Specimen Failures Research Articles

Comprehensive evaluation of CFRP laminates using NDT methods for aircraft applications

The evaluation of carbon fiber reinforced polymers (CFRP) laminates during and after the Mode I test was successfully conducted, integrating non-destructive testing of acoustic emission (AE) and ultrasound scanning. Two different specimens [+45°/-45°/0°]2S and [0°/+45°/-45°]2S were used to detect the effects of stacking sequences of the laminates. Results indicated that applying AE sensors to the specimens slightly affect to the laminate performance. Thus, the laminates are validated and showed that for [+45°/-45°/0°]2S laminates, the system can withstand load and increase the displacement at break more than twice of [0°/+45°/-45°]2S laminates. Moreover, the ultrasound scanning showed that the crack trace is visible. [+45°/-45°/0°]2S laminates have smaller crack around 24 mm compared to [0°/+45°/-45°]2S laminates with 30 mm. Image analysis revealed that after specimen are forced to open, the [+45°/-45°/0°]2S laminates can prevent long crack compared to [0°/+45°/-45°]2S laminates. The double cantilever beam (DCB) test, employing various stacking sequences, demonstrated excellent examination results using non-destructive testing. Theoretical calculations regarding residual thermal expansion due to different coefficients of thermal expansion also revealed a slight impact of varying manufacturing temperatures on the laminates. These findings offer valuable insights for detecting, predicting, and preventing specimen failures in aircraft and aerospace structures without resorting to destructive examinations, facilitating appropriate preventive maintenance.

Mechanical properties and failure mechanism of rock-like specimens with arc-shaped flaws under freeze–thaw cycles

To investigate the failure characteristics of jointed rock masses in cold regions after freeze–thaw (F-T) cycles, uniaxial compressive tests are conducted on rock-like specimens (a type of cement mortar) with prefabricated arc-shape flaws subjected to 0, 25, 50 and 100F-T cycles to determine their mechanical properties. Test results reveal that F-T cycles greatly affect the uniaxial compressive strengths (UCS) of the specimens, and the relationship between the peak strength and the number of freeze–thaw cycles is exponentially fitted. Notably, the initial 50 cycles have a more pronounced effect on UCS reduction compared to the subsequent 50 cycles, indicating that early F-T cycles are more detrimental to UCS. To further investigate the failure mechanism of the specimens, two-dimensional particle flow code (PFC2D) is utilized to simulate the F-T cycle process of the specimens. The mechanical properties and failure mechanism of specimens can be obtained after F-T cycles under uniaxial compression through numerical simulations. The findings indicate that F-T cycles can obviously deteriorate the ductility of the specimens, and to some extent, they also affect crack propagation during specimen failures. Through crack classification statistics and stress contour analysis of the simulated specimens, it reveals that different prefabricated flaw morphologies lead to distinct stress distributions, subsequently affecting crack propagation and specimen failure. It is also worth mentioning that the large curvature and inclination angle of the flaws may generate additional tensile and shear stress zones at the top of the flaw vault, which in turn may contribute to the development of crack propagation. The relevant experimental and numerical results are useful for investigating mechanical properties and failure mechanisms of rock masses in cold regions subjected to F-T cycles.

Facilitating the Systematic Nanoscale Study of Battery Materials by Atom Probe Tomography through in‐situ Metal Coating

AbstractThrough its capability for 3D mapping of Li at the nanoscale, atom probe tomography (APT) is poised to play a key role in understanding the microstructural degradation of lithium‐ion batteries (LIB) during successive charge‐ and discharge cycles. However, APT application to materials for LIB is plagued by the field induced delithiation (deintercalation) of Li‐ions during the analysis itself that prevents the precise assessment of the Li distribution. Here, we showcase how a thin Cr‐coating, in‐situ formed on APT specimens of NMC811 in the focused‐ion beam (FIB), preserves the sample's integrity and circumvent this deleterious delithiation. Cr‐coated specimens demonstrated remarkable improvements in data quality and virtually eliminated premature specimen failures, allowing for more precise measurements via. improved statistics. Through improved data analysis, we reveal substantial cation fluctuations in commercial grade NMC811, including complete grains of LiMnO. The current methodology stands out for its simplicity and cost‐effectiveness and is a viable approach to prepare battery cathodes and anodes for systematic APT studies.

Research on Compressive Tests of Iron Tailing and Cement-Modified Earth Materials from Northwest China

The strength of earth-modified materials is an important mechanical indicator of raw soil building materials. Iron tailings are a rich mineral waste resource with basic properties similar to river sand and can be used as a modified material for raw soil construction. To increase the utilization rate of iron tailings and improve the mechanical properties of earth materials, modification of earth materials were analyzed using iron tailings and cement. Through a single lattice theory design method, 10 different blending ratios of modified earth specimens were designed, with each group comprising six 100 mm cubic specimens. Earth specimens were used as the control group and compression tests carried out under standard curing conditions, with analysis of the failure mode, compressive strength, deformation, and load–displacement curve for each specimen. Also, the reasons for specimen failures were examined, including the influence of strength, dispersion, and implications of load–displacement curves. The optimal mix ratio of modified materials was determined using frequency domain analysis method. The results showed that the load–displacement curves of materials with different material ratios were basically similar and the slope and discreteness of the curves quite different. Increased tailings and cement content improved the compressive strength of earth materials and increased the discreteness of the material. Through frequency analysis, it was obtained that when the content of tailings was 12.1%–19.5%, cement content 13.9%–19.1%, and earth 65.5%–69.9%, there was a 95% of the guaranteed rate of compressive strength of iron tailings and cement-modified earth materials between 6 and 9 MPa. Iron tailings can, thus, be used as the preferred material for modifying earth materials; single lattice theory can be used as the design method for mixing experiments, and frequency domain analysis can be an effective calculation method for optimizing mixing design. Adding cement and iron tailings to modify the raw soil formula can provide reference for the selection of basic materials for raw soil construction.

Effect of build interruption during laser powder bed fusion process on structural integrity of Ti-6Al-4V

The growing concern for global sustainability highlights the need to address waste generation in metal additive manufacturing (AM) processes. Even with proper planning, unexpected incidents such as software glitches and power outages may interrupt AM processes by pausing the build sequence, leading to a waste of resources (i.e. time, money, and materials). The layer-wise nature of AM processes allows for interrupted builds to be resumed from the stopping point. Nevertheless, interrupting the build process (i.e. pausing and resuming) can compromise the structural integrity of the fabricated parts, potentially leading to localized failure near the interruption location. The objective of this study is to investigate the effect of build interruption during the laser beam powder bed fusion process on the structural integrity of Ti-6Al-4V specimens. Tensile and fatigue tests were performed to assess any possible contribution of build interruption to the specimen failures under monotonic and cyclic loading, and the results were compared with their control counterparts, fabricated without interruption. Tensile and fatigue failures as well as the propagation of a secondary crack were observed at the interruption location. Our experimental observations indicate that when large process-induced defects are present, build interruption plays a peripheral role in the fatigue life and failure mechanism of specimens, with defects being the overriding factor. None of the heat-treated specimens exhibited any tensile or fatigue failures at the interruption location, suggesting that an appropriate heat treatment can be effective in reducing the risk of localized failure near the interrupted location.

Comparison of the clinical and pathological characteristics of ultrasound-guided biopsy for breast masses and non-mass lesions between 16-gauge spring-loaded core needle biopsy and 12-gauge spring-loaded vacuum-assisted biopsy.

To retrospectively compare the clinical and pathological characteristics of breast masses and non-mass lesions that underwent ultrasound (US)-guided 16-gauge spring-loaded core needle biopsy (CNB) or 12-gauge spring-loaded vacuum-assisted biopsy (VAB). We retrospectively compared the results from US-guided diagnostic breast biopsy performed with a 16-gauge CNB (Magnum™) or a 12-gauge VAB (Celero®). The patients' backgrounds and pathological features for each device were examined. In 453 patients with 500 lesions, 373 lesions underwent CNB and 127 underwent VAB. The positive biopsy rate (positive predictive value 3) was significantly higher for VAB (92/127; 72.4%) than for CNB (231/373; 61.9%) (P = 0.032). Non-mass lesions were biopsied more frequently with VAB (57/127; 47.4%) than with CNB (27/378; 7.14%) (P = 0.000). The upgrade rate from high-risk to malignant lesions was significantly higher for CNB (5/19; 26.3%) than for VAB (1/8; 12.5%) (P = 0.043). There were five (1.34%) specimen failures with CNB and one (0.78%) with VAB, 18 (4.82%) re-biopsies with CNB and three (2.36%) with VAB, and 11/21 (52.4%) upgrades from ductal carcinoma in situ (DCIS) to invasive ductal carcinoma (IDC) with CNB and 11/30 (36.7%) with VAB. Although these rates tended to be higher with CNB than with VAB, the difference was not significant. Although VAB had a significantly higher rate of non-mass lesion biopsies, the upgrade rate from high-risk to malignant lesions was significantly lower for VAB than for CNB. US-guided 12-gauge spring-loaded VAB may be more appropriate for biopsy of non-mass lesions.

Experimental Investigation of the Mechanical Behavior of Layer-Crack Specimens under Cyclic Uniaxial Compression

It is generally acknowledged that the failure of the layer-crack structure is closely related to rock bursts (a layer-crack structure means a coal or rock rib that is cut by fractures that are parallel or sub-parallel to the surface of the rib). Understanding the mechanical behavior of the layer-crack structure under cyclic loading is beneficial for rock burst mitigation. This study experimentally investigated the influence of the geometry of vertical fissure (i.e., width, length and number) on the mechanical properties of layer-crack rock specimens. The results show that the sensitivity of parameters with respect to the geometry of the fissure from strong to weak is the number, length and width. First, the peak stress under cyclic loading increases by approximately 7.82–17.35%, thereby exerting an obvious strengthening effect. Second, the fissure geometry slightly affects the energy evolution of the layer-crack specimen, i.e., the input energy density, elastic energy density and dissipated energy density all gradually increase with the increase of the number of cycles. However, when approaching a specimen failure, the increasing rates from quick to slow are the dissipated energy, input energy and elastic energy. Third, the damage variable of the layer-crack specimen shows a concave increasing trend with the increase of the number of cycles. When the number of cycles is equal, the damage increases with the increase of the number of fissures, but it decreases with the increase of the fissure length. Fourth, AE events occur shortly before specimen failures, but rapidly increase near the specimen failures. The accumulated AE events that lead to specimen failures decrease with the increase in the number of fissures. These results can provide some basic data for the research of rock bursts related to the failures of layer-crack structures.

Fatigue Behaviour of Bolted Connections Applied in Racking Structures. Experimental Perspective

Racking systems, applied in logistics warehouses, are often built using zinc-coated thin steel plates that are joining by bolted connections. In fully automatic systems, these structures are loaded 7/7 days and 24/24 hours raising fatigue issues due to the cyclic nature of the resulting stresses. FASTCOLD project intends to provide fatigue design rules because until nowadays there is no reference about fatigue rules of bolted connections between thin-walled cold-formed steels, under diverse preloaded bolts, including snug tight condition. This work revealed differences between S-N curves suggested by Eurocode 3 and fatigue data obtained experimentally. In addition, preloaded bolts presented better fatigue resistance than snug tight bolts; the use of multiple bolted joints also improves the fatigue resistance due to the joint effect of bolts. Failed specimens showed that if the bolts preload and applied load level are respectively high and low enough, the specimen failures occurs along the gross cross-section, near the hole vicinity, instead of the typical net cross-section failure as occurred in single and multiple connections with snug tight bolts.

Very high cycle fatigue testing of concrete using ultrasonic cycling

Abstract The ultrasonic fatigue testing method has been further developed to perform cyclic compression tests with concrete. Cylindrical specimens vibrate in resonance at a frequency of approximately 20 kHz with superimposed compressive static loads. The high testing frequency allows time-saving investigations in the very high cycle fatigue regime. Fatigue tests were carried out on “Concrete 1” (compressive strength fc = 80 MPa) and “Concrete 2” (fc = 107 MPa) under purely compressive loading conditions. Experiments at maximum compressive stresses of 0.44 fc (Concrete 1) and 0.38 fc (Concrete 2) delivered specimen failures above 109 cycles, indicating that no fatigue limit exists for concrete below one billion load cycles. Resonance frequency, power required to resonate the specimen and second order harmonics of the vibration are used to monitor fatigue damage in situ. Specimens were scanned by X-ray computed tomography prior to and after testing. Fatigue cracks were produced by ultrasonic cycling in the very high cycle fatigue regime at interfaces of grains as well as in cement. The possibilities as well as limitations of ultrasonic fatigue testing of concrete are discussed.

Abstract 4496: Genomic profiling of late stage tumors powering precision medicine in Japan

Abstract Much evidence has shown that genomic profiling of tumors provides patients with treatment options specific to their tumor's biology in the US. Within the Kyoto University Hospital Cancer Center, we offer patients access to these tests through the OncoPrimeTM for those patients of cancer with unknown primary (CUP), rare tumor types or for which standard treatment options have failed. Our institution sees over 6,000 cancer patients each year with over 1,500 receiving chemotherapy and a progressive climate makes this kind of testing favorable. We aim to demonstrate the efficacy of genomic profiling along with successful execution of international specimen logistics as FFPE samples are shipped to EA Genomics and clinical report is provided within 3 weeks. We officially launched the product publicly in March 2015 and the majority of patients have paid for testing out of pocket in lieu of insurance coverage. During this first year, we saw 30% of patients with CUPs, and 16% of both pancreas and biliary tract with the rest being other rare cancers. Patients going through the testing were generally successful (93.5%) with the specimen failures likely indicative with FFPE artifacts or severe tumor heterogeneity. Actionabilty for our population (84.8%) is consistent with previously published numbers for information provided in the clinical report. Additional information was collected after the clinical reports to determine early indicators of follow up and see that the accepted term ‘actionability’ holds different meaning during the practice of patient care. While we had 17% of patients receive the suggested indication we have yet seen positive response from patients who have returned for follow-up. Selected tissues were tested by alternative profiling vendors, and in one case alternate action with Erlotinib was recommended by one vendor; this action has shown promising response. This suggests that heterogeneous interpretation is still a largely unsolved issue with genomic profiling. This may suggested that interpretation is still a largely unsolved issue with genomic profiling. While almost all other patients tested qualified for clinical trials (84.8%) we noted 3 main barriers to entry: geography, cost of intervention and deterioration of patient condition. We show our results in line with previous studies but strive to increase adoption of results and are compiling information of pan cancer biomarker statuses and treatment success/failures to improve interpretation prior to wider adoption of this kind of testing. Citation Format: Masashi Kanai, Matthew Schu, Tomohiro Sakuma, Steven Abbott, Tadayuki Kou, Ross Gagnon, Thomas Halsey, Shigemi Matsumoto, Mayumi Kamada, Masahiko Nakatsui, Yasushi Okuno, Akinori Hiroshima, Hiroaki Mochizuki, Patrick Hurban, Manabu Muto, Victor J. Weigman. Genomic profiling of late stage tumors powering precision medicine in Japan. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 4496.

Evaluation of FRP/wood adhesively bonded epoxy joints on environmental exposures

This article describes the evaluation of the durability of joints composed of wood adherends with a bonded layer of fibre-reinforced polymer (FRP) fabric. Carbon and glass fibres in an epoxy matrix were studied. The main purpose of FRP usage with timber in the construction industry is generally to improve the stiffness/strength of reinforced members without any influence on their service-life or any environmental impact. From the perspective of the timber reinforcement process, optimal dimensional stability during moisture changes in wood should be one of the most important criteria for such joints. Therefore, FRP/wood joints were evaluated with regard to the influence of real external environmental conditions on the bondline over a period of 40 months. During exposure to these conditions, specimen failures and defects were continuously visually evaluated. The decisive factor in this evaluation was bond integrity, verified by the tensile shear strength of the FRP/wood joint. After the experimental study, it was noted that the first 20 months have a significant effect on bondline failure occurrences, which involve decreases in tensile shear strength. In the next 20 months, the FRP/wood bondlines resist other severe hygrothermal stresses without significant strength decreases. An additional observed parameter was the percentage of wood failure in the bonded area of single lap joints, which characterises the mode of failure of the bonded joint. To determine the influence of ageing on adhesive due to ultraviolet radiation and varying temperature, infrared absorption spectroscopy analysis was performed to reveal changes in the macromolecular structure of the epoxy adhesive. Findings showed that UV radiation had a significant influence on the degradation of the adhesive structure.

Influence of inclusion content on rolling contact fatigue in a gear steel: Experimental analysis and predictive modelling

Rolling contact fatigue tests were carried out on ring specimens made of quenched and tempered SAE 5135 gear steel with three different steel-production processes, through a bi-disc machine under pure rolling condition and water lubrication. Early formation of micro-pits then coalescing into macro-pits was observed on the rolling surface, while the final failure was caused by subsurface originated spalling phenomena. Microscope analysis of specimens section highlighted the complex surface and subsurface crack layout, and permitted to recognise sulphides as preferential sites for cracks initiation. The inclusion content was analysed throughout the extreme value statistics and the maximum expected inclusion in the Hertzian contact zone was introduced in a failure assessment diagram recently proposed, which resulted effective in predicting the specimen failures.

Fillet Weld Design for Rectangular HSS Connections

The 2010 AISC Specification for Structural Steel Buildings has expanded the scope in Chapter K ("Design of HSS and Box Member Connections"�) with a new Section K4, "Welds to Branches."� This paper describes the background to this development and examines the structural reliability of the weld effective length provisions contained therein. The latter is achieved by using a database of 31 welded square/rectangular hollow structural section (HSS) K-, T- and cross- (or X-) connections in which all test specimen failures were reached by fracture of the welded joints. The potential inclusion (or exclusion) of the sin θ effect, whereby fillet weld capacity is increased for loading not parallel to the axis of the weld, has also been investigated. In conclusion, some design examples are given to illustrate the weld design method, performed to the 2010 AISC Specification in both LRFD and ASD.

Fatigue resistance of the grain size transition zone in a dual microstructure superalloy disk

Mechanical property requirements vary with location in nickel-based superalloy disks. In order to maximize the associated mechanical properties, heat treatment methods have been developed for producing tailored microstructures. In this study, a specialized heat treatment method was applied to produce varying grain microstructures from the bore to the rim portions of a powder metallurgy processed nickel-based superalloy disk. The bore of the contoured disk consisted of fine grains to maximize strength and fatigue resistance at lower temperatures. The rim microstructure of the disk consisted of coarse grains for maximum resistance to creep and dwell crack growth at high temperatures up to 704 °C. However, the fatigue resistance of the grain size transition zone was unclear, and needed to be evaluated. This zone was located as a band in the disk web between the bore and rim. Specimens were extracted parallel and transverse to the transition zone, and multiple fatigue tests were performed at 427 and 704 °C. Mean fatigue lives were lower at 427 °C than 704 °C. Specimen failures often initiated at relatively large grains, which failed on crystallographic facets. Grain size distributions were characterized in the specimens, and related to the grains initiating failures as well as location within the transition zone. Fatigue life decreased with increasing maximum grain size. Correspondingly, mean fatigue resistance of the transition zone was slightly higher than that of the rim, but lower than that of the bore. The scatter in limited tests of replicates was comparable for all transition zone locations examined.

Study of dextrin-derived curing agent for waterborne epoxy adhesive

In this study, a water-soluble dextrin derivative was synthesized by reacting dextrin with trimellitic anhydride. The chemical structure of the dextrin-derived curing agent was confirmed by FT-IR and 1H NMR. The dextrin derivative contained free carboxylic acid groups and was used as curing agent for waterborne epoxy in wood bonding test. The adhesion of wood bonded by this waterborne epoxy system was studied and compared with that of wood bonded by phenol–formaldehyde resin. Results showed that the two adhesive systems displayed very similar block shear strengths and specimen failures. The two types of adhesives also showed similar extents of resin penetration into the wood substrate. This study demonstrated that starch or dextrin could be used as an economic feedstock for synthesis of curing agents for waterborne epoxies in the effort to develop formaldehyde free and volatile organic compounds (VOC)-free wood adhesives.

A Review of External Pressure Testing Techniques for Shells including a Novel Volume-Control Method

A review of conventional testing methods for applying external hydrostatic pressure to buckling-critical shells is presented. A new “volume-control” pressure testing method, aimed at preventing catastrophic specimen failures and improving control of specimen deformation near the critical load, is also introduced. The implementation of conventional and volume-control systems in an experimental program involving the destructive pressure testing of ring-stiffened cylinders is described. The volume control method was found to improve control of the specimen deformations, especially near the critical load, and catastrophic failures observed while using a conventional setup were avoided. The quasi-static tracking of postcollapse load-deformation relationships for snap-through buckling behaviour was possible while using a volumecontrol system, but precise control of dynamic shell deformations during buckling was not achieved for specimens failing with large buckling lobes. Expressions for estimating the available control over specimen deformations for pressure testing systems are presented.

High Temperature Deformation Behavior of Ti-6Al-4V Alloy with an Equiaxed Microstructure: a Neural Networks Analysis

The hot deformation behavior of Ti−6Al−4V alloy with an equiaxed microstructure was investigated by means of Artificial Neural Networks (ANN). The flow stress data for the ANN model training was obtained from compression tests performed on a thermo-mechanical simulator over a wide range of temperature (from 700°C to 1100°C) with strain rates of 0.0001 s−1 to 100 s−1 and true strains of 0.1 to 0.6. It was found that the trained neural network could reliably predict flow stress for unseen data. Workability was evaluated by means of processing maps with respect to strain, strain rate, and temperature. Processing maps were constructed at different strains by utilizing the flow stress predicted by the model at finer intervals of strain rates and temperatures. The specimen failures at various instances were predicted and confirmed by experiments. The results establish that artificial neural networks can be effectively used for generating a more reliable processing map for industrial applications. A graphical user interface was designed for ease of use of the model.

Modelling of crack coalescence in 2024-T351 Al alloy friction stir welded joints

In the present work, FSW of 2024-T351 Al alloy is characterised in terms of weld residual stress and cyclic properties. A fatigue endurance of the FSW joint was also investigated and discussed. Critical areas for natural fatigue crack initiation in FSW are pinpointed. The fatigue mechanism in FSW is identified to follow a multiple crack coalescence nature. The numbers of cracks participate in coalescence and the resulting crack growth rate is governed by the distance between the crack tips from crack initiation to coalescence. The above represents a complex condition for modelling. During fatigue bending tests, surface crack initiation and growth were monitored by means of a plastic replication technique. Detailed analysis revealed that under that the FSW specimen failures in fatigue bending tests are mainly a process of crack growth with initiation from defects and oxide inclusions, causing subsurface crack formation. Multiple crack initiation sites were observed from different microstructural regimes in the non-uniform residual stress distribution across the weld. This indicates that failure is dominated by fatigue crack propagation from defects. Therefore mechanisms that include features such as defect size and residual stress were considered when applying crack growth analyses to lifetime predictions. Based on crack growth and characterisation of FSW joints, a modified version of the Hobson–Brown is adopted. The good correlation achieved between the experimental data and the model predictions is presented in this paper. Satisfactory predictions of FSW lifetimes are derived from the model.

Shake, Rattle, and Roles: Lessons from Experimental Earthquake Engineering for Incorporating Remote Users in Large-Scale E-Science Experiments

While there has been substantial interest in using e-science and cyberinfrastructure technologies to enable synchronous remote participation in experimental research, the details of such participation are in question. On the one hand, there is a desire to give remote participants the same views and capabilities that they would have as local participants. On the other hand, there are settings where experimental specimens and apparatus are large and difficult to manipulate effectively or view from a remote vantage point. This article argues for more novel forms of remote participation by drawing on exploratory interview and observation data gathered in civil engineering laboratories. It is shown that, while experiments are in progress, the engineers studied focus primarily on detecting and preventing specimen failures, and that their unease about remote participation stems from doubts about the ability of remote participants to detect failures adequately. It is argued that this presents the opportunity to consider novel roles for remote participants that exploit the features of e-science technologies.

Multi-Stress Aging of Stator Bars With Electrical, Thermal, and Mechanical Stresses as Simultaneous Acceleration Factors

Accelerated aging tests have been carried on stator bars under simultaneous electrical, thermal and mechanical multi-stress conditions, using a simulated three-phase model stator. Over each thermal load cycle, the partial discharge activity has been found to be a strong function of temperature. Tests at twice rated electrical stress did not result in any bar specimen failures up to a total of 1500 load cycles. However, when the three phase load current was increased above its rated value, current-limited type failures were observed to occur below 1000 load cycles, thereby indicating a marked influence of thermal and mechanical stresses associated with the elevated three phase load current.