This paper illustrates various dynamic characteristics of open cell compliant polyurethane foam with auxetic (negative Poisson’s ratio) behaviour. The foam is obtained from off-the-shelf open cell polyurethane grey foam with a manufacturing process based on mechanical deformation on a mould in a temperature-controlled oven. The Poisson’s ratio is measured with an image processing technique based on edge detection with wavelet methods. Foam samples have been tested in a viscoelastic analyser tensile test machine to determine the Young’s modulus and loss factor for small dynamic strains. The same samples have also been tested in an acoustic impedance tube to measure acoustic absorption and specific acoustic resistance and reactance with a transmissibility technique. Another set of tests has been set up on a cam plastometer machine for constant strain rate dynamic crushing analysis. All the tests have been carried out on auxetic and normal foam samples to provide a comparison between the two types of cellular solids. The results from the experimental tests are discussed and interpreted using microstructure models for cellular materials existing in the literature. The negative Poisson’s ratio foam presented in this paper shows an overall superiority regarding damping and acoustic properties compared to the original conventional foam. Its dynamic crushing performance is also significantly superior to the normal foam, suggesting a possible use in structural integrity compliant elements.

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A B S T R A C T The paper deals with the multi-axial fatigue strength of notched specimens made of 39NiCrMo3 hardened and tempered steel. Circumferentially V-notched specimens were subjected to combined tension and torsion loading, both in-phase and out-of-phase, under two nominal load ratios, R = −1 and R = 0, also taking into account the influence of the biaxiality ratio, λ = τ a /σ a . The notch geometry of all axi-symmetric specimens was a notch tip radius of 0.1 mm, a notch depth of 4 mm, an included V-notch angle of 90 • and a net section diameter of 12 mm. The results from multi-axial tests are discussed together with those obtained under pure tension and pure torsion loading on plain and notched specimens. Furthermore the fracture surfaces are examined and the size of nonpropagating cracks measured from some run-out specimens at 5 million cycles. Finally, all results are presented in terms of the local strain energy density averaged in a given control volume close to the V-notch tip. The control volume is found to be dependent on the loading mode.Keywords multiaxial fatigue; notch stress intensity factor (NSIF); strain energy density (SED); torsion loading; V-notched. N O M E N C L A T U R E2α = V-notch included angle = Phase angle λ = Biaxiality ratio, τ a /σ a λ 1 = Eigenvalue of the mode I stress distribution, according to Williams's solution λ 3 = Eigenvalue of the mode III stress distribution ρ = Notch root radius σ a = Nominal stress amplitude referred to the net area of the specimens τ a = Nominal stress amplitude due to torsion loading (on the net area) σ A, τ A = Fatigue strength (in terms of stress amplitudes on the net area) at N A cycles to failure σ y = Yield stress σ y = Cyclic yield stress c np = Non-propagating crack length according to Yu, Tanaka and Akiniwa's model e 1 , e 3 = Parameters used for the energy density evaluation k = Inverse slope of the fatigue curves K 1 , K 3 = Mode I and mode III notch stress intensity factors (NSIFs) K th = Threshold value of the stress intensity factor K IIIsh th = Shielding stress intensity factor under mode III loading according to Yu et al. k 1 , k 3 = Non-dimensional factors used in the NSIF expressions Correspondence: P. Lazzarin.

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Crack paths under both fatigue and fracture conditions are governed by the crack tip displacement field and the material deformation characteristics, including those influenced by metallurgical anisotropy. Experimental techniques such as thermoelasticity and photoelasticity have been successfully used to characterise the elastic stress fields around cracks but they do not take into account either plasticity or anisotropy. Considerable work has been carried out to characterise crack tip stress fields from displacement measurements. The current method of choice for obtaining displacement field data is digital image correlation (DIC) which has undergone significant advances in the recent years. The ease of use and capabilities of the technique for full field displacements has led to improved methods for characterising crack tip displacement fields based on data obtained from DIC. This paper gives an overview of some of the applications of DIC for crack tip characterisation such as K, T-stress and crack tip opening angle (CTOA) measurements as well as data obtained from 3D measurements of a propagating crack.

A high strain rate compression test with a constant speed of 1.5 m/s has been performed on samples of negative Poisson's ratio and normal open-cell polyurethane foam. The tests show that the transformation of the normal foam into the auxetic phase greatly increases the crashworthiness qualities of the open-cell foam.

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A B S T R A C T Thermoelastic stress analysis has been developed in recent years as a direct method of investigating the crack tip stresses in a structure under cyclic loading. This is a consequence of the fact that stress intensity factors obtained from thermoelastic experiments are determined from the cyclic stress field ahead of a fatigue crack, rather than inferred from measurement of the crack length and load range. In the present paper the results of fatigue crack growth tests performed on welded ferritic steel plates are reported. From the results it can be observed that the technique is sensitive to the effects of crack closure and the presence of tensile and compressive residual stresses due to welding.Keywords DeltaTherm; differential thermography; fatigue cracks; stress intensity factor (SIF); thermoelastic stress analysis (TSA). N O M E N C L A T U R Ea = crack length A = thermoelastic constant C p = specific heat at constants pressure E = elastic modulus K max = stress intensity factor at maximum load K min = stress intensity factor at minimum load K open = stress intensity factor at the opening load K res = stress intensity factor due to residual stresses m(x, a) = weight function m 1 , m 2 = weight function coefficients R = ratio of the minimum to the maximum load applied S = magnitude of the thermoelastic signal S 0 = residual stress distribution along the crack line T = absolute temperature of the specimen W = specimen width r, θ = notation for polar coordinates x = distance along the crack line y = vertical distance from the crack line α = coefficient of thermal expansion K = stress intensity factor range K eff = effective stress intensity factor range ε x , ε y = strains in the Cartesian directions ρ = density ν = Poisson's ratio σ 1 , σ 2 = principal stresses σ open = opening stress σ x , σ y = stresses in the Cartesian directions