Test Specimen Size Research Articles

Characterization Approach for Compression Molded Discontinuous Fiber Thermoplastic Composites

Thermoplastic composites show potential in increasing the manufacturing production rate of composite aerospace structures. This is largely due to their ability to be consolidated quickly using automated processes. A variety of reinforced thermoplastic material forms are offered that can be processed multiple ways in order to meet structural performance requirements at the necessary production volumes without substantial compromise. Intrinsically, this requires generating a significant amount of statistically-based material property data for each unique material and process combination. Currently, the National Institute for Aviation Research (NIAR) and the Federal Aviation Administration (FAA) are developing a material qualification framework for compression molded discontinuous fiber thermoplastic composites in consensus with industry experts. To aid in the development of the qualification framework, a screening test matrix was formed to identify the key processing parameters and evaluate the appropriate test methods and specimen sizes. Three main variables were considered in the trial testing: reinforcement size, material flow behavior and panel thickness. The effect of these key processing parameters on the mechanical properties are discussed along with guidelines for testing and characterization.

The Effect of Specimen Size on Acoustic Emission Parameters and Approximate Position of Defects Obtained during Destructive Testing of Cementitious and Alkali-Activated Degraded Fine-Grained Materials.

Two sizes of test samples were selected to investigate the effect of size on the level of degradation. The smaller test specimens had dimensions of 40 × 40 × 160 mm, and the larger ones had dimensions of 100 × 100 × 400 mm. Both sizes of test specimens were always made of the same mortar. In one case, Blast Furnace Cement was chosen as the binder. In the other case, it was an alkali-activated material as a possibly more environmentally economical substitute. Both types of material were deposited in three degrading solutions: magnesium sulphate, ammonium nitrate and acetic acid. The reference set was stored in a water bath. After six months in the degradation solutions, a static elastic modulus was determined for the specimens during this test, and the acoustic emission was measured. Acoustic emission parameters were evaluated: the number of hits, the amplitude magnitude and a slope from the amplitude magnitude versus time (this slope should correspond to the Kaiser effect). For most of the parameters studied, the size effect was more evident for the more degraded specimens, i.e., those placed in aggressive solutions. The approximate location of emerging defects was also determined using linear localisation for smaller specimens where the degradation effect was more significant. In more aggressive environments (acetic acid, ammonium nitrate), the higher resistance of materials based on alkaline-activated slag was more evident, even in the case of larger test bodies. The experiments show that the acoustic emission results agree with the results of the static modulus of elasticity.

Study on the load-end shortening formulae of structural elements including hard corner element considering collapse modes based on test and numerical modelling

This paper focus on improving the load-end shortening formulae of structural elements considering collapse modes and steel grades through experimental and numerical methods. The existing load-end shortening formulae in CSR-H is derived from the buckling theoretical formulae of plates and stiffeners. Stiffener elements deform in different collapse modes under compressive loads, while hard corner elements are assumed as elasto-plastic behaviours, which may obviously overestimate the ultimate load carrying capacity due to the local buckling of plates. Beam–column buckling, torsional buckling and web local buckling for stiffener elements and hard corner elements were designed with different sizes of test specimens in compression tests. After compassion, the minimum and appropriate modelling technology with three stiffener elements and four hard corner elements were proposed to verify the load-end shortening curves of structural elements. A new load-end shortening curve for hard corner elements was developed to calculate the ultimate strength, which could reflect the realistic progressive collapse behaviours under longitudinal compression.

Pengaruh Variasi Waktu Gesek Pada Pengelasan Gesek (Friction Welding) Terhadap Kekuatan Impak Baja AISI 1045 Dengan Stainless Steel

The Friction Welding method is a welding method that utilizes heat energy caused by the friction of the two materials to be joined, the heat from the friction will cause the material to become semisolid or plastic. The purpose of this research was to determine the effect of variations in friction time and distance suppression carried out on impact strength and hardness tests using the Friction Welding method on AISI 1045 steel material connected to Stainless Steel 304. The method used is the Response Surface Method (RSM) to determine impact strength value of AISI 1045 steel which is connected to Stainless Steel 304 after the friction welding process is carried out. The variation used in this study is the variation of the pressure distance and friction time. The size of the impact test specimen is made according to the impact test standard, namely ASTM E23. The greatest impact test results were found in specimen number 6 with a pressing distance of 4.41 mm and a friction time of 5 minutes, namely 0.156 Joule/mm2. While the lowest impact value is found in specimen number 1 with a pressing distance of 2 mm and a friction time of 4 minutes, namely 0.038 Joule/mm2.

Bending Strength of Apus Bamboo Fiber Reinforced Asphalt Composite Materials as Small Ship

Bamboo is generally widely used as a material or construction material in homes. However, the use of bamboo as a raw material for shipbuilding is not yet available. To make bamboo as a material in shipbuilding, the bamboo is assembled or made into a composite to meet class standards as a material for shipbuilding. In this study, the composites used were apus bamboo fiber and asphalt. The method of making the composite uses the hand lay-up method with variations of 1 layer of reinforcement, 3 layers of reinforcement, and 5 layers of reinforcement. The dimensions of the test specimen size refer to ASTM D 790-3 which is then carried out by bending tests to determine the strength of the material due to loading and the elasticity of the material. Furthermore, the results of the bending test will be analyzed using the Anova method and compared with the standard material class in ship construction. Results Asphalt composite material with apus bamboo fiber has the highest bending test value of 27,068 Mpa and the lowest bending test value of 25,998 Mpa. Based on these results, it is stated that the Bamboo reinforced asphalt (BRA) material has not been able to match and even exceed the Bamboo reinforced plastic (BRP) material in the woven, non-woven and random fiber variants. It is influenced by the diameter, and the strength of the shape between the fiber and the matrix.

Physics-Based Shear-Strength Degradation Model of Stud Connector with the Fatigue Cumulative Damage

In the whole lifetime of structures, fatigue damage accumulation will exist in the shear connector of steel–concrete composite beams. It is essential to determine the residual mechanical properties of shear connectors under long-term fatigue loads, e.g., the vehicle load on bridges. In this regard, a shear-strength degradation model is proposed for shear connectors. The Bayes theorem is used to develop posterior estimates of the unknown parameters in the degradation model based on the collected pushout test data of pre-damaged stud connectors caused by high-cycle fatigue loads. In addition, according to the proposed shear-strength degradation model, the service reliability assessment is performed with a composite bridge beam. The results indicate that (1) There is a large diversion in the traditional strength degradation model under the action of fatigue cumulative damage. More importantly, this proposed physics-based degradation model can effectively reduce uncertainty. (2) The effects of steel type and test specimen size can be well considered in the proposed shear-strength degradation model, which is beneficial for improving the reliability of risk assessment for fatigued bridges.

A Critical Review on Assessment of Self Healing Performance of Bioconcrete

Bio concrete has been researched a lot worldwide in recent years by several researchers. Even though the concept of different self-healing strategies is not the same but the outcome is the same; to heal the cracks that occur in concrete and recover its strength and durability. Bio concrete contains spores that become active and precipitate calcite in the presence of oxygen and nutrients. As a consequence, the cracks get filled with calcite and seals the crack partially or completely. There are experimental techniques to examine self-healing efficiency in cement mortar and concrete. Experiments like the rate of water penetration and UPV are frequently used in research by several research groups. The test methodologies, protocols, specimen sizes, and shapes may differ according to the healing agent and property to be checked. Different research groups developed their own testing protocols to examine healing efficiency. The current paper made a critical review on self healing assessement with a variety of test procedures that has been used by several researchers from the invention of bio concrete till now. The methodologies are mainly to examine the viability of bacteria inside concrete, identification of calcite precipitated by bacteria, regained strength and durability after healing.

Miniature Beryllium Split-Hopkinson Pressure Bars for Extending the Range of Achievable Strain-Rates

Conventional Split Hopkinson Pressure Bars (SHPB) or “Kolsky” bars are often used for determining the high-rate compressive yield and failure strength of materials. However, for experiments generating very high strain-rates (>103/s) miniaturization of the setup is often required for minimizing the effects of elastic wave dispersion in order to enable the inference of decreasingly short loading events from the data. Miniature aluminum and steel bars are often sufficient for meeting these requirements. However, for high enough strain-rates, miniaturization of steel or aluminum Kolsky bars may require prohibitively small diameter bars and test specimens that could become inappropriate for inferring representative properties of materials with large grain size relative to the test specimen size. The use of a beryllium Kolsky bar setup is expected to enable high rates to be accessible with larger diameter bars/specimen combinations due to the inherent physical properties of beryllium, which are expected to minimize the effects of elastic wave dispersion. For this reason, a series of beryllium Kolsky bars have been developed, and, in this paper, the dispersion characteristics of these bars are measured and compare the data with those of similarly sized 7075-T6 aluminum and C350 maraging steel. The results, which agree well with the theory, show no appreciable frequency dependence of the elastic wavespeed in the data from the beryllium bars, demonstrating its advantage over aluminum and steel in application to Kolsky bars.

Experimental study on the verification of adequate fatigue test specimen size of U‐rib‐to‐deck joints in orthotropic steel bridge decks

AbstractIn this study, the distribution of residual stress of the substructure model and small coupon specimens in orthotropic steel bridge structures is experimentally and numerically investigated to validate adequate specimen sizes. Blind‐hole drilling and X‐ray diffraction methods are used to capture longitudinal and transverse residual stresses and evaluate the effects of the cutting process. The maximum LRS and TRS were reduced by 16.6% and 15.6% from those that existed before cutting, verifying the proper size of small voucher specimens. The width‐to‐thickness ratio of 6–6.25 of small coupon specimens has proven sufficient to capture the effects of stress triaxiality induced by the residual stress. In the spirit of master S‐N curves in ASME standard, the role of residual stress was represented in the fatigue process and does not be additionally taken into account when predicting the fatigue performances of welded structures using prediction methods based on the S‐N curves.

Enhancing bending buckling strength of hollow tubes using concrete filling

Hollow tubular components are widely used in industries as structural elements which are subjected to bending loads. These tubes are susceptible to bending (transverse) buckling, more so in tubes with thinner cross sections. The presented work investigates the effect of adding an inexpensive core like concrete (with good compressive strength) on the bending buckling strength of thin hollow tubes. This study is based on the results obtained from three-point bend tests performed on hollow and concrete filled thin stainless-steel tubes of small diameter. The size of test specimens was chosen such that the bending buckling mode dominates over the yielding as a failure mode. The experimental results are validated by finite element-based simulations. It was observed that addition of a concrete core significantly improves the bending buckling strength of the thin hollow tubes.

Influence of Test Specimen Geometry and Water Soaking on the In Vitro Cytotoxicity of Orthocryl®, Orthocryl® LC, Loctite® EA 9483 and Polypropylene

Depending on their composition, plastics have a cytotoxic potential that needs to be evaluated before they are used in dentistry, e.g., as orthodontic removable appliances. Relevant guidelines set out requirements that a potential new resin in the medical field must meet, with a wide scope for experimental design. In the present study, test specimens of different geometries consisting of varying polymers (Orthocryl®, Orthocryl® LC, Loctite® EA 9483, Polypropylene) were soaked for different periods of time, then transferred to cell culture medium for 24 h, which was subsequently used for 24-h cultivation of A549 cells, followed by cytotoxicity assays (WST-1, Annexin V-FITC-propidium iodide (PI) flow cytometry). In this context, a reduction in the cytotoxic effect of the eluates of test specimens prepared from Orthocryl® LC and Loctite® EA 9483 was particularly evident in the Annexin V-FITC-PI assay when the soaking time was extended to 48 h and 168 h, respectively. Consistent with this, a reduced release of potentially toxic monomers into the cell culture medium, as measured by gas chromatography-mass spectrometry, was observed when the prior soaking time of test specimens of all geometries was extended. Remarkably, a significant increase in cytotoxic effect was observed in the WST-1 assay, which was accompanied by a higher release of monomers when the thickness of the test sample was increased from 0.5 to 1.0 mm, although an elution volume adapted to the surface area was used. However, further increasing the thickness to 3.0 mm did not lead to an increase in the observed cytotoxicity or monomer release. Test specimens made of polypropylene showed no toxicity under all test specimen sizes and soaking time conditions. Overall, it is recommended to perform toxicity studies of test specimens using different geometries and soaking times. Thereby, the influence of the different specimen thicknesses should also be considered. Finally, an extension of the test protocols proposed in ISO 10993-5:2009 should be considered, e.g., by flow cytometry or monomer analysis as well as fixed soaking times.

Data‐driven approach to construct a fracture toughness master curve for ferritic steels based on tensile properties

Data‐driven approach to construct a fracture toughness master curve for ferritic steels based on tensile properties

Influence of weld porosity on crack size estimations in Single Edge Notched Tension (SENT) testing of steels: A numerical study

The acceptance of weld volumetric imperfections such as porosity from the perspective of structural integrity is guided by workmanship criteria. However, there is a lack of knowledge on how and to what extent volumetric imperfections can affect the outcome of fracture toughness tests. The small size of laboratory test specimens potentializes the relative impact of such imperfections. This study numerically investigates the influence of porosity on two crack sizing techniques commonly applied to single specimen fracture toughness testing, namely Unloading Compliance (UC) and Direct Current Potential Drop (DCPD). The investigation focuses on Single Edge Notched Tension (SENT) specimens, commonly used to characterize fracture behavior in low crack tip constraint conditions. An extensive finite element parametric study was performed where single pores and random porosity distributions were generated by element deletion. The results show that both UC and DCPD crack size estimations are influenced by pores of sizes within workmanship criteria acceptable limits, which in some cases might induce (or contribute to) crack size errors superior to validity limits set by fracture toughness test standards.

Evaluation of frost damage on high-belite cement concrete based on Vickers hardness and ultrasonic theory

High-belite cement (HBC) is increasingly used in hydraulic concrete, of which the frost resistance is an important index in cold climatic areas. In the present study, the mass loss, dynamic modulus, cube compressive strength, micro-morphology and pore characteristic parameters of HBC concrete and reference specimens were investigated under freezing and thawing, and their internal frost damages were quantified by micro-Vickers hardness and ultrasonic theory. Test results showed that the frost resistance of HBC concrete was similar to that of ordinary Portland cement (OPC) concrete under the same proportioning, and that their freeze–thaw failure was a continuous and asynchronous process of both surface-to-interior damage and overall deterioration caused by the test mechanism and specimen size. Service life of concrete could be calculated through the thickness of the damaged layer obtained by ultrasonic theory, and models of Vickers hardness distribution and compressive strength prediction based on equivalent Vickers hardness were proposed to evaluate the performance of frozen concrete with high accuracy. This potentially provides a better understanding of freeze–thaw damage and a reference for the popularisation and application of HBC concrete.

A constraint correction method based on use of a single test specimen

Commonly, fracture toughness tests on deeply cracked specimens are used to assess defects in large-scale components. The paper presents a method for selection of test specimen type, size and crack length in order to obtain fracture toughness estimates relevant to defects in cracked pipes. The method uses available closed-form T-stress, stress intensity factor and limit load solutions to determine the required specimen dimensions. The paper reports elastic–plastic finite element analyses for single edge notched bend (SENB) and single edge notched tension (SENT) specimens and cracked pipes which demonstrate good agreement of the matching approach, although care is needed in selecting the appropriate limit load solution for SENT geometries.

Effect of Specimen Geometry on Selected Physical and Mechanical Properties of Epoxy-Based Building Materials

The paper deals with problematics of the influence of size and shape of test specimens prepared according to the valid standard procedures in comparison to specimens prepared according to the standards used for different types of materials (grouts, coatings). The aim of this paper is to verify the possibility of using non-standard specimen sizes to reduce the economic demands of the development of building materials. The issue is tested on the polymer composites prepared in three different amounts of the filler. The polymer composite based on epoxy resin serves as a representative and homogenous material which achieves the same results under various curing temperatures and humidity. The porous structure of prepared samples was also studied and its effect on the selected mechanical properties was observed. It was shown that the specimen shape and size had impact on the mechanical properties of epoxy-based composites.

Influence of specimen diameter size on the deformation behavior and short-term strength range of an aluminum alloy

Abstract Components often manifest varied local behavior due to their manufacturing process. In order to be able to determine local material behavior in the best possible way, it is necessary to take specimens from the area under investigation. Due to constant developments in efficiency and lightweight construction, it is difficult to produce standard-compliant specimens from the examined area in a component. For this reason, specimens with smaller dimensions are often taken. Through the investigation of the influence of size in the area of high-cycle fatigue, it is well known that the size of a test specimen influences its lifespan. Not so much is known about the influence of specimen size on the behavior of material in the field of low-cycle fatigue (LCF). In this work, tensile, LCF and thermomechanical fatigue tests are performed using AlCu4PbMgMn with varied specimen geometries, the smallest test diameter being 3 mm, the largest 7.5 mm. The results of the tensile test show that the mean values of tensile strength for both diameters is within one percent. At LCF load and thermomechanical load, there are no or only slight deviations in deformation behavior. The low cycle fatigue behavior at RT is identical for both diameters. However, the results show that stress-strain behavior is the same for both test diameters, and fatigue behavior is the same, except in tests with high strain amplitudes and temperature.

Fracture resistance study for hot mix asphalt mixture under out of plane sliding mode

Cracked pavements can be subjected to out-of-plane sliding or mode III deformation due to movement of vehicles. In order to design suitable asphalt mixture for manufacturing high resistance pavements against mode III failure, it is necessary to determine a characteristic parameter called mode III fracture toughness (KIIIc) for these materials. In this research a comprehensive experimental study is performed to obtain the value of (KIIIc) for hot mix asphalt (HMA) mixtures under different geometrical and testing conditions. An edge notch disc bend specimen was utilized for conducting the mode III fracture toughness experiments on HMA mixture at low temperature conditions. Several discs with three thicknesses were cut from HMA mixtures made by gyratory compactor machine and with different air voids. The experiments showed that by increasing the size of test specimen, mode III fracture toughness can increase significantly. Furthermore, KIIIc value is increased by decreasing the test temperature from 0 °C to −24 °C and decreasing the air void content from 7% to 3%. A regression analysis was implemented on the test results and it was found that the thickness and air void have the maximum and minimum influences on KIIIc value, respectively. In addition, it was shown that the mode III fracture toughness of tested asphalt mixture is noticeably less than the corresponding value of the same mixture tested under mode I condition with the same testing conditions. The fracture toughness ratio (KIIIc/KIc) that was varied from 0.5 to 0.7 for different testing conditions and specimen sizes was predicted theoretically using some stress/strain based fracture criteria.

Experimental reexamination of transverse tensile strength for IM7/8552 tape-laminate composites

Due to the observed dependence of transverse-tensile strength, Y T, on test geometry and specimen size, there is no consensus regarding a test method that can uniquely measure Y T. This study reexamines the characterization of Y T by comparing results from established flexure tests with results from a new tensile test that exhibits consistent failure in the gage region. Additionally, the effects of surface preparation and direction of transverse fracture are investigated. Results show that Y T is inversely proportional to specimen volume and surface roughness and is insensitive to direction of transverse fracture. The relationship between specimen volume and Y T is adequately captured by Weibull strength-scaling theory, except at the tails of the Y T distributions. However, specimens exhibited microcracking prior to failure, which violates the “weak-link” assumption of the Weibull theory. These findings highlight the challenges of using deterministic Y T values in progressive damage analysis.

Standardization of the method of magnetostriction measurement of grain-oriented electrical steel strip and sheet

Standardization of the method of measurement of AC magnetostriction characteristics of grain-oriented electrical steel strip and sheet by means of a single sheet tester and an optical sensor, i.e. IEC 60404-17 Ed.1 [1], has been promoted in the IEC/TC68/WG2 to meet the demand of transformer industry. The relationship between the magnetostriction characteristics of grain-oriented electrical steel and transformer noise is complicated and yet not fully understood. One of basic problems has been the lack of a standard for the magnetostriction measurements. The measurement requires detection of slight vibration of the test specimen at a resolution of 0.01 μm/m or better. In order to ensure this resolution, not only magnetic aspects but also mechanical aspects of the test apparatus, e.g. the influence of friction and external vibrations, have to be specified. The size of test specimen is restricted to 100 mm × 500 mm. The flux closer is a vertical single yoke or a horizontal double yoke. In order to avoid the influence of friction and vibration, no weight is put on the test specimen except an optical target and a clamp to fix the test specimen to the test apparatus. Also, no weight is connected to the end of test specimen to prevent additional vibration modes. The optical target is low mass and made of non-magnetic and non-conductive materials. The optical target and the clamp are placed between opposite pole faces of the yoke. In order to realize a low and constant friction coefficient, an insertion sheet with a thin fluorine resin-impregnated glass cloth adhesive film on its upper surface is placed under the test specimen. A round robin comparison using different test setups in accordance with the draft of standard was carried out.