Research on low cycle fatigue life prediction considering average strain

To address the difficult problems in the study of the effect of average strain on fatigue life under low-cycle fatigue loads, the effect of average strain on the low-cycle fatigue life of materials under different strain cycle ratios was discussed based on the framework of damage mechanics and its irreversible thermodynamics. By introducing the Ramberg-Osgood cyclic constitutive equation, a new low-cycle fatigue life prediction method based on the intrinsic damage dissipation theory considering average strain was proposed, which revealed the correlation between low-cycle fatigue strain life , material properties, and average strain. Through the analysis of the low-cycle fatigue test data of five different metal materials, the model parameters of the corresponding materials were obtained. The calculation results indicate that the proposed life prediction method is in good agreement with the test, and a reasonable characterization of the low-cycle fatigue life under the influence of average strain is realized. Comparing calculations with three typical low-cycle fatigue life prediction models, the new method is within two times the error band, and the prediction effect is significantly better than the existing models, which is more suitable for low-cycle fatigue life prediction. The low-cycle fatigue life prediction of different cyclic strain ratios based on the critical region intrinsic damage dissipation power method provides a new idea for the research of low-cycle fatigue life prediction of metallic materials.

Critical Load Prediction in Notched E/Glass–Epoxy-Laminated Composites Using the Virtual Isotropic Material Concept Combined with the Average Strain Energy Density Criterion

This paper attempts to validate the application of the Virtual Isotropic Material Concept (VIMC) in combination with the average strain energy density (ASED) criterion to predict the critical load in notched laminated composites. This methodology was applied to E/glass–epoxy-laminated composites containing U-notches. For this purpose, a series of fracture test data recently published in the literature on specimens with different notch tip radii, lay-up configurations, and a number of plies were employed. It was shown that the VIMC–ASED combined approach provided satisfactory predictions of the last-ply failure (LPF) loads (i.e., critical loads).

Segmentally impaired left ventricular longitudinal strain: a new predictive diagnostic parameter for asymptomatic patients with severe aortic stenosis and preserved ejection fraction

Introduction: This study aims to investigate the correlation between severe aortic stenosis (sAS) and impairment of left ventricular global longitudinal strain (LVGLS) in particular segments, using two-dimensional speckle tracking echocardiography in patients with sAS and normal ejection fraction of left ventricle (LVEF). Methods: The study included 53 consecutive patients with asymptomatic sAS and preserved LVEF. The regional longitudinal systolic LV wall strain was evaluated at the area opposite of the aorta as the median strain value of the basal, middle, and apical segments of the lateral and posterior walls and was compared to the average strain value of the interventricular septum (IVS) at the same views. Results: LVGLS was decreased and was not statistically different between three- and four-chamber views (−12.5 ± 3.6 vs −11.4 ± 5.5%, p = 0.2). The average strain values of the lateral and posterior walls were statistically reduced compared to the average value of the IVS (lateral vs IVS: −7.8 ± 3.7 vs −10 ± 5.3%, p = 0.005, posterior vs IVS: −7.7 ± 4.2 vs −10.3 ± 3.8%, p < 0.0001). There was no significant difference between lateral and posterior walls (−7.8 ± 3.7 vs −7.7 ± 4.2%, p = 0.9). Conclusions: The strain of lateral and posterior walls of left ventricle, which lay just opposite to the aortic valve seem to be more reduced compared to other walls in patients with sAS and preserved LVEF possibly due to their anatomical position. This impairment seems to be the reason of the overall LVGLS reduction. Regional strain could be used as an extra tool for the estimation of the severity of AS as well as for prognostic information in asymptomatic patients.

The Effects of Differences in the Morphologies of the Ulnar Collateral Ligament and Common Tendon of the Flexor-Pronator Muscles on Elbow Valgus Braking Function: A Simulation Study

The anterior bundle (AB) and posterior bundle (PB) of the ulnar collateral ligament and the anterior common tendon (ACT) and posterior common tendon (PCT) of the flexor-pronator muscles have an independent form and an unclear form. The purpose of this study was to clarify the effect of differences in the morphologies of the AB, PB, ACT, and PCT on the elbow valgus braking function. This investigation examined three elbows. In the classification method, the AB, PB, ACT, and PCT with independent forms constituted Group I; the AB, ACT, and PCT with independent forms and the PB with an unclear form constituted Group II; the AB, PB, ACT, and PCT with unclear forms constituted Group III. The strains were calculated by simulation during elbow flexion at valgus at 0° and 10°. At 0° valgus, Group I and Group II showed similar AB and PCT strain patterns, but Group III was different. At 10° valgus, most ligaments and tendons were taut with increasing valgus angle. The average strain patterns of all ligaments and tendons were similar for the groups. The AB, PB, ACT, and PCT may cooperate with each other to contribute to valgus braking.

ON INVESTIGATION OF TENSILE STRENGTH OF COMMERCIAL SYNTHETIC NON-ABSORBABLE SUTURE MADE FROM OF BLUE POLYPROPYLENE MONOFILAMENT

Objective: The purpose of this research is to investigate the tensile strength of commercial synthetic non-absorbable suture made from blue polypropylene monofilament that commonly used in surgery.Methods: The commercial synthetic non-absorbable made from blue polypropylene monofilament was prepared for this purpose. The ASTM C1557-03 was used as a standard the method for analysis. For accuracy of the measurement, the diameter of the sutures was measured using optical microscope. The tensile strength, strain at failure, and modulus elasticity of the sutures were measured following instruction from the standard test method. The graph strain versus stress was provided.Results: Results show that that the average tensile strength of five valid tested samples is about 875.812 MPa. The average strain is found about 0.282. The average of modulus of elasticity is 4026.069 MPa.Conclusion: It is concluded that the sutures of commercial synthetic non-absorbable suture made from blue polypropylene monofilament having linier elastic as well as plastic properties. The average tensile strength of five valid tested samples is about 875.812 MPa. The average strain at failure is found about 0.282. The average of modulus of elasticity is 4026.069 MPa.

Plate-impact-driven ring expansion test (PIDRET) for dynamic fragmentation

A new experimental set-up mounted at the muzzle of a singlestage gas gun has been designed in order to study the fragmentation of metallic rings under dynamic radial expansion. This concept takes advantage of the quasi-incompressibility of HDPE whose radial flow under plate impact-like loading is used to apply a pressure boundary condition at the ring’s inner surface. For the experimental configurations considered in the present work, the average strain rate in the ring reaches values close to 104 s-1. The repeatability and the reliability of the experiments are verified for rings made of steel and aluminium.

Cryptic or Silent? The Known Unknowns, Unknown Knowns, and Unknown Unknowns of Secondary Metabolism

ABSTRACT Microbial natural products, particularly those produced by filamentous Actinobacteria, underpin the majority of clinically used antibiotics. Unfortunately, only a few new antibiotic classes have been discovered since the 1970s, which has exacerbated fears of a postapocalyptic world in which antibiotics have lost their utility. Excitingly, the genome sequencing revolution painted an entirely new picture, one in which an average strain of filamentous Actinobacteria harbors 20 to 50 natural product biosynthetic pathways but expresses very few of these under laboratory conditions. Development of methodology to access this “hidden” biochemical diversity has the potential to usher in a second Golden Era of antibiotic discovery. The proliferation of genomic data has led to inconsistent use of “cryptic” and “silent” when referring to biosynthetic gene clusters identified by bioinformatic analysis. In this Perspective, we discuss this issue and propose to formalize the use of this terminology.

Experimental Investigation of Dynamic Compression Mechanical Properties of Frozen Fine Sandstone

Aiming at the dynamic mechanical properties of weakly cemented fine sandstone in the rich water-bearing strata in western China under dynamic loading, a 50 mm rod diameter separation Hopkinson pressure bar (SHPB) test was used to study the Paleogene fine sandstone in a coal mine in Ningxia. The system carried out the impact compression tests of −15°C, −20°C, and −30°C and the average strain rate of 28 s−1–83 s−1 and obtained the dynamic compressive strength of the frozen fine sandstone specimens under different test conditions. The strain curve and the fracture morphology were analyzed for the relationship between dynamic peak stress, peak strain, dynamic strength growth coefficient (DIF), and fracture morphology and strain rate. The results show that the peak stress of frozen fine sandstone increases from the decrease of freezing temperature under the same average strain rate. The peak stress of the specimen increases from the increase in the average strain rate of the same freezing temperature. The failure modes of specimen are mainly divided into axial splitting tensile failure and compression crushing failure. To the splitting tensile failure and the compression crushing failure, the main factors determining the two failure modes are the strain rate, while the temperature affects the severity of the impact damage. In the load strain rate and temperature range, the DIF of the frozen fine sandstone is linearly correlated with the strain rate, and the lower the temperature, the slower the growth rate of the DIF.

Identification of modal strains in concrete beams at sub-microstrain amplitude excitation using fibre Bragg grating sensors mounted on a strain-amplifying transducer

Vibration-based damage identification is a non-destructive method that enables the health monitoring of civil infrastructures. It aims to detect the presence and location of damage by measuring changes in the vibration characteristics of these structures. Unfortunately, the most popular vibrational parameters – natural frequencies and modal displacements – have a low sensitivity to certain types of local damage. Modal strains and curvatures, on the other hand, can be sufficiently sensitive to local damage, but monitoring modal strains is challenging. Indeed, the strain amplitudes can be in the sub-microstrain range (<1 με) when considering ambient excitation which is too small for most conventional techniques. Here we show that such measurements can be successfully carried out in a quasi-distributed manner with fibre Bragg grating–based sensors that have been mounted on a dedicated strain-amplifying transducer. First, we report on lab-scale dynamic tests on a 5-m-long concrete beam, equipped with such transducers having a strain amplification of 62. Our results show that we can identify the first three bending modes while the average strain level on the beam was only 0.06 με. Second, we present the first field test for these transducers conducted on a high-speed railway viaduct. We have succeeded to obtain six strain modes of the viaduct from the data collected with fibre Bragg gratings on the transducers at an average strain level of 0.067 με. To the best of our knowledge, this is the first time that strain mode identification in operational conditions using strain-amplifying transducers was successful. This demonstration can be a starting point for the implementation of vibration-based damage identification in civil structures allowing the fulfilment of its long-standing promise.