Effect Of Specimen Configuration Research Articles

Effect of specimen configuration and notch root angle on fatigue behavior of novel dissimilar resistance spot welds of AA5754 to HSLA steel

Facing stringent requirements for fuel economy and regulations for greenhouse gas emissions, structural lightweighting using multi-material solutions has become commonplace in the automotive industry. When joining dissimilar materials such as aluminum to steel by resistance spot welding (RSW), a thin layer of brittle intermetallic compound forms at the aluminum-steel interface and dominates mechanical behavior of the joint. In this contribution, RSW of 1.1 mm thick AA5754 sheet to 2.0 mm thick high-strength low-alloy (HSLA) steel sheet was performed using multi-ring domed (MRD) electrodes and multiple solidification weld schedules to achieve acceptable static joint strength. Load-controlled fatigue tests were conducted and the results show that the fatigue life is longer in the AA5754 to HSLA steel spot welds than that of the 1.1 mm thick AA5754 joined to itself (aluminum-aluminum). Structural stress analysis revealed that all fatigue life data points from both the lap shear and coach peel configurations fall onto a single master curve indicating that the weld nugget diameter is the controlling parameter for fatigue life. Finite element simulation considering material inhomogeneity in the weld further confirms that a large notch root angle at the weld nugget is beneficial to yield longer fatigue life as less maximum principal strain occurs in the aluminum sheet in the AA5754-HSLA steel spot welds.

Comparison of Testing Method Effects on Cracking Resistance of Asphalt Concrete Mixtures

As an inherent characteristic of materials, the fracture toughness is an important parameter to study the cracking behavior of asphalt concrete mixtures. Although material compositions and environmental conditions have a significant effect on the fracture toughness, for a certain material and testing environment, the test condition including the specimen configuration and loading type may also affect the obtained fracture toughness. In this paper, the effect of specimen configuration and applied loading type on the measured pure mode-I fracture toughness (KIc) is investigated. In order to achieve this purpose, using a typical asphalt mixture, four different test specimens including Semi-Circular Bend (SCB), Edge Notch Disc Bend (ENDB), Single Edge Notch Beam (SENB) and Edge Notch Diametral Compression (ENDC) disc are tested under pure mode I. The mentioned specimens have different shapes (i.e., full disc, semi-disc and rectangular beam) and are loaded either with symmetric three-point bending or diametral compressive force. The tests were performed at two low temperatures (−5 °C and −25 °C) and it was observed that the critical mode-I fracture toughness (KIc) was changed slightly (up to 10%) by changing the shape of the test specimen (i.e., disc and beam). This reveals that the fracture toughness is not significantly dependent on the shape of the test specimen. However, the type of applied loading has a significant influence on the determined mode I fracture toughness such that the fracture toughness determined by the disc shape specimen loaded by diametral compression (i.e., ENDC) is about 25% less than the KIc value with the same geometry but loaded with the three-point bending (i.e., ENDB) specimen. In addition, the fracture toughness values of all tested samples were increased linearly by decreasing the test temperature such that the fracture toughness ratio (KIc (@−25 °C)/KIc (@−5 °C)) was nearly constant for the ENDB, ENDC, SCB and SENB samples.

Effect of specimen configuration and orthotropy on the Young’s modulus of solid wood obtained from a longitudinal vibration test

Abstract Young’s modulus in the longitudinal direction was measured by a longitudinal vibration (LV) test on western hemlock specimens with various length/width ratios. The effects of the configuration and orthotropy of the specimen on the measurement of Young’s modulus was investigated through subsequent finite element (FE) calculations. The experimental results suggested that Young’s modulus could not be obtained accurately when the length/width ratio of the specimen was in a certain range. The FE calculations revealed that Young’s modulus in the transverse direction and Poisson’s ratio in the length-width plane, as well as the length/width ratio, affected the Young’s modulus value. However, the results showed that when the length/width ratio of the specimen was larger than 10, Young’s modulus could be measured accurately with the LV test with a reduction in the effect of orthotropy.

Effect of specimen configuration on fatigue properties of dissimilar aluminum to steel resistance spot welds

General Motors (GM) has developed a proprietary resistance spot welding process using a Multi-Ring, Domed (MRD) electrode geometry that is capable of producing welds between aluminum alloys and steel materials with acceptable joint strength. This work presents fatigue properties of resistance spot welds (RSWs) produced between dissimilar 1.2-mm thick wrought aluminum AA6022-T4 and 2.0-mm thick IF steel RSWs in tensile-shear and coach-peel configurations. The results were compared to those of spot welds made of 1.2-mm thick and 2.00-mm thick AA6022-T4. The tensile-shear and coach-peel spot welds exhibited limited scatter in fatigue life for both stack-ups. The overall fatigue life of the tensile-shear AA6022-T4 to IF stack-ups was much greater than that of the AA6022-T4 to AA6022-T4 stack-ups. However, in coach-peel, there was no significant difference in fatigue life between the two stack-ups. In both tensile-shear and coach-peel fatigue tests the fracture mode for both stack-ups was primarily crack growth through the 1.2-mm thick AA6022-T4 sheet. The superior performance of the tensile-shear AA6022-T4 to IF steel RSWs was most likely a result of larger weld nugget size along with microstructural features that improved performance. These included more favourable notch root openings as well as columnar grain growth and alloying of the aluminum nugget with iron that could retard fatigue crack propagation.

Do the geometry and aggregates size influence external sulfate attack mechanism?

ESA performance testing protocols are mainly a set of exposure conditions, monitoring strategy, and specimens configuration. Although the large feedback on the representativeness of exposure conditions and the relevance of monitored parameters, the effect of specimen configuration still deserved to be studied. In order to investigate the effect of composition and geometry on ESA degradation progress and performance evaluation, an experimental campaign was conducted in this study. Among the 8 tested specimen configurations, 5 geometries (prismatic, cylindrical and 3 hollow cylindrical geometries) and 3 compositions (concrete, concrete equivalent mortar and standard mortar), the cylindrical mortar specimen was selected as the most adapted configuration, in term of ESA degradation expression, for the adopted performance testing procedure. The different configurations lead to the same overall mechanism of degradation but the geometry and the composition influenced the magnitude of some chemical or physical degradation parameters, due to couplings between chemical and mechanical degradation.

Effects of specimen configuration and measurement method of strain on the characterization of tensile properties of paper

Uniaxial-tension tests of copy paper were conducted to measure the tensile properties, including Young’s modulus, proportional limit stress, and tensile strength in the machine direction (MD) and cross direction (CD) using straight and dog-bone-shaped specimens. In the tests using the straight specimen, the distance between the grips was varied. Additionally, the tensile strain was obtained from the crosshead movement and elongation between the lines photographed by a CCD camera. When using a straight specimen in the MD, the grip distance influenced the Young’s modulus value, and the tensile strength was markedly lower than that of the dog-bone-shaped specimen. In contrast, the tensile properties in the CD could be obtained even when using the straight specimen while reducing the influence of stress concentration at the grip.

Effect of specimen configuration on the measurement of off-axis logarithmic decrement of solid wood measured by longitudinal and flexural vibration tests

Abstract Douglas fir (Pseudotsuga menziesii) lumber was tested in terms of off-axis modulus of elasticity (MOEoff-axis) and off-axis logarithmic decrement (λ off-axis) by longitudinal and flexural vibration (VTlong and VTflex) methods. Similar to the results obtained in a previous study, these results indicate that the values of MOEoff-axis are dependent on the length-to-width ratio of specimens when the value of off-axis angle (θ) is approximately 15°. Although the λ off-axis values are also dependent on the length-to-width ratio, the dependence is not pronounced over a specific range of θ. To measure the λ off-axis value accurately, as well as the MOEoff-axis value, the specimen should be sufficiently slender.

Effect of Specimen Configuration and Lamination Construction on the Measurement of the In-plane Shear Modulus of Plywood Obtained by the Asymmetric Four-point Bending Test

In this study, the in-plane shear modulus of 3-, 5-, and 7-ply lauan wood (Shorea sp.) was measured by conducting an asymmetric four-point bending (AFPB) test with various specimen depth/length ratios and subsequently performing a flexural vibration (FV) test and finite element analysis (FEA). The results obtained from the experiment and the FEA revealed that the in-plane shear modulus was dependent on the depth/length ratio of the specimen. The dependence of the in-plane shear modulus obtained from the AFPB test was more significant than that obtained from the FV test. Additionally, the in-plane shear modulus values obtained from the AFPB test varied more significantly than those obtained from the FV test. In determining the in-plane shear modulus of plywood, the FV test was therefore superior to the AFPB test.

Effect of specimen configuration and ageing time on fracture load of multilayered ceramic disks

Effect of specimen configuration and ageing time on fracture load of multilayered ceramic disks

Evaluation of creep crack growth properties of Gr. 92 steel weldment

High Cr ferritic heat resistant steels are used for boiler components in ultra-super critical thermal power plants. In weld components of these steels, Type-IV creep damages formed in the fine-grained heat-affected zone (HAZ), causing their creep strength to decrease at high temperatures. To assist the standardization of the testing method for creep crack growth in weld components, we conducted round robin tests using ASME Grade 92 steel as part of the VAMAS TWA31 collaboration. The CCG tests were carried out using the CT specimen and the circumferentially notched round bar specimen for both the base metal and weld joint of Gr. 92 steel. The effects of specimen configuration, temperature, load and stress triaxiality conditions on the crack initiation and growth properties were investigated.

Results of a Japanese round robin program for creep crack growth using Gr.92 steel welds

Abstract High-Cr ferritic heat-resistant steels are commonly used for boiler components in ultra-super critical thermal power plants operated at about 600 °C. In the welded joints of these steels, Type-IV cracks initiate in the fine-grained HAZ during long-term use at high temperatures, causing their creep strength to decrease. To assist the standardization of the testing and evaluation method for creep crack growth (CCG) in the welded components, we conducted round robin tests (RRT) using 9Cr–0.5Mo–1.8 W–V–Nb steel (ASME Grade 92 steel) welded joint as part of the VAMAS TWA31 collaboration. The CCG tests were carried out using the CT specimen and the circumferentially-notched round bar specimen for both the base metal and welded joint of Gr.92 steel. Testing was performed at four different laboratories. The effects of specimen configuration, temperature, load, and stress triaxiality conditions on the crack growth rate and fracture life were investigated.

Effect of Specimen Configuration and Loading Types on Fatigue Life of an Annealed 0.42% Carbon Steels

In the present study, a unified crack growth law based on the small fatigue crack growth law was investigated using specimens with different configurations and loading types for the annealed 0.42% carbon steel. Then, a convenient prediction method of fatigue life was proposed. This small fatigue crack growth rate was uniquely determined by the modified small crack growth law, , despite of changing for specimen configurations and loading types. The constants of can be estimated by an empirical equation of without stress/strain gradient. Considered the effect of stress gradient for different specimen configurations and loading types, the stresses under bending loadings and specimen configurations was calculated from that under push-pull loading. Therefore, the fatigue life of the specimens with different configuration and under different loading types can be simply estimated through the fatigue crack growth law based on the only tensile strength of carbon steels. The availability of proposed method was confirmed experimentally by the results of several carbon steels.

Mechanics of Adhesively Bonded Flip-Chip-on-Flex Assemblies. Part I: Durability of Anisotropically Conductive Adhesive Interconnects

This is Part I of a two-part paper on adhesively bonded flip-chip-on-flex (FCOF) microelectronic assemblies. This paper examines the use of anisotropically conductive adhesives (ACAs), and the companion paper (Part II) addresses the use of non-conductive adhesives (NCAs). Two types of FCOF dies, bonded with ACAs, were subjected to temperature cycling and repeated temperature shock durability tests. The specimens have Au-plated bumps and the ACA contains Au-plated polymer particles. Specimens were fabricated with different bonding pressures. Scanning Electron Microscopy (SEM) investigations were performed to characterize the distribution and shape of the conducting particles. Contact resistance measurements, conducted throughout the temperature cycling durability test for 1000 temperature cycles between 20°C and 115°C, showed that resistance varied cyclically with each temperature cycle, but there was no increase in the average resistance over the duration of the test. In contrast, cyclic thermal shock tests between –50°C and 115°C produced failures within 200–2500 cycles, depending on the specimen configuration. Studies were conducted to examine the effect of specimen configuration and temperature on: (i) interconnect resistance, based on electro-thermal modeling; and (ii) mechanical contact stresses, based on thermomechanical modeling. Modeling techniques used detailed finite element analysis (FEA) as well as simpler rapid-assessment models based on 2D variational methods (for example, the Raleigh–Ritz method) and 1D electrical resistance networks. These models were used to parametrically investigate the influence of interconnect design, bonding pressure, temperature and interconnect degradation mechanisms, on the contact resistance and contact stresses. Results suggested that the thermal expansion of the ACA during temperature cycling did not cause any changes in the contact resistance at the contact interface, thus suggesting the possibility of bonding at Au–Au interfaces. During thermal shock, the expansion mismatch stress between the die and Printed Wiring Board (PWB) at the low temperature (–50°C) was probably sufficient to fracture this bond. The issue of gold-to-gold bonding will be addressed in a future paper.

Bonded joints with composite adherends. Part I. Effect of specimen configuration, adhesive thickness, spew fillet and adherend stiffness on fracture

This paper deals with glass-fiber-reinforced vinylester composite laminates manufactured by resin infusion and bonded with an epoxy adhesive. The effect of joint configuration, adhesive layer thickness, defects, humidity, spew fillet, and adherend stiffness were investigated by means of tension tests. Four joint configurations were considered: two configurations representing real aeronautical applications namely, the joggle lap joints (JLJ) and the L-section joints (LSJ) and two configurations representing the most popular standard joints namely, the single lap joint (SLJ) and the double strap joints (DSJ). The SLJ and DSJ show higher ultimate loads and displacements to failure than the JLJ and LSJ. The failure load and displacement were found to decrease dramatically when the adhesive layer thickness was increased or when the joint was aged in a hot-humid environment. Intentionally unbonded area in the middle of the joined area did not seem to affect the joint resistance. The investigation of the spew fillet and adherend stiffness for the JLJ showed that the spew fillet effect depended on both the adherend stiffness and the adhesive ductility. The fracture mechanisms were found to change dramatically. Finally, the effect of adherend stiffness was investigated for the JLJ configuration with adherend laminates having stacking sequences of (±45) n and (0/90) n . Most of the joints made from (0/90) n laminates failed at the adherend joggle knee and all the joints made from (±45) n laminates failed at the interface at lower load.

Effect of Residual Stress on Fatigue Crack Growth Behavior of STS 42 Steel Weldments

The fatigue crack growth behavior in butt-welded joints of STS42 steel was examined using compact type (CT), center-cracked tension (CCT) and single edge cracked (SEC) specimens, and the effects of specimen configuration, thickness, crack orientation and location of weld line in the specimens on the fatigue crack growth rate in the welded joints were examined in connection with welding residual stress.The fatigue crack growth rate in the CCT specimen was similar to or slightly higher than that in the base metal, whereas the crack growth rate in the CT or SEC specimen decreased considerably as compared with that in the CCT specimen, except for the CT specimen with a notch on the weld line. The crack growth rate increased slightly with increasing specimen thickness, regardless of specimen configuration. In the case of the CT specimen with perpendicular crack orientation with respect to the weld line, the crack lengths of the both sides of the specimen surface were often different each other. The side with an advanced crack front corresponded to the backing side with finishing pass. When a crack existed within the region of initial compressive residual stress field, the overall distribution of residual stress did not change appreciably. The effect of welding residual stress on the crack growth rate was the same as that of stress ratio on the growth rate of the base metal. The crack growth rate in the welded joints was correlated with the effective stress intensity factor range, ΔKeffR, which was estimated by superposition of the respective stress intensity factors for the residual stress field and for the applied stress, regardless of specimen configuration and distribution of residual stress in the specimens.

A study on the Instrumented Charpy test.

The Instrumented Charpy test was conducted on U-, V-, and fine notched specimens and a fatigue precracked specimen of A508 C1.3 steel and the effect of specimen configuration, test temperature and loading speed on the dynamic fracture toughness was investigated. Comparing the load-displacement curves of the U-notched and fatigue cracked specimen, the fracture toughness at the onset of crack extension was determined and proved to coincide with the lowest value of the dynamic fracture toughness. The J-integral and R-curve of the fatigue cracked specimen were corrected for crack extension by a proposed direct calculation procedure in place of ASTM's step-by-step one.

Effects of Specimen Configuration and Test Frequency on Fatigue Strength

Effects of Specimen Configuration and Test Frequency on Fatigue Strength

The Effect of Specimen Configuration on the Periodicity of a Lattice Image

One of the most controversial issues in the application of the lattice fringe imaging technique concerns the interpretation of the local fringe spacing. It is well-known from the work of Hashimoto et. al. that the specimen configuration may cause the fringe spacings in an image to deviate from the true interplanar spacings of the crystal. Their paper qualitatively described the effects on fringe spacings of variations in specimen thickness, t, and deviation from the Bragg condition, s, and illustrated their results with the first experimental fringe images of Menter. In this paper an explicit formula for spacings in a fringe image is presented and applied to various specimen configurations and materials currently being studied by high resolution techniques which have much closer lattice spacings (∼2 Å) than have previously been considered.

The Effects of Specimen Configuration and Plate Thickness on Large Scale Yielding Brittle Fracture Toughness

In the previous report, it was investigated to evaluate the thickness effects on brittle fracture toughness of mild steel (SS 41) accompained by large scale plastic deformation ahead of crack tip in the three-point bend tests, which satisfied all aspect of British Standard DD 19.It was showed that the critical COD, Φ0C value, was dependent on the plate thickness of specimen, and the effects of specimen configuation and ligament length on the Φ0C value were not yet argued.The object of the investigation is to find the variation of Φ0C value to the specimen configuration and plate thickness. Two types of specimen, i. e., the three-point bend specimen and the compact tension specimen, of which geometries satisfied BS DD 19 and ASTM E 399 except for the plate thickness, are used in the tests.And the authors present a modification of β-value proposed in the previous report, so that the value may be applied to the evaluation of the effects of plate thickness on the displacement and mouth COD in the specimen.The following conclusions are obtained : (1) The Φ0C value at which the brittle fracture occurs is dependent on the specimen thickness, and the other dimensions of specimen hardly contribute to Φ0C value.(2) The thickness effects on brittle fracture toughness should be treated as three dimensional problems, but can be dealt approximately as one of two dimensional problems using the Finite Element Method incorporated the modified β.