Search

The Small Punch Test (SPT) method is especially useful for quantifying the mechanical properties of metallic materials in cases where the material available for testing is limited or for in service monitoring. However, the applicability of this method to metal matrix composites has not yet been fully established. In the present study, Al-TiB2 composite billets with TiB2 particle volume fractions of 5%,10% and 15% were manufactured using Spark Plasma Sintering (SPS). Thin specimens with 0.5 mm thickness were cut from the billets, and SPT experiments were conducted until failure. Well-accepted analytical techniques were utilized to determine the Al-TiB2 composite effective yield stress for all TiB2 particle volume fractions. It was shown, that standard analytical methods for characterizing the effective yield stress were adequate only for TiB2 volume fractions of up to 5%. The experimental mechanical response up to and including failure was reproduced for all Al-TiB2 compositions by finite element analysis incorporating a continuum damage mechanics approach. The computational analysis revealed that for high TiB2 volume content, the region of the SPT loading curve which is commonly associated with specimen yielding, may represent a mixture of yielded and damaged areas. Since the damage distribution in the specimen influences the specimen flexural modulus, standard analytical relations cannot be used to determine the composite yield stress and computational methods must be used. This finding may explain the inconsistent results reported in the literature with regard to the accuracy of the SPT method in determining the effective yield stress for metal matrix composites. [ABSTRACT FROM AUTHOR]

The Bauschinger effect (BE) was originally defined as the phenomenon whereby plastic deformation causes a loss of yield strength restraining in the opposite direction. The Bauschinger effect factor (BEF), defined as the ratio of the yield stress on reverse loading to the initial yield stress, is a measure of the magnitude of the BE. The aim of the present work is to quantitatively evaluate the influence of plastic deformation on other material properties such as Young's modulus and Poisson's ratio for gun barrel steel, thus extending the definition of the Bauschinger effect. In order to investigate the change in this material's properties resulting from plastic deformation, several uniaxial tension and compression tests were performed. The yield stress and Young's modulus were found to be strongly affected by plastic strain, while Poisson's ratio was not affected at all. An additional result of these tests is an exact zero offset yield point definition enabling a simple evaluation of the BEF. A simple, triphase test sufficient to characterize the entire elastoplastic behavior is suggested. The obtained experimental information is readily useful for autofrettage residual stress field calculations. [DOI: 10.1115/1.2172962]

Terfenol-D, Tb(sub1-x)DYxFe(sub2) has large magnetostrictive displacements. Standard transducer designs using Terfenol-D as the actuator, incorporate a rod cast under specific cooling conditions. However the frequency range of the generated acoustic signal limits this type of magnetostrictive transducer. The alloy should be manufactured in thin strips with appropriate crystallographic orientation. A method of manufacturing thin strips of Terfenol-D is reported, based on the melt-spinning rapid solidification technique.

The effects of the secondary processes of Hot Isostatic Pressing (HIP) at 920 °C and Heat Treatment (HT) at 1000 °C of Electron Beam-Melted (EBM) Ti-6Al-4V alloy on the microstructure and hydrogen embrittlement (HE) after electrochemical hydrogen charging (EC) were investigated. Comprehensive characterization, including microstructural analysis, X-ray diffraction (XRD), thermal desorption analysis, and mechanical testing, was conducted. After HIP, the β-phase morphology changed from discontinuous Widmanstätten to a more continuous structure, 10 times and ~1.5 times larger in length and width, respectively. Following HT, the β-phase morphology changed to a continuous "web-like" structure, ~4.5 times larger in width. Despite similar mechanical behavior in their non-hydrogenated state, the post-treated alloys exhibit increased susceptibility to HE due to enhanced hydrogen penetration into the bulk. It is shown that hydrogen content in the samples' bulk is inversely dependent on surface hydride content. It is therefore concluded that the formed hydride surface layer is crucial for inhibiting further hydrogen penetration and adsorption into the bulk and thus for reducing HE susceptibility. The lack of a hydride surface layer in the samples subject to HIP and HT highlights the importance of choosing secondary treatment process parameters that will not increase the continuous β-phase morphology of EBM Ti-6Al-4V alloys in applications that involve electrochemical hydrogen environments.

Thermoelectric generators (TEGs) are devices capable of transforming heat energy into electricity and vice versa. Although TEGs are known and have been in use for around five decades, they are implemented in only a limited range of applications, mainly extraterrestrial applications. This is due to their low technical readiness level (TRL) for widespread use, which is only at levels of 3-5 approaching laboratory prototypes. One of the most setbacks in reaching higher TRL is the lack of understanding of the mechanical and thermo-mechanical properties of TE materials. Out of ~105,000 entries about TE materials only ~100 entries deal with mechanical properties, while only 3 deal with thermo-mechanical properties. GeTe-based alloys with varying other elements, forming efficient p -type thermoelectric materials in the 200 ÷ 500 °C temperature range, have been intensively researched since the 1960s and have been successfully applied in practical TEGs. Yet, their temperature-dependent mechanical properties were never reported, preventing the fulfillment of their potential in a wide variety of practical applications. The combined effects of temperature and mechanical compression of GeTe were explored in the current research by implementing novel quantitative crystallographic methods to statistically describe dislocation activity and modification of the micro-texture as inflecting by the testing conditions. It is suggested, through utilizing these methods, that the combined effect of compression and temperature leads to the dissolving of twin boundaries, which increases dislocation mobility and results in a brittle-to-ductile transition at ~0.45 of the homologous temperature.

Objective: Cervical ripening by mechanical methods enhances labor induction success. We compared Cervical Ripening Double Balloon catheter (CRDB) to Foley catheter., Study Design: This prospective blind study randomized 85 nulliparas and 95 multiparas to labor induction by either Foley catheter or CRDB. Primary outcomes were Bishop score increment, time from catheter withdrawal to delivery, and cesarean section rate., Results: In multiparas, mean Bishop score increment between pre- and post-catheter was significantly higher in the CRDB catheter than in the Foley group (4.4 ± 1.9 and 3.4 ± 2.0, respectively, p  = .02). Mean interval from catheter withdrawal to delivery was shorter in the CRDB catheter (14.6 ± 12.3 and 8.6 ± 5.4) than in the Foley catheter group (22.6 ± 27.2 and 13.9 ± 17.7), in both nulliparas and multiparas ( p  = .05 and p  = .03, respectively). In nulliparas, no statistically significant differences were found in mean Bishop score increment between the two catheters, but cesarean section rate was higher in the Foley group than the CRDB group (46.5% and 20%, respectively, p  = .02)., Conclusion: Bishop score increment by CRDB catheter is more effective than induction by Foley catheter in multiparas. CRDB catheter is associated with decreased time to delivery in both nulliparas and multiparas and a lower cesarean section rate in nulliparas. ClinicalTrials.gov Identifier: NCT00501033.

Cerebrotendinous xanthomatosis (CTX) is a progressive metabolic leukodystrophy. Early identification and treatment from birth onward effectively provides a functional cure, but diagnosis is often delayed. We conducted a pilot study using a two-tier test for CTX to screen archived newborn dried bloodspots (DBSs) or samples collected prospectively from a high-risk Israeli newborn population. All DBS samples were analyzed with flow injection analysis (FIA)-MS/MS, and 5% of samples were analyzed with LC-MS/MS. Consecutively collected samples were analyzed to identify CTX-causing founder genetic variants common among Druze and Moroccan Jewish populations. First-tier analysis with FIA-MS/MS provided 100% sensitivity to detect CTX-positive newborn DBSs, with a low false-positive rate (0.1-0.5%). LC-MS/MS, as a second-tier test, provided 100% sensitivity to detect CTX-positive newborn DBSs with a false-positive rate of 0% (100% specificity). In addition, 5β-cholestane-3α,7α,12α,25-tetrol-3- O -β-D-glucuronide was identified as the predominant bile-alcohol disease marker present in CTX-positive newborn DBSs. In newborns identifying as Druze, a 1:30 carriership frequency was determined for the c.355delC CYP27A1 gene variant, providing an estimated disease prevalence of 1:3,600 in this population. These data support the feasibility of two-tier DBS screening for CTX in newborns and set the stage for large-scale prospective pilot studies., (Copyright © 2018 DeBarber et al.)

PH13-8Mo is a precipitation hardened martensitic stainless steel, known for its high strength but also for its high sensitivity to hydrogen embrittlement. Small punch test, SPT (also referred to as the ball punch test, BPT), is a relatively simple and new technique to assess the mechanical properties of samples under biaxial loading conditions. The current study utilizes the unique loading conditions of SPT to investigate the mechanical behavior and fracture prior to and after the hydrogen charging of PH13-8Mo steel. The mechanical characteristics were investigated at different metallurgical conditions: solution and quenched (SQ); fully-aged (550 °C for 4 h) and over-aged (600 °C for 4 h). Samples were cathodically hydrogen charged in a 1 M H₂SO₄ solution containing NaAsO₂ (0.125 mg/L) at 50 mA/cm² for different durations of 0.5 h, 2 h, and 19 h, and compared to the as-heat-treated condition. A fractographic examination was performed following the SPT measurements by scanning electron microscopy (SEM). Transmission electron microscopy (TEM) and x-ray diffraction (XRD) analyses were used as complementary characterization tools. It is shown that upon hydrogen charging, the SPT fracture mode changes from ductile to completely brittle with a transition of mixed mode cracking also affecting the SPT load-displacement curve.

Prediction of the mechanical behavior of thin foils (~25 µm) requires special characterization techniques. The current work is focused on the mechanical and microstructural characterization of 25 µm HAVAR alloy foils following annealing, cold rolling, and subsequent heat treatments, using small punch testing (SPT), X-ray diffraction (XRD), and transmission-scanning electron microscopy (TEM). The SPT technique revealed that the annealed specimens exhibited the largest maximal load to failure and deformation (more than two-fold), compared to the cold rolled and heat treated conditions. The microscopy observations revealed high dislocation density following cold rolling and subsequent heat treatments. Following annealing, a cubic crystallographic structure (FCC) with equiaxed grains and a limited dislocation population was observed. Following cold rolling and subsequent thermal treatment, a preferred orientation texture (i.e., 'deformation texture') was observed with a very high dislocation density. The correlation between the mechanical behavior and the microstructural observations is discussed in detail., Competing Interests: The authors declare no conflict of interest.