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Zero-failure reliability testing aims at demonstrating whether the product has achieved the desired reliability target with zero failure and high confidence level at a given time. Incorporating accelerated degradation testing in zero-failure reliability demonstration test (RDT) facilitates early failure in high reliability items developed within short period of time to be able to survive in fiercely competitive market. The paper aims to discuss these issues.

The triangular cyclic stress uses one test chamber thus saving experimental cost. The parameters in model are estimated using maximum likelihood methods. The optimum plan consists in finding out optimum number of cycles, optimum specimens, optimum stress change point(s) and optimum stress rates.

The optimum plan consists in finding out optimum number of cycles, optimum specimens, optimum stress change point(s) and optimum stress rates by minimizing asymptotic variance of estimate of quantile of the lifetime distribution at use condition subject to the constraint that total testing or experimental cost does not exceed a pre-specified budget. Confidence intervals of the design parameters have been obtained and sensitivity analysis carried out. The results of sensitivity analysis show that the plan is robust to small deviations from the true values of baseline parameters.

For some highly reliable products, even accelerated life testing yields little failure data of units in a feasible amount of time. In such cases accelerated degradation testing is carried out, wherein the failure termed as soft failure is defined in terms of performance characteristic of the product exceeding its critical (threshold) value.

The purpose of this paper is to study the effect of mean stress and stress amplitude on the asymmetric cyclic deformation behavior of SA333 Gr-6 C-Mn steel. Such type of loading may arise during the service period because of the load fluctuations, thermal gradients and sudden loading like seismic events. Tests were also carried out at different temperatures to understand the effect of it on sensitiveness of the materials deformation behavior.

Cylindrical specimen of 8-mm gauge diameter and 15-mm gauge length was fabricated from the pipe section along its axis. Stress controlled ratcheting tests were carried out by using triangular waveform for cyclic loading. The strain accumulations were measured using 12.5-mm gauge length extensometer. Ratcheting tests were carried out at fixed stress amplitude of 400 MPa and mean stress varying from 0 to 75 MPa, whereas at the fixed mean stress of 100 MPa and stress amplitude varies from 300 to 400 MPa at 300°C. To study the effect of temperature on ratcheting behavior, tests were carried out at a load of 100 MPa mean stress and 350 MPa stress amplitude, with a varying temperature between room temperature and 350°C. The stress rate of 115 MPas-1 was kept constant for all the tests.

Increase in mean stress and stress amplitude, ratcheting strain and plastic strain amplitude increases, whereas ratcheting life decreases. With an increase in temperature, ratcheting life increases and strain accumulation decreases up to 300°C, whereas on further increase in temperature, strain accumulation increases with reduction in ratcheting life. Minimum ratcheting rate was observed at 250°C and 300°C. The dynamic strain aging (DSA) phenomena lead to the hardening of the material. The investigated steel shows DSA temperature regime lies between 250°C and 300°C. The failure modes at 250°C and 300°C temperature was transgranular, whereas at 350°C complete ductile.

The stress rate and loading condition may vary to study the ratcheting behavior.

From this study, the critical cyclic load may be determined. The DSA temperature regime of this material is determined at this stress rate. This could help to evaluate the cyclic deformation behavior of the material with temperature changes.

In this investigation, the DSA temperature regime has been determined where maximum ratcheting life, minimum strain accumulation and ratcheting rate were observed. The critical load where the minimum life of the material occurred at elevated temperature is 100 MPa mean stress and 400 MPa stress amplitude.

Gives a bibliographical review of the finite element methods (FEMs) applied for the linear and nonlinear, static and dynamic analyses of basic structural elements from the theoretical as well as practical points of view. The range of applications of FEMs in this area is wide and cannot be presented in a single paper; therefore aims to give the reader an encyclopaedic view on the subject. The bibliography at the end of the paper contains 2,025 references to papers, conference proceedings and theses/dissertations dealing with the analysis of beams, columns, rods, bars, cables, discs, blades, shafts, membranes, plates and shells that were published in 1992‐1995.

The purpose of this paper is to present a new numerical model based on a combined finite-discrete element method, capable of predicting the behaviour of reinforced concrete structures under dynamic load up to failure.

An embedded model of reinforcing bars is implemented in combined finite-discrete element code. Cracking of the structure was enabled by a combined single and smeared crack model. The model for reinforcing bars was based on an approximation of the experimental curves for the bar strain in the crack. The developed numerical model includes interaction effects between reinforcement and concrete and cyclic behaviour of concrete and steel during dynamic loading.

The findings provide a realistic description of cracking in the concrete structure, where all non-linear effects are realized in joint elements of the concrete and reinforcing bars. This leads to a robust and precise model for non-linear analysis of reinforced concrete structures under dynamic load.

This paper presents new robust finite-discrete element numerical model for analysis and prediction of the collapse of reinforced concrete structures. The model is capable of including the effects of dynamic loading on the structures, both in the linear-elastic range, as well as in the non-linear range including crack initiation and propagation, energy dissipation due to non-linear effects, inertial effects due to motion, contact impact, and the state of rest, which is a consequence of energy dissipation in the system.

The purpose of this study is to increasing the gauge factor, reducing the hysteresis error and improving the stability over cyclic deformations of a conductive polylactic acid (CPLA)-based 3D-printed strain sensor by modifying the sensing element geometry.

Five different configurations, namely, linear, serpentine, square, triangular and trapezoidal, of CPLA sensing elements are printed on the thermoplastic polyurethane substrate material individually. The resistance change ratio of the printed sensors, when loaded to a predefined percentage of the maximum strain values over multiple cycles, is recorded. Finally, the thickness of substrate and CPLA and the included angle of the triangular strain sensor are evaluated for their influences on the sensitivity.

The triangular configuration yields the least hysteresis error with high accuracy over repeated loading conditions, because of its uniform stress distribution, whereas the conventional linear configuration produces the maximum sensitivity with low accuracy. The thickness of the substrate and sensing element has more influence over the included angle, in enhancing the sensitivity of the triangular configuration. The sensitivity of the triangular configuration exceeds the linear configuration when printed at ideal sensor dimensional values.

The 3D printing parameters are kept constant for all the configurations; rather it can be varied for improving the performance of the sensor. Furthermore, the influences of stretching rate and nozzle temperature of the sensing material are not considered in this work.

The sensitivity and accuracy of CPLA-based strain sensor are evaluated for modification in its geometry, and the performance metrics are enhanced using the regression modelling.

A method is presented by which elastoplastic constitutive relations for the solid material equivalent to a perforated plate can be obtained, by performing numerical experiments employing the finite element method. The method is applied to a plate of elastic‐perfectly plastic material, perforated in an equilateral triangular penetration pattern of circular holes. The following situations are considered: plane stress, as existing in thin plates under in‐plane loading, generalized plane strain, which approximates the behaviour of thick plates subjected to in‐plane loading and the plate bending condition. First results have been obtained for the plane stress situation. These results show that, for the case of monotonic loading, the elastoplastic behaviour is nearly isotropic in the plane of the plate, whereas under cyclic loading below the limit load, the equivalent solid material exhibits distortional hardening.

Fatigue crack growth models based on elastic‐plastic stress‐strain histories at the crack tip region and strain‐life damage models have been proposed. The UniGrow model fits this particular class of fatigue crack propagation models. The residual stresses developed at the crack tip play a central role in these models, since they are applied to assess the actual crack driving force. This paper aims to assess the performance of the UniGrow model based on available experimental constant amplitude crack propagation data, derived for several metallic materials from representative Portuguese bridges. It also aims to discuss key issues in fatigue crack growth prediction, using the UniGrow model, in particular the residual stress computation and the suitability of fatigue damage rules.

The UniGrow model is assessed using data derived by the authors for materials from Portuguese riveted metallic bridges. Strain‐life data, from fatigue tests on smooth specimens, are used to propose a convenient fatigue damage model. Predicted crack growth rates are compared with experimental crack propagation data obtained by authors using fatigue tests on compact tension specimens. Since the UniGrow model is a residual stress‐based propagation model, elastoplastic finite element analysis is proposed for comparison with the analytical approach implemented in the original UniGrow model.

The use of the Smith‐Watson‐Topper damage parameter overestimates the stress R‐ratio effects on crack propagation rates, mainly if the material shows crack propagation rates with small to moderate sensitivity to stress R‐ratio, which is the case of the materials under investigation in this paper. Alternatively, the application of the Coffin‐Manson damage law leads to consistent fatigue crack growth predictions for the investigated range of positive stress R‐ratios. The stress R‐ratios effects may be solely attributed to the residual stresses. Their estimation, using an analytical approach, may lead to inconsistent results, which is demonstrated by an alternative elastoplastic finite element analysis.

Contributions for more accurate predictions of fatigue crack propagation rates, for several stress ratios, using a strain‐based approach is proposed. This approach is valuable since it may be used to reduce the time consuming and costly fatigue crack propagation tests. Furthermore, the proposed approach shows potential for an unified crack initiation and propagation approach.

The paper aims to verify the influence of mechanical factors (longitudinal elongation at constant stretching velocity, constant elongation strain and cyclic compressive and tensile stresses) on the electrical properties of thin-film and polymer thick-film resistors on flexible substrates.

Kapton foil was used as a substrate for all test samples. Designed resistive structures were made with the aid of two polymer thick-film resistive inks or OhmegaPly Ni-P resistive foil. Two different topologies – the horseshoe and triangular – were used. These topologies should have the opposite stability parameters.

Almost all presented data confirm the influence of the topology of resistors on stability of their electrical properties. The resistive materials applied for test structures also affect the stability under various mechanical exposures.

In general, the largest changes were caused by longitudinal elongation at constant stretching velocity, whereas other tests caused smaller changes of electrical properties. The measurements confirm the influence of topology on stability of electric properties.

Since failure of laminated composites by delaminations is common, the purpose of this paper is to present a numerical procedure to check the stability of delaminations in fiber metal laminate (Glare), with different possible damage configurations, under uni-axial tension. Deformation behavior of the laminate is also examined. Influence of the type and the extent of damage, represented by varying sizes and number of delaminations, on delamination driving force and laminate deformation is found.

Delaminated Glare is modeled by finite element method. Interface cohesive elements are used to model the delaminations. Finite element results provide the deflection/deformation characteristics of the laminate. Driving forces of delaminations are estimated by J integrals that are numerically obtained over cyclic paths near delamination tips. Laminates with different types of delaminations are also fabricated and externally delaminated for measurement of their interlaminar fracture toughness. The delamination is considered to be stable if its driving force is less than corresponding interlaminar fracture toughness of the laminate.

Delaminations are found to be stable in laminates with lower number of delaminations and unstable in laminates with higher number of delaminations. Increase in size of delaminations increases the deformations but reduces the delamination driving force whereas increase in number of delaminations increases both deformations and driving forces. The trends change in case of laminates with symmetrical damage. Shape of delamination is also found to influence the deformations and driving forces. The finite element model is validated.

There is scope for validating the numerical results reported in the paper by theoretical models.

Checking the stability of delaminations and their effect on deformation behavior of the laminate helps is assessment of safety and remaining life of the laminate. If failure is predicted, preemptive action is taken by using repair patch ups at identified critical locations in order to avoid failures in service conditions.

The paper offers the following benefits: use of cohesive zone method that is readily possible in finite element procedures and is relatively simple, fast and reasonably accurate is demonstrated; suitability of using J integrals over paths crossing non-homogeneous and property mismatched material layers is tested; and influence of the type and the extent of damage in the laminate on its deformation behavior and delamination driving forces is found. This type of work has not been reported so far.

Recently, a new class of fatigue crack growth models based on elastoplastic stress‐strain histories at the crack tip region and strain‐life fatigue damage models have been proposed. The fatigue crack propagation is understood as a process of continuous crack initializations, over elementary material blocks, which may be governed by strain‐life data of the plain material. The residual stresses developed at the crack tip play a central role in these models, since they are used to assess the actual crack driving force, taking into account mean stresses and loading sequential effects. The UniGrow model fits this particular class of fatigue crack propagation models. The purpose of this paper is to propose an extension of the UniGrow model to derive probabilistic fatigue crack propagation data, in particular the derivation of the P–da/dN–ΔK–R fields.

An existing deterministic fatigue crack propagation model, based on local strain‐life data is first assessed. In particular, an alternative methodology for residual stress computation is proposed, based on elastoplastic finite element analysis, in order to overcome inconsistencies found in the analytical approximate approaches often used in literature. Then, using probabilistic strain‐life fields, a probabilistic output for the fatigue crack propagation growth rates is generated. A new probabilistic fatigue field is also proposed to take mean stress effects into account, using the Smith‐Watson‐Topper (SWT) damage parameter. The proposed models are assessed using experimental data available for two materials representative from old Portuguese bridges.

A new method to generate probabilistic fatigue crack propagation rates (P–da/dN–ΔK–R fields) is proposed and verified using puddle iron from old Portuguese bridges, usually characterized by significant scatter in fatigue properties. Also, a new probabilistic fatigue field for plain material is proposed to deal with mean stress effects.

A relation between the P–ε–N and the P–da/dN–ΔK–R fields is firstly proposed in this research. Furthermore, a new P–SWT–N field is proposed to deal with mean stress effects.