U-shaped Specimens Research Articles

The effect of the riveting process and aging on the mechanical behaviour of an aluminium self-piercing riveted connection

Abstract The joining of two aluminium plates with an aluminium self-piercing rivet, as discussed by Hoang et al. (2010) , showed that heating to soften the plates to be joined might be used to avoid plastic compression or fracture in the rivet. In the present paper, the mechanical behaviour of self-piercing riveted connections using an aluminium rivet was investigated. Two U-shaped specimens in alloy AA6063-W, obtained by a solution heat treatment of the alloy in temper T4, were joined using an aluminium self-pierce rivet in alloy AA7278-T6. The mechanical behaviour of these connections was tested after 3 and 30 days of natural aging of the riveted specimens. Test results showed that the strength of the aluminium riveted joints tended to stabilize after three days of natural aging. In order to evaluate the process effect (i.e. the effect of the pre-straining of the plates in W temper as the result of the riveting process, and the subsequent natural age-hardening of the plates) on the mechanical properties of the riveted connection, a comprehensive material test programme was carried out. Test results revealed that there is an interaction between the pre-straining and natural aging which lowers the material properties in terms of the flow stress compared to the ‘virgin’ material, i.e. the curve obtained after heat treatment and aging only. Then, the process effect on the mechanical behaviour of the riveted connections was investigated more closely by using a 3D-model generated in LS-DYNA. The combined effect of the pre-straining and natural aging was accounted for in the numerical analyses by means of a user-defined constitutive model. Numerical analyses revealed that it is necessary to consider the combined effect of plastic deformation and aging in order to predict the mechanical behaviour with a reasonable accuracy.

Geometric functions of stress intensity factor solutions for spot welds in U-shape specimens

In this paper, the stress intensity factor solutions for spot welds in U-shape specimens are investigated by finite element analyses. Three-dimensional finite element models are developed for U-shape specimens to obtain accurate stress intensity factor solutions. In contrast to the existing investigations of the stress intensity factor solutions based on the finite element analyses, various ratios of the sheet thickness, half specimen width, half specimen length, and corner radius to the nugget radius are considered in this investigation. The computational results confirm the functional dependence on the nugget radius and sheet thickness of Zhang’s analytical solutions. The computational results provide a geometric function in terms of the normalized half specimen width, normalized half specimen length, and normalized corner radius to Zhang’s analytical solutions. The computational results also provide a geometric function in terms of the aspect ratio of the specimen to complete Lin and Pan’s analytical solution. Finally, based on the analytical and computational results, the dimensions of U-shape specimens are suggested.

Effects of Specimen Width and Specimen Length on Stress Intensity Factor Solutions for Spot Welds in U-Shape Specimens

Effects of Specimen Width and Specimen Length on Stress Intensity Factor Solutions for Spot Welds in U-Shape Specimens

Taphonomy and ontogeny of a multibranched Ediacaran fossil: Bradgatia from the Avalon Peninsula of Newfoundland

Rangeomorphs, an extinct group of Ediacaran organisms with a fractal architecture and modular construction, occur abundantly in the Mistaken Point assemblage (575–560 Ma) of the Avalon Peninsula of Newfoundland. Bradgatia is represented by hundreds of specimens, collectively permitting analysis of its morphology, growth mode, and life habits. Bradgatia is a petalage that consists of a radial array of up to eight petals, each exhibiting up to four visible orders of rangeomorph branching. The taphonomy and ontogeny of Bradgatia are tightly linked by a change in preserved morphology, from juvenile I- to V-shaped specimens to larger U-shaped specimens, to the largest and ontogenetically oldest O-shaped specimens. Bradgatia probably maintained a constant number of petals that gradually spread out with age. The number of frondlets per petal does not correlate with length, suggesting either fractal or inflationary growth. Presence of a structure from which petals branch, abundance of contour-parallel specimens, differential preservation within specimens, and specimens overlying spindles and discs all imply that Bradgatia had an attached, epifaunal, suspension-feeding lifestyle. Bradgatia's multiple thin petals would have helped to filter water more efficiently, while its lack of a stem would have allowed for suspension feeding along the entire length of each petal.

On flow properties, fibre distribution, fibre orientation and flexural behaviour of FRC

For improving the mechanical properties of fibre reinforced concrete one can either increase the fibre content, use hybrid fibre systems, or one can attempt to align fibres in the direction of stress. In this paper, it is attempted to use the flow-properties of the fresh (self-compacting) concrete to change the fibre distribution and orientation. Using a single mixture of fibre reinforced concrete, containing 3% of 30 mm long straight steel fibres, the fibre distribution and orientation was determined in three different parts of a ‘U-shaped specimen’ where the concrete could flow in three different directions. The fibre distribution and orientation was determined from a CT-scan. Flexural tests show that the mechanical behaviour depends on the fibre distribution and orientation, which can be affected by changing the viscosity of the fresh mixture.

Shape restoration effect associated with order–disorder transformation in equiatomic AuCu and AuCu–Ga alloys

Shape restoration effects associated with order–disorder transformation in equiatomic AuCu and Au0.47Cu0.47Ga0.06 alloys were examined by means of surface roughness measurements of sheet specimens and the change in the distance between tips of U-shaped specimens. The specimen surface became irregular and a macroscopic shape change occurred after an ageing heat treatment. The shape change was attributed to the heterogeneity in the deformation which arose from the stress release by twinning at the free surface. After disordering of the age-hardened specimen, they regained completely to its original shape. When the specimen was aged without any constraint, spontaneous deformation occurred and did not result in any given shape. However, when the external stress was applied during ordering heat treatment, a given shape was obtained by the formation of favorably oriented ordered domains and twin lamellae. It is suggested that once the direction of deformation was decided, growth of the existing variants continued.

SEM observations on stress corrosion cracking of commercially pure titanium in a topical fluoride solution

Objectives. The purpose of the present study was to determine whether commercially pure titanium is susceptible to stress corrosion cracking/hydrogen embrittlement in a topical fluoride solution used in preventive dentistry. Methods. Thin electropolished titanium test specimens were previously cold-rolled or cold-rolled and annealed before testing. For the stress corrosion tests, the U-shaped specimens of both treatment types were stressed into a radius of curvature of 30 mm. Then, the bent part was placed in the fluoride solution at 37°C for 1, 5, 10, and 20 d. The effects of the fluoride solution on cold-rolled and annealed titanium were studied using a scanning electron microscope. In addition, mechanically fractured surfaces of cold-rolled titanium specimens exposed and not exposed to the fluoride solution were examined by SEM. A qualitative evaluation of the surfaces was conducted. Results. Narrow cracks were observed in cold-rolled specimens following exposure to the fluoride solution for 5 d. The cracks were associated with branching, a characteristic of stress corrosion cracking. The cold-rolled specimen exposed to the fluoride solution exhibited a brittle fracture. In contrast, the fracture mode of the unexposed specimen was ductile in nature. Significance. Topical fluoride solutions can cause stress corrosion cracking of commercially pure titanium.

A new shielding device using U-shaped magnetic material

The authors propose shielding devices constructed with many U-shaped soft magnetic materials. The key feature of these devices is the use of the principle of magnetic shielding based on the vector sum of the external field and the demagnetizing field outside the U-shaped specimen. Shielding effectiveness can be controlled easily by adjusting the demagnetizing factor, which depends on the shape of the specimen. When the demagnetizing field due to the U-shaped specimens cancels the external field perfectly, the shielding factor S (external field/internal field) becomes extremely high (>10/sup 3/). >

A new type of magnetic shield (abstract)

We propose a new type of magnetic shield which is made by piling the many U-shaped soft magnetic materials. We call it ♯-type shield because of its shape as shown in Fig. 1. The principle of magnetic shielding is based on the zero vector sum of the applied field and demagnetizing field outside the soft magnetic specimens. In this way a weak field region is produced inside the ♯-type shield which screen out the external field. Therefore, shielding effectiveness can be controlled by changing the demagnetizing factor which primarily depends on the shape of the specimen. It is hard for the conventional magnetic shield like a cylindrical shell to control its demagnetizing factor, therefore, the shielding effectiveness is based on only the permeability of the soft magnetic materials. However, it is easy for the ♯-type shield to control its demagnetizing factor by changing the length of U-shaped speciments. The shielding ratios S (external field/internal field) of the ♯-type shield have the maximum as the external field increases. The demagnetizing field due to U-shaped iron cancels perfectly the external field when the shielding ratio S is maximum. Therefore, S is extremely high (S=104). The critical field at which S is maximum optionally varies with the length L of U-shaped specimens. The shielding effectiveness of ♯-type shield using iron is as effective as that of the cylindrical shield using permalloy. The ♯-type shield is more economical. The shield is free from temperature rising because of the open structure. The ♯-type shield using iron can be applied to almost any device having magnetic structure or involving electron beam.

Some modifications of electric circuitry for internal friction measurements of U-shape specimens

Some modifications of the electric circuitry are described for the apparatus of the internal friction measurement of thin wire specimens; the apparatus has been developed by Franklin et al. The improved apparatus has been successfully used in the internal friction measurements of cold-worked vanadium specimens.

Effects of Cu, Mo and C on the corrosion of deformed 18Cr8Ni stainless steels in H 2SO 4/NaCl solutions

The effects of Mo, Cu and C on the rate and type of corrosion of 18Cr8Ni stainless steels after deformation into U-shaped specimens have been investigated in 5N H 2SO 4 solutions containing up to 0·4M NaCl at 40°C. General corrosion, intergranular corrosion, and/or transgranular stress-corrosion cracking were found to occur, the type of attack depending on the contents of Mo, Cu and C in the steel, the concentration of NaCl in the solution, and the degree of deformation. In particular, it was observed that carbon has an effect on intergranular corrosion in these solutions, which is quite different from that observed in Strauss and Huey tests.

Low Frequency Corrosion Fatigue of a Carbon Steel with Stress Concentrations

A low speed constant strain type of reverse bend corrosion fatigue machine using U-shaped specimens of rectangular section is described. The air-fatigue and corrosion-jatigue behaviour of a carbon steel at the fixed frequency of 1·7 Hz is reported in specimens tested with and without stress concentrations being present in the form of drilled holes. Measurements of corrosion potential and metallographic details of the fatigue cracks are presented. The possibility of establishing a ‘corrosion factor’ for use in conjunction with the well defined stress concentration factor is examined on the basis of the experimental data derived.