End Of Specimen Research Articles

Experimental investigation of mechanical and fracture behaviour of casted alumina (AA6061-SiC-flyash) metal matrix composites

Metal matrix composites (MMC’s) are most voluminously used in defense, automobile and many other engineering-based applications as a substitute for wide elemental range. High durability in combination with excellent corrosive, fire and radiation resistance are the highlighting benefits of the MMC’s. The present experimental study, investigates the effect of %wt variation of SiC (Silicon carbide), Fly-ash (FA) i.e. 5, 10 and 15 %wt and AA6061 on mechanical and fractural properties of alumina MMC’s. Mechanical properties are improved with addition of %wt of FA and with constant %wt of SiC in the alumina matrix. Besides, high amount of impact energy i.e. 86 J was observed at 15% wt SiC and 10 %wt FA. All the fabricated alumina specimens showed smooth and bright fracture surfaces on the failure ends of the tensile specimens confirming brittle mode of fracture formed due to the variation of stress thereby leading to formation of rapid propagation of crack in the direction of stress.

Development of constitutive equations identifying methodology for steels for plastic moulding by compression testing

The influence of frictional coefficient on the cylindrical plastic steel specimen under compression is analyzed. The considered methodology allows determining effective stress dependence on effective strains by compression testing. It is found that the reason for the barrel-shaped plastic steel compressive test specimen form is only friction between contact surfaces of tested specimens and supports. The standard methodology suggests using various friction reduction technologies to reduce the friction effect on stress-strain diagram determination. These can be special lubricants or changes in the shape of the specimen bearing surfaces. But all approaches to the issue with stress-strain diagram determination are unable to be implemented under temperatures above 300°C due to not being able to use lubricants. The plastic steel compression process experiment behind the model with varying only friction coefficients is suggested in order to determine the effect of friction coefficient on the shape of a compressed specimen. This approach makes it possible to search into the effect of friction coefficient and compare the results with a full-scale experiment. The plastic steel compression diagram, having been obtained from a full-scale experiment, permits to determine effective stress-strain relationship, which, in turn, allows calculating the constitutive equation coefficients of the material model necessary for carrying out simulations of plastic steels deformation under both room indoor temperature and temperatures up to 900°C, including the plastic deformation influence. The proposed methodology also provides the possibility to obtain an effective stress-strain relationship and varying the friction coefficient between the specimen end surface and the supports being exposed to elevated temperatures, which cannot be treated by standard test methods. It is shown that the initial data for obtaining the effective stress-strain relationship are the difference in specimen diameters and the force-displacement diagram.

Non-linear distributions of bond-slip behavior in concrete-filled steel tubes by the acoustic emission technique

This study aims to investigate the non-linear distribution of bond-slip behavior in steel-concrete interface of concrete-filled steel tubes (CFST). An analytical model was proposed to account for the attenuation effect in boundaries of load transfer. In this analysis, a modified governing equation with the second-order ordinary differential form was deduced on the basis of elastic theory. Solutions of slippage, bond stress and potential energy in the steel-concrete interface were then obtained. For the model validation, measurements of acoustic emission (AE), as well as strain gauge, were performed in a push-out test of CFST. Test results agree well with the solutions of the analytical model proposed. The interfacial bond stress exhibits a highly non-linear distribution along the direction of load transfer. The maximum stress appears nearby the position of 0.2L away from the specimen end, and is about 1.2 times of the average shear strength in steel-concrete interface. In addition, the AE peak frequencies of bond failure have two main bands, including 75–125 kHz and 290–340 kHz. It indicates that there are mainly two failure modes during the debonding of steel–concrete interface in CFST.

A New Direct Tension Test Method for Soils and Soft Rocks

Abstract Tensile strength plays a crucial role in many engineering activities involving soils and soft rocks. Currently, several methods for tensile strength determination exist, the most common of which include the direct tension method, Brazilian test, ring test, axial fracturing test, bending test, and hydraulic fracturing test. However, outstanding problems associated with these methods, e.g., undesirable eccentric forces and damage of specimen ends, significantly affect obtained tensile strength values. To overcome these problems, we propose an alternative direct tension test method together with the newly developed apparatus. The proposed method uses an annular specimen that is tension-loaded on the inner hole. The method was evaluated through a series of tests on undisturbed soil and remolded gypsum-sand mixture specimens. For validation, comparison of results between the proposed method and the International Society for Rock Mechanics (ISRM)-suggested method was performed. Based on the results of the experimental program, the proposed method is considered more capable of and more suitable for determining the tensile strength of soils and soft rocks than the ISRM-suggested method.

Dynamic compressive properties of Kalgoorlie basalt rock

In this study, the basalt rock extracted from the Kalgoorlie region of Western Australia is intensively studied on its compressive properties under both static and dynamic loads covering strain rate between 2.22 × 10-6/s to 408/s. The ultimate compressive strength and corresponding failure strain are quantified. The test results show that Kalgoorlie basalt rock exhibits high sensitivity to strain rate effect on its compressive strength especially above 100/s and dynamic increment factor up to 2.3 at strain rate 403/s. The failure strain also shows dependency to high strain rate. Discussion is made on fragment analysis which found the natural heterogeneous and anisotropic of WA basalt rocks cause variations on its compressive strength and dependent on the failure angle of the joints (layer formation). The dynamic increase mechanism on material compressive properties is observed to be correlated to the failure crack path formation, which can be explained through the fracture process captured from high-speed camera images analysis. Comparisons are also made on rock strengths with others’ test data. A novel method based on numerical modelling is introduced which removes the influence of lateral inertia effect and specimen end friction effect out of the laboratory testing results. The true dynamic increase factor (DIF) for Kalgoorlie basalt rock at different strain rates are derived for more accurate analysis and design.

Experimental Study on Energy Evolution and Failure Characteristics of Rock–Coal–Rock Combination with Different Height Ratios

Compared with the surrounding rock of single rock roadway, the uneven deformation of surrounding rock of thin coal seam roadway is more prominent. This uneven deformation characteristic of thin coal seam surrounding rock between the different surrounding rocks has greatly hindered the mining of thin seam coal mines. Based on the uniaxial loading tests and uniaxial cyclic loading tests of the coal–rock combination, the deformation characteristics and loading failure of coal–rock combination with different height ratios of coal to rock is studied. The results show that the uniaxial compression strength of coal–rock combinations increases with coal height. By comparing and analyzing the energy evolution of the composite with different height ratio, the energy dissipation of the coal–rock combination decreases suddenly between RCR-0.5 and RCR-1 specimens. The coal body is constrained by the sandstone at both ends of the composite specimen, which improved the strength of the coal body. The effect of this constraint decreases with the distance from the coal–rock interface. The failure mode of the composite specimens is dominated by the coal body, which is from splitting failure to shear failure finally becomes middle coal extrusion.

Analysis of the bond behavior difference in steel and steel fiber reinforced concrete (SSFRC) composite member with circular section

In order to solve the difficulties in the construction of Concrete Encased Steel (CES) structure, Steel and Steel Fiber Reinforced Concrete (SSFRC) was proposed by replacing the traditional rebar cages with discrete steel fibers. It is a basic principle for the bond behavior between steel and steel fibers reinforced concrete (SFRC) to ensure the co-working of two materials. The standard push-out test of 16 circular specimens which were designed with different steel fiber ratio (ρsf), different embedded length of reinforcing steel (Le) and different concrete thickness (Css) have been carried out. That is for the study of bond behavior and interface damage between steel and SFRC without rebar cages. The load–displacement curves, coefficient of displacement difference, interface energy dissipation and other important performance indices are obtained. The results show that the displacement of the free end doesn’t keep level with the loading end, and the relative slip occurs at the free end before the loading end. The displacement difference between two ends reaches the maximum under the ultimate load. The longer Le, the more significant the displacement difference and interface energy dissipation difference, and with bigger Css, the opposite is true. The damage difference between two ends of specimens is all found after a certain relative slip. The damage variable of the free end is always ahead of the loading end, and with the increase of ρsf, Le or Css, the development of relative slip and interface damage are slower. Increasing the Css is beneficial for plastic redistribution of bond stress along with the interface and reduce the damage difference between two ends. When the Css or ρsf grow, the influence of other design parameters on the maximum damage difference becomes more and more obvious.

Discrete lattice fracture modelling of hydrated cement paste under uniaxial compression at micro-scale

A combination of laboratory experiments and numerical simulations at multiple length scales can provide in-depth understanding of fracture behaviour of hydrated cement paste (HCP). To that end, the current work presents a numerical study on compressive failure of hydrated cement paste (HCP) at the micro-scale. Virtual specimens consisting of various phases were obtained using a combination of X-ray computed tomography and image segmentation techniques. The discrete lattice fracture model was used for the deformation and fracture analysis of the specimens subjected to uniaxial compression. The input local mechanical properties of each individual phase were taken from the literature in which a micro-scale compression test was conducted for the calibration of the same type model. The influence of slenderness ratios (1 and 2), water-to-cement ratios (0.3, 0.4 and 0.5 respectively) and lateral confinement of the specimen ends (free and restricted) on the failure behaviour were investigated. It has been shown by the current study that the stress–strain response cannot be completely separated from the used boundary conditions. The proposed model provides an effective tool to understand the compressive fracture behaviour of cement paste at the micro-scale.

Influence of joint location and connectivity on the shear properties of artificial rock samples with non-persistent planar joints

In this paper, direct shear tests of cement mortar samples with non-persistent planar joints are reported, to study the effects of joint connectivity ratio k (ratio of the length of the planar joint to the length of the specimen) and locations of a planar joint on the shear properties of artificial jointed rock samples. The test results indicate that (a) the shear stress-shear displacement curve of samples with non-persistent planar joint under direct shear stress consists of five stages. (b) For samples with a non-persistent planar joint, when the joint connectivity ratio k remains unchanged, the shear strength of the specimen increases as the distance s between the left end of the planar joint and the left edge of the specimen increases. When the distance s remains constant, the shear strength of the specimens increases with an increase in the joint connectivity ratio k. When both the joint connectivity ratio k and the distance s remain unchanged, the shear strength increases as higher normal stress is applied. (c) For samples with two non-persistent planar joints and constant joint connectivity ratio k, the shear strength increases as the two planar joints, respectively, are at the two ends of specimen, compared to the scenario where the two planar joints are at the middle of the specimen. The results also demonstrate that the proposed fitting model is suitable for characterizing the shear stress-shear displacement of artificial jointed rock specimens where a non-persistent planar joint is present.

Research on strain distribution and damage behavior of thermal barrier coatings based on digital image correlation

AbstractDue to the complicated structure and serving environments, thermal barrier coatings (TBCs) usually encounter failure in the form of surface coating cracking and interface spalling without warning. At present, although many experimental techniques and equipment were developed to predict their service life, the transfer process of stress between different layers and the strain characteristics of ceramic surface are not clearly explained. In this paper, the nondestructive digital image correlation method was used to observe the character of surface strains of supersonic plasma‐sprayed TBCs systems in tensile failure processes. Also, mathematical model was established basing on the principle of minimum function to calculate interface stress and coating strain expressions. The results show the characteristics of strain change in the whole tensile stage can be divided into four stages. At first, strain concentration occurs in the range of 9%‐27% of the effective distance between one end of the tensile specimen, second, a certain number of strain fringes are formed and distributed at a certain distance, and then the first crack appears in the initial strain concentration area; as the load continues, more and more cracks on the coating surface reach saturation and finally fail. In the microlinear elasticity stage, the shear strain in the coating and the interface shear stress are in a linear relationship. As the thickness of the single‐layer coating increasing, the strain value of the surface strain of the coating decreases, the surface strain value of the single‐layer coating is about six times larger than that of the double‐layer coating.

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.

Dynamic tensile behavior of rocks under static pre-tension using the flattened Brazilian disc method

Rocks in underground engineering projects, are likely to be subjected to static pre-stress and dynamic loading simultaneously. To measure the tensile strength of brittle rocks under coupled static-dynamic loads, a coupled static-dynamic flattened Brazilian disc (FBD) testing method is proposed in this study via a modified split Hopkinson pressure bar (SHPB) system. Our method has unique advantages on coupled static-dynamic tests using SHPB, because under different static pre-loads, the contact area between the loading platens and the specimen remain nearly constant, contributing to maintaining a consistent contact condition. Using the method, we experimentally and numerically investigate the tensile response of sandstone subjected to different static pre-tensions and different dynamic loading rates. By careful pulse shaping, the dynamic force equilibrium on both loading ends of FBD specimens can be satisfied. Detailed progressive fracture processes of tested specimens are captured via a high-speed camera, and the central crack initiation is observed in all our coupled static-dynamic tests. The dynamic tensile strength of sandstone decreases with the increase of the pre-tension, while the total tensile strength features an increase, and both the dynamic tensile strength and total tensile strength show the obvious rate dependence. The numerical simulation reveals that under a higher pre-tension ratio, more microcracks are observed at the static pre-tension stage, suggesting that more damage is induced in the rock. Our method is feasible to indirectly measure the tensile strength of rocks under coupled static-dynamic loads.

High Temperature Compression Tests of A Commercial Isotropic Ultrafine Grain Graphite

Graphite is often used to design components working at high temperature in a variety of industrial and research environments. It is therefore important to know the mechanical resistance of this material at high temperature. This work reports the compressive strength up to 2000°C of an isotropic ultrafine grain graphite, the POCO EDM-3, which has not been analysed in the literature yet. This graphite is used to design components able to withstand extreme environmental conditions, due to the properties resulting from the uniform and isotropic microstructure of the material. A vacuum compression test equipment was developed, able to work above 2000°C. Both cylindrical and hourglass-shaped specimens were tested and the influence of density was also evaluated. The influence of the materials in contact with the specimen ends was also analysed, but a negligible dependence was observed. The tests demonstrated that the compressive strength increases as the density and the temperature increase: at 2000°C a 22% average increase of the compressive strength over its room-temperature value was noted.

Study of ultrasonic vibration-assisted forming in copper cylinder compression

To investigate the effects of ultrasonic vibration on copper cylinder compression, the ultrasonic vibration-assisted forming system was developed and the ultrasonic vibration-assisted compression experiments were carried out on copper cylinders. Experiment results show that the ultrasonic vibration could cause the geometry effect and the softening effect. The end of the copper specimen shows different shapes with different ultrasonic powers. When the ultrasonic power reaches 1.8 kW, the specimen takes on an inverted drum shape. By measuring the forming force during the ultrasonic vibration -assisted compression, it is confirmed that the copper specimens are softened at different modes under different ultrasonic powers. To test the forming process, an ultrasonic vibration was superimposed on the specimen placed in the mold by a series of preloading forces. These results in combination with the stiffness characteristics of the forming system reveal that ultrasonic vibration can reduce the yield stress of copper.

DIRECT MEASUREMENT OF REACTION FORCES DURING FAST DYNAMIC LOADING

The presented paper is focused on embedding of the serially manufactured piezo-electric impact loadcell into Open Hopkinson Pressure Bar (OHPB) and it’s modifications for a direct force measurement during dynamic loading. Conventionally, during the SHPB test dynamic force equilibrium is investigated by a comparison of the transmitted signal wave and the difference between the incident, reflected and transmitted signals measured by strain gauges [1]. However, in the experiments with specimens with low mechanical impedance, a major portion of the incident wave is reflected back on the interface between the bar and the specimen. Comparison between two-large amplitude incident and reflected pulse and a small-amplitude transmitted pulse can be influenced by large error and resulting force equilibrium can be inaccurate. Therefore, a piezo-electric quartz impact force transducer was used to directly measure the axial forces in the vicinity of the specimen end surfaces.

Expansion of Prior Existing TP53 Mutated Clones in Polycythemia Vera Patients Treated with Idasanutlin

Expansion of Prior Existing TP53 Mutated Clones in Polycythemia Vera Patients Treated with Idasanutlin

Finite element optimization of sample geometry for measuring the torsional shear strength of glass/metal joints

Assessment of mechanical properties of glass/metal joints is a challenging process, especially when the application relevant conditions of the joints have to be considered in the test design. In this study, a finite element method (FEM) is implemented to analyze a torsional shear strength test designed for glass-ceramic/steel joints aiming towards solid oxide fuel/electrolysis cells application. Deviations from axial symmetry of the square flanges (ends) of respective hourglass-shaped specimens and also supporting and loading sockets of the test set-up are included in the model to simulate conditions close to reality. Undesirable tensile stress and also shear stress concentration appear at the outer edge of glass-ceramic layers, which are less for the hollow-full specimen. The simulation results show that for a specimen with either 9 mm thick square- or 6 mm thick triangular-flanges, locally enhanced tensile stresses almost disappear, resulting in a symmetric shear stress distribution. The difference between the analytically derived nominal shear strength and the real critical shear stress derived via simulation reduces with decreasing the fracture torque.

Experimental investigation on axial compressive behavior of ultra-high performance concrete (UHPC) filled glass FRP tubes

To investigate the axial compressive behavior of ultra-high-performance concrete (UHPC)-filled fiber-reinforced polymer (FRP) tubes, a total of 54 specimens, including 42 UHPC-filled glass FRP (GFRP) tubes and 12 unconfined UHPC specimens, were prepared and tested under axial compression. The effects of curing regime, steel fiber in the UHPC core, fiber orientation of the outer FRP tube, and specimen end condition during loading were examined. The test results indicate that UHPC-filled FRP tubes can exhibit highly ductile behavior and a significant enhancement in compressive strength, compared to the unconfined specimens. However, the axial compressive behavior of UHPC-filled FRP tubes is influenced by numerous factors. Hot-water curing can improve the performance of specimens unless the contribution from the enhancement of the UHPC core exceeds that from the damage of the outer FRP tube. Specimens without steel fibers experience a sudden strength loss in the transition region of the axial stress–strain relationship, and exhibit lower ultimate strength and strain than the steel-fiber-reinforced specimens. The test results indicate that aligning fibers in the hoop direction is the most effective way of improving the compressive performance of the specimens. Regarding specimens with thicker FRP tubes, loading the FRP tube can lead to a clear decrease in specimen ultimate strain; however, the influence of specimen end condition can be ignored for specimens with thinner FRP tubes.

Abstract CT182: Neoadjuvant immuno-radiotherapy (NIRT) in head and neck cancer: Phase I/Ib study of combined PD-1/SBRT prior to surgical resection

Abstract Background: Standard treatment of locally advanced HPV-associated oropharyngeal HNSCC includes definitive chemoRT or surgery followed by risk-adapted adjuvant RT +/- chemo. These approaches provide high rates of long term survival, but are associated with significant subacute as well as long term morbidity. Therefore, increasing efforts have been directed at exploring alternative approaches. Combined SBRT and PD-1 blockade may have particularly favorable properties for anti-tumor immune response in HNSCC (Gough 2009). We present phase I safety & efficacy data from the NIRT trial of neoadjuvant nivolumab/SBRT in oropharyngeal p16+ HNSCC (NCT03247712). Methods: Patients with p16+ oropharyngeal or unknown primary HNSCC, with clinical indications for adjuvant RT, or upfront TORS ineligible due to tumor size, could enroll. Patients received Nivo 240mg IV q2wks x3 prior to surgery, with SBRT to GTV+3mm delivered between Nivo doses 1 & 2, in two dose finding cohorts (n=5 each): 8Gy x5 daily (M-F) and de-escalated 8Gy x3 (M,W,F). Surgery was performed 5 weeks post-SBRT followed by adjuvant Nivo 480mg IV q4wks x3, starting 4 weeks post-op. The primary endpoint was < 33% unplanned surgical delay; the secondary endpoint was pathologic response by irPRC (Cottrell 2018). Results: There were no unplanned surgical delays. All patients had radiologic evidence of decreased tumor size prior to surgery, but none showed a CR by RECIST. Remarkably, the pathologic CR rate was 100% in the 8Gy x 5 cohort (5/5) and 80% In the 8 Gy x 3 cohort (4/5), with the remaining patient achieving MPR (major pathologic response; <10% residual viable tumor). G3 toxicity was observed after surgery in both cohorts but was higher in the 8 Gy x 5 cohort. No G4 or higher toxicity was observed. Interestingly, G2 adrenal insufficiency was observed in 50% (5/10), a higher rate than previously reported with PD-1 blockade for recurrent/metastatic HNSCC. Notably, patients did not experience xerostomia or ageusia rates associated with standard adjuvant radiation in HNSCC. Tissue responses were characterized by robust inflammatory infiltrates into the regression bed and cholesterol clefts, as previously described. Circulating immune cells, baseline tissue, end of RT biopsy and surgical specimen were analyzed using flow cytometry and RNAseq to characterize of immunologic changes over time. There have been no local or distant failures, but median follow up remains < 1 year. Conclusions: Neoadjuvant combined PD-1/SBRT to GTV+3mm dosed at either 8Gy x5 (M-F) or 8Gy x3 (M,W,F) did not delay HNSCC surgery in this Phase I trial (n=10; five per dose). Potent anti-tumor response was observed in all cases (CR=9 + MPR=1). A high response rate and lower toxicity profile favors the 8Gy x3 cohort for development. This study represents a major paradigm shift in the approach to treatment of locally advanced p16+ oropharyngeal cancers. Citation Format: Rom Leidner, R. Bryan Bell, Kristina Young, Brendan Curti, Marcus Couey, Ashish Patel, Amber Watters, Hong Xiao, Carlo Bifulco, Brian Piening, George Morris, Lessli Rushforth, Dawn Brucker, Shorin Nemeth, Michael Gough, Marka Crittenden. Neoadjuvant immuno-radiotherapy (NIRT) in head and neck cancer: Phase I/Ib study of combined PD-1/SBRT prior to surgical resection [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr CT182.

Measurement of thermal conductivity for frozen soil at temperatures close to 0 °C

A Fourier’s law–based approach that can be used for measuring multiple thermal conductivities in one specimen simultaneously at temperatures close to 0 °C is described. The temperature gradient between neighboring points was observed, and the heat flux was the product of thermal conductivity from transient–state method and temperature gradient near specimen end with a temperature much lower than 0 °C. Distinguished from the thermal conductivity of frozen soil samples with low temperatures, the measured thermal conductivity of frozen soil samples at temperatures near 0 °C increased as temperature decreased, and the average increasing–rate of thermal conductivity was greater than 0.1W/(m∙K)/°C. The developed approach validated by the independent estimations from the empirical model in literatures, and is expected to be an effective technique for measuring thermal conductivity for frozen soils with a wide range of temperatures.