Introducing Residual Stresses on Sheet Metals by Slide Hardening under Stress Superposition

The fatigue strength and product life of the components can be improved by introducing compressive residual stresses using mechanical surface treatment. Appling stress superposition is an option to be used in metal forming to reduce the process force. In this work experimental investigations to analyze the influence of stress superposition on residual stresses of sheet metal parts by a slide hardening process were carried out. The flat and elastically pre-bended specimens (i.e. stress-superimposed specimen) were processed with a slide diamond tool under different loading forces. The residual stress generated through the thickness of the sheet metal was similar for the flat and the pre-bended specimens. The superimposed stress by elastic bending of the sheet metal led to higher compressive residual stress compared to the flat specimen under the same loading force. Nevertheless, the contour of the pre-bended specimen showed more bulking compared to the flat specimen. The mechanical characteristics determined by hardness measurements showed no significant improvement when applying stress superposition.

Structural integrity of shot peened Ti6Al4V specimens under fretting fatigue

In the present paper, an experimental campaign performed on shot peened Ti6Al4V specimens under fretting fatigue, available in the literature, is simulated by using the Carpinteri et al. criterion. The experiments examined were carried out using a standard configuration, that is, a cylinder against a flat specimen. The fretting loading is a combination of low-cycle fatigue and high-cycle fatigue, and the corresponding stress field is determined by a FE analysis. A theoretical law is applied to describe the relaxed residual stress produced by shot peening treatment and fatigue loading.

An innovative fixture for testing the crashworthiness of composite materials

Despite the growing diffusion of composite materials in automotive and aerospace sectors, a standard procedure for testing their crashworthiness has not been developed yet. At present, the international standards for testing composite materials under impact conditions are not adequate to test their crush behavior. In this paper, a procedure for measuring the energy absorption due to the compressive crushing of a composite flat specimen, along its mid plane, is proposed. The experimental setup requires a fixture to hold the specimen and to avoid its buckling and an instrumented drop weight tower to obtain the force-displacement curves with the aim of calculating the Specific Energy Absorption. The paper will describe the adopted test procedure and some of the features of the newly developed experimental setup. The effectiveness of the procedure is demonstrated by testing several glass fiber-epoxy specimens under different impact energies.

A new parafocusing paradigm for X-ray diffraction

A new approach to parafocusing X-ray diffraction implemented with an annular incident beam is demonstrated for the first time. The method exploits an elliptical specimen path on a flat sample to produce relatively high intensity maxima that can be measured with a point detector. It is shown that the flat-specimen approximation tolerated by conventional Bragg–Brentano geometries is not required. A theoretical framework, simulations and experimental results for both angular- and energy-dispersive measurement modes are presented and the scattering signatures compared with data obtained with a conventional pencil-beam arrangement.

Динамика полосы Людерса и разрушение алюминий-магниевого сплава, инициированные концентратором напряжений

Spatio-temporal localization of deformation and the rupture of the aluminum-magnesium AlMg6 alloy, initiated by a geometrical stress concentrator, are studied in situ by video recording at a speed of 500 to 20000 frames/s. It is established that a stress concentrator in the form of a small notch with a depth about 1% of the width of a flat specimen is an attractor of bands of macrolocalized plastic deformation, starting from a Lüders band and ending with the start of the main crack. The key role of intersecting deformation macrobands in the development of the main crack is revealed. Possible micromechanisms of viscous destruction associated with the dynamics of the intersection of deformation bands are discussed.

Development of a test method for evaluating the crushing behaviour of unidirectional laminates

More fundamental test methods are needed to assist the development of physically based and truly predictive simulation tools for composite materials under crash conditions. In this paper, a unidirectional flat specimen that can be used to validate the predicted behaviour from a simulation to the physical behaviour in the experiment is developed. A systematic experimental investigation is conducted to evaluate the influence of the trigger geometry on the crushing response by selecting two trigger types and different trigger angles. For longitudinal crushing, the traditional bevel trigger leads to out-of-plane failure by splaying with a limited amount of in-plane fracture, while the proposed trigger achieves a high amount of compressive fragmentation failure. For transverse crushing, the symmetry of the proposed new trigger improves the specimen stability during the crushing process. It is also observed that the weft threads of the unidirectional fabric reinforcement used for the tests have a strong influence on the longitudinal crushing response. The boundary conditions of the test and the information on the specimen failure gleaned from video recordings and microscopic inspections are discussed in order to facilitate a future correlation with modelling results.

Hardness characterisation of grey cast iron and its tribological performance in a contact lubricated with soybean oil

The effect of hardness of grey cast iron flat specimen on its wear and friction on the contact were characterised with the presence of vegetable oil as biolubricant. Prior to the tribological test, the as-received grey cast iron flat specimen hardness was characterised. Friction and wear tests were then conducted using a ball-on-flat reciprocating sliding contact. The one-way analysis of variance (ANOVA) was used to determine the significance of friction and wear data with a 95% significance level. The wear scars after the test were then characterised by surface roughness and wear mechanism. The microstructure and elemental analysis were also reported. The average value of hardness was 210 HV with a large difference between minimum (185 HV) and maximum (250 HV) values. The friction and wear performance of grey cast iron specimens with soybean oil varied with its hardness. The specimens with higher hardness gave lower friction coefficient and greater wear resistance than the lower hardness specimens. The difference in coefficient of friction produced between high hardness specimens (COF = 0.122) and low hardness specimens (COF = 0.140) was 17%. In terms of mass loss, the low hardness specimens (mass loss = 50.38 mg) and the high hardness specimens (mass loss = 12.90 mg) produced a difference of 74%. It is shown that, with soybean oil lubricant, the grey cast iron specimen can produce wide range of tribological data especially on mass loss due to its hardness distribution. The influence of soybean oil lubrication in this work is less in improving the wear resistance (about 7%), but greater for friction reduction (about 24%) compared to an unlubricated grey cast iron surface. The hardness of grey cast iron specimen is an important parameter that needs to be specifically measured and controlled on the contact due to wide hardness distribution of grey cast iron may produce variation in tribological data.

Experimental Measurement of Stress Distribution

The main purpose of this paper is to made experimental stress analysis of flat specimen. Specimens were cycles with constant amplitude loaded in order to maintain adiabatic conditions. Whole loading process of specimens was recorded by infrared camera with high sensitivity. Subsequently values of stress were according to equations for thermoelastic analysis evaluated on the face of specimens. Evaluate values of stress are equal to the sum of the principal stresses thus it is the first stress invariant.