Dog-bone Type Specimens Research Articles

Evaluation of wall thickness effect on tensile properties of injected short fiber reinforced polymers

The aim of this paper is to analyze the effect of increasing the wall thickness in injection molded short fiber reinforced polymer (SFRP) parts, focusing mainly on tensile strain and tensile strength, as these are the most used characteristics for structural analyses. The phenomena that makes this evaluation of interest has to do with the microstructure of SFRP injection molded parts and how the fibers get oriented along the flow direction at superficial depths with an increasingly less aligned structure down to the mid plane/surface. By increasing the injected part wall thickness the ratio between the thicknesses of highly oriented layers and poorly oriented layers decreases, thus the tensile properties of the material should suffer a decrease as well.In order to study the mentioned hypothesis two types of materials were tested, PPA GF33 and PPS GF40, dog-bone type specimens were cut at different angles to the flow direction from injection molded plates of 2 and 3 mm wall thickness values. The tensile strains were recoded using a video extensometer and material data was calibrated using Digimat MX reverse engineering module and Ansys properties homogenization tool and finite element solver.

Investigation of Young’s Modulus and thermal conductivity of epoxy based composite fiberglass material

In this research work, an investigation was made on the Young’s Modulus and thermal conductivity of fiberglass material reinforced with epoxy resin and hardener gum. Composites are made up with epoxy resin: hardener gum mixture of 10:1 ratio. Dog bone type specimen with end tab samples were prepared in different layers to find the Young’s modulus by center-loaded method and thermal conductivity by Lee’s apparatus method. Experimental results show that the Young’s Modulus increases when increasing the number of layers and amount of epoxy resin and hardener gum mixture apply on it. However, the thermal conductivity depends on the thickness of fiberglass mat reinforced with hardener gum and epoxy resin mixture.

Effect of the large cells on the fatigue properties of closed-cell aluminum alloy foam

The effect of the large cells on the fatigue properties of closed-cell aluminum alloy foam is studied experimentally and numerically. To do this, a parameter termed as characteristic diameter (Dch) is introduced. 44 dog-bone type specimens are tested with MTS fatigue test machine. In addition, the fatigue performances are numerically simulated by using foam models generated with a program given in this paper. In both cases, large scatter in fatigue life is observed. After classifying the foams into different groups based on their Dch, the fatigue life results of foams within the same Dch range show smaller diversity. It indicates that Dch is an effective parameter which can be used to classify the fatigue performance of foam materials. For foams with same relative density, foams with higher Dch are inclined to have shorter fatigue lives, even though the cell size distributions of foams are different. It is concluded that the fatigue life of foam is dominated by the large cells rather than the cell size distribution. By observing the fatigue life contour obtained from numerical simulation, the dangerous regions in the cell structure are found near the cell walls of larger cells and on the outer surfaces of foam.

Annealing optimization for tin–lead eutectic solder by constitutive experiment and simulation

Abstract

Tensile test criterion of transformation-induced elasticity and plasticity alloys for load-displacement measurement

Abstract The tensile test criterion to obtain a reliable stress-strain curve from load-displacement data of metallic materials exhibiting twinning or phase transformation was developed especially for environments that do not allow the use of an extensometer. The study shows that neither ASTM E8 / E8M standard specimen nor strip-shaped specimen geometry was appropriate for converting load-displacement data to an actual stress-strain curve; the former exhibited an undesired two-stage yield, while the latter revealed premature fracture. To solve these problems, the relationship between the specimen geometries and load-displacement data was carefully analyzed for dog-bone type specimens having a minimized fillet radius; it was found that the ratio of grip width W gr to gauge width W ga should be higher than the ratio of fracture stress to the first yield stress σ 1 . Otherwise, a second yield always occurred when the stress reached a value close to σ 1 W gr / W ga , obstructing the data analysis to reconstruct the actual stress-strain curve from load-displacement data. Finally, a methodology to verify whether the tensile test satisfied the criterion was suggested in terms of a nominal strain hardening rate.

Reliability design and assessment of a micro-probe using the results of a tensile test of a beryllium–copper alloy thin film

This paper describes the results of tensile tests for a beryllium–copper (BeCu) alloy thin film and the application of the results to the design of a probe. The copper alloy films were fabricated by electroplating. To obtain the tensile characteristics of the film, the dog-bone type specimen was fabricated by the etching method. The tensile tests were performed with the specimen using a test machine developed by the authors. The BeCu alloy has an elastic modulus of 119 GPa and the 0.2% offset yield and ultimate tensile strengths of 1078 MPa and 1108 MPa, respectively. The design and manufacture of a smaller probe require higher pad density and smaller pad-pitch chips. It should be effective in high-frequency testing. For the design of a new micro-probe, we investigated several design parameters that may cause problems, such as the contact force and life, using the tensile properties and the design of experiment method in conjunction with finite element analysis. The optimal dimensions of the probe were found using the response surface method. The probe with optimal dimensions was manufactured by a precision press process. It was verified that the manufactured probe satisfied the life, the contact force and the over drive through the compression tests and the life tests of the probes.

Measurement of Poisson’s ratio by means of a direct tension test on micron-sized specimens

Abstract A methodology developed for measuring Young’s modulus and the full stress–strain curve on micron-sized specimens was extended here to measure Poisson’s ratio. A dog-bone type specimen was used within a small loading machine with a maximum load of 5 N. The specimen was fabricated from single crystal silicon (SC-Si) with the specimen gage and loading direction in the 〈0 0 1〉 orientation. A silicon on insulator (SOI) wafer was used with a deep reactive ion etching (DRIE) based process. Geometrical parameters of the initial cross-sectional area of the gage were measured by means of image processing on environmental scanning electron microscope (ESEM) images. The test setup also consists of an optical microscope with a monochromatic camera and a data acquisition system. The strains were obtained through the displacement field which was determined by means of digital image correlation (DIC). A speckle pattern was placed on the specimen gage. SC-Si was chosen to study since it is expected that on both the micro and macro-scales, Young’s modulus and Poisson’s ratio will have the same value. Hence, the accuracy of the method may be examined. The average value of Young’s modulus E = 131.4 ± 2.1 GPa was obtained with the micro-specimens and is consistent with values determined on the macro-scale ( E = 130 GPa). The average value of Poisson’s ratio on the micro-scale was found as ν = 0.23 ± 0.03 which is lower than the macro-scale value of ν = 0.28. The failure stress was determined to be σ f = 1.46 ± 0.10 GPa. Results for Young’s modulus reflect the reliability of the methodology which is suitable for characterization of a large variety of materials exploited in micro-devices for both sensing and actuation. The reasons for the low values measured for ν were investigated through emulations of determining the strains. An improvement in the image acquisition system is suggested.

Determination of tensile properties and residual stresses of Ni-Co thin films

This paper reports tensile properties and residual stresses of Ni-Co thin films. To measure elastic (and plastic) properties, direct tensile tests using dog-bone type specimens are performed first. Assuming that residual stresses vary linearly through the film thickness, bending and membrane residual stress components are measured using cantilever beam and T-structure beam specimens, respectively. Averaged values of Young’s modulus, yield strength and tensile strength are found to be about 163GPa, 1,700MPa and 2,000MPa, respectively. The membrane and bending residual stress components are found to be about 825MPa and 47MPa, respectively.

Thermo-mechanical characterisation of AA 6056-T4 and estimation of its material properties using Genetic Algorithm

This paper presents an experimental investigation of thermo-mechanical material properties of AA 6056-T4, which is used extensively in aeronautic applications. Monotonic tensile tests have been carried out on the dog-bone type specimens at temperatures ranging from room temperature (16 °C) to high temperature (450 °C) with two different strain rates; viz. high strain rate (∼0.002 s −1) and low strain rate (∼0.0002 s −1). Specimens were heated with the help of Joule heating system using Gleeble® 3500 machine at a temperature rate of 25 °C/s. Material properties which were investigated include the Young’s modulus, yield strength at 0.1% plastic strain and hardening modulus. Estimation of material properties using Genetic Algorithm is introduced in the second part of the paper. This approach is incorporated to suggest the model for material properties in terms of temperature and strain rate. The suitability of the proposed model is evaluated using experimental data. Having established a reasonable comparison with experimental results, the material properties are predicted with consistent strain rate values.

Size effect on stress–strain relation of neat polyurethane foam

The basic mechanical properties of a structural engineering material are usually obtained by uniaxial tension testing using a dog-bone type specimen and little attention is paid to the size of the specimen or the size of the strain measuring gage. We show that for the neat polyurethane foam material, two different size specimens exhibit a large difference on their mechanical response to load. A unique experimental mechanics technique called the multi-scale speckle method is introduced to obtain the mechanical properties of the specimens. The larger specimens were tested using a tabletop testing machine, while the smaller ones were tested inside the chamber of a scanning electron microscope.

Microstructure and creep behaviour of eutectic SnAg and SnAgCu solders

The paper presents creep data, that was gained on specimens of different microstructures. The three specimen types have been flip chip solder joints, pin trough hole solder joints and standard bulk solder specimens. The bulk solder specimen was a dog-bone type specimen (diameter=3 mm, length=117 mm). The pin trough hole solder joint consisted on a copper wire that was soldered into a hole of a double sided printed circuit board (thickness 1.5 mm). The flip chip solder joint specimen consisted of two silicon chips (4 mm × 4 mm), which were connected by four flip chip joints (one on each corner). SnAg and SnAgCu flip chip bumps (footprint 200 μm × 200 μm, joint height 165–200 μm, centre diameter 90…130 μm) were created by printing solder paste. Constant–load creep tests were carried out on all three specimen types at temperatures between 5 and 70 °C. Creep data was taken for strain rates between 10 −10 and 10 −3 s −1. The specimens were tested in “as cast” condition and after thermal storage. The microstructural properties of the bulk specimens and real solder joints were examined using metallographic sectioning, optical microscopy techniques, and SEM-microprobe analysis. The results of the microstructural analysis were related to the investigated mechanical properties of the solders. Models of SnAg3.5 and SnAg4Cu0.5, that can be used with the ANSYS FEM software package, will be presented.

A study of tension test specimens of laminated hybrid composites. 1: Methods of approach

This paper covers the statistical analysis, stress analysis, and failure characteristics of two types of tension specimens used for testing fiber/metal hybrid laminates. The specimen geometries considered are straight-sided and dogbone-type specimens. Statistical analysis of the results from both specimen types shows that the longitudinal mean tensile ultimate strength is significantly different at the 5% significance level, however, this difference becomes insignificant if the size effect is taken into account. However, the means of the tensile yield strength and tensile modulus are found to be independent of specimen type. Stress analysis of the dogbone-type specimen shows it to be subjected to high shear stresses and tensile stress concentrations which tend to degrade its mechanical performance. Results from both analytical and experimental studies suggest that it is better to use the straight-sided specimen on tension testing for fiber/metal hybrid laminates. Fracture topography of specimens is also investigated and interpreted.