outlines two new practical models to evaluate fatigue residual strength and the overall range of life for reliability-based design. A new fatigue-driven residual strength surface model with four parameters is derived based on an expression form of power function product to estimate the parameters more easily and expediently, and logically characterize the physical characteristics and the phenomenological quantitative laws. A more appropriate S-N curve formulation with four parameters is presented to cover overall life range. By means of the likelihood principle and the linear regression, the parameter determination formulae of these two models are respectively established to deal with the test data effectively and easily. The probability distributions for these two models are also given. Finally, the models are applied to two sets of experimental data, demonstrating the practical and effective use of the proposed models. It is shown from these examples that fatigue-driven residual strength and the overall range of life can be obtained realistically according to the small sample test data using the new formulae.

The randomization of deterministic fatigue damage equation leads to the stochastic differential equation and the Fokker-Planck equation affected by random fluctuation. By means of the solution of equation, the probability distribution of fatigue damage with the change of time is obtained. Then the statistical moment of fatigue life in consideration of the stationary random fluctuation is derived. Finally, the damage probability distributions during the fatigue crack initiation and fatigue crack growth are given.

This paper seeks to outline the temperature effect on the buckling properties of ultra-thin-walled lenticular collapsible composite tube (LCCT) subjected to axial compression. The buckling tests of the LCCT specimens subjected to axial compression were carried out on INSTRON-500N servo-hydraulic machine in dry state and at the temperatures of 25 °C, 100 °C and −80 °C. The load–displacement curves and buckling initiation loads were measured and the buckling initiation mechanism was discussed from experimental observations. Experiments show that the buckling initiation load, on average, is only about 2.2% greater at the low temperature of −80 °C than at the room temperature of 25 °C due to the material hardening, demonstrating an insignificant increase in the buckling initiation load, whereas it is about 19.5% lower at the high temperature of 100 °C than at the room temperature owing to the material softening, implying a significant decrease in the buckling initiation load. The failure mode of the LCCT in axial compression tests at three different temperatures can be reckoned to be characteristic of the buckling initiation and propagation around the central region until rupture. The finite element (FE) model is presented to simulate the buckling initiation mechanism based on the eigenvalue-based methodology. Good correlation between experimental and numerical results is achieved.

This work seeks to investigate the notch sensitivity and fracture behaviour of orthogonal Kevlar-plain woven fabric (PWF)- reinforced thermoplastic polyurethanes (TPU) film applied to high altitude balloon. Four types of specimens are implemented to measure notched strength and fracture toughness by conducting static tension and tear tests on an MTS system respectively. The damage and failure mechanisms are discussed and the results for notched strength and tear resistance are evaluated and compared with each other. From the experiments, it is found that the notch sensitivity of the film increases with the increase in the size of the hole, but the notch sensitivity and the stress concentration of the notch are insignificant and there is a decrease of only about 4%-10% in tensile strength for the notched specimens with different hole sizes in diameter compared with the unnotched specimen. In contrast, the tear resistance containing a central slit with only 1 mm length is about half of tensile strength of the unnotched film, which implies that the tear resistance exists an significant notch sensitivity. The results of this study provide an insight into notch sensitivity and fracture behaviour of the Kevlar-PWF-reinforced TPU film and constitute a fundamental basis for the design of high altitude balloon.

This paper proposes a new analytical solution to predict the shear modulus of a two-dimensional (2D) plain weave fabric (PWF) composite accounting for the interaction of orthogonal interlacing strands with coupled shear deformation modes including not only relative bending but also torsion, etc. The two orthogonal yarns in a micromechanical unit cell are idealized as curved beams with a path depicted by using sinusoidal shape functions. The internal forces and macroscopic deformations carried by the yarn families, together with macroscopic shear modulus of PWFs are derived by means of a strain energy approach founded on micromechanics. Three sets of experimental data pertinent to three kinds of 2D orthogonal PWF composites have been implemented to validate the new model. The calculations from the new model are also compared with those by using two models in the earlier literature. It is shown that the experimental results correlate well with predictions from the new model.

This paper seeks to outline a novel three-layer model and a new birth–death element solution technique to evaluate static strength of notched metallic panel repaired with bonded composite patch and to optimize material parameters. The higher order 3D, 8-node isotropic solid element and 8-node anisotropic layered solid element with three degrees of freedom per node are respectively implemented to model substrate panel, adhesive layer and composite patch to establish three-layer model of repaired panel. The new solving technique based on birth–death element is developed to allow solution of the stress pattern of repaired panel for identifying failure mode. The new model and its solution are used to model failure mode and residual strength of repaired panel, and the obtained results have a good agreement with the experimental findings. Finally, the influences of material parameter of adhesive layer and composite patch on the residual strength of repaired panel are investigated for optimizing material properties to meet operational and environmental constraints.