Feasibility Study of a Combined Tension-Torsion Hopkinson Bar

The increasing interest to improve the description of the plastic behavior and the fracture prediction for ductile materials under complex loading conditions conducted the researchers to overcome the J2 plasticity theory. To do this more sophisticated plasticity model base on ductile damage have been implemented. Material model parameters must be identified by means of proper testing and calibration procedures requiring different loading conditions. Different types of tests must be performed, imposing multiaxial stress paths to the specimens. Tensile tests on smooth and round notched bars, plane strain tests, torsion tests, compression and combined tension–torsion tests on hollow and solid cylindrical bars must be executed. While multiple works are present in literature for model assessment and validation in quasi-static conditions, nothing can be found at high strain rate in biaxial conditions (tension-torsion). Biaxial tests in dynamic conditions are very difficult to carry out especially if you are interested to register the entire story of stress and strain. In this work, analytical and numerical study to evaluate the feasibility to carry out dynamic tension, dynamic torsion, dynamic torsion-static tension/compression and dynamic tension–dynamic torsion tests is discussed. The tests will be performed using a properly designed Split Hopkinson Bar.

Karakterisasi Ketahanan Lelah Takik Ulir Whitworth Akibat Pembebanan Puntir Dinamis pada Baja Karbon Rendah

This study aims to analyze Whitworth thread's fatigue characterization due to dynamic twisting on low carbon steel. The research method uses experiments with pre-experimental design with the form of intact group comparison. The experimental group was specimens with Whitworth thread notch depth of 0.67 mm, 0.81 mm, and 1.16 mm. The control group was Whitworth threads with a notch depth of 0.9 mm. The study used low carbon steel with a carbon content of 0.12% wt. The dynamic torsion testing with a twisting angle of 5 reveals that the deeper the Whitworth thread notch, the lower the fatigue resistance. The fracture surface is visible due to dynamic torsion in the form of initial crack, crack propagation rate, and final crack.Fenomena kegagalan lelah disebabkan oleh pola pembebanan dan bentuk takikan. Pola pembebanan terjadi karena puntir lentur dan puntir dinamis. Bentuk takikan diperlukan karena tuntutan desain, salah satunya adalah takik ulir whitworth. Penelitian ini bertujuan untuk menganalisis karakterisasi ketahanan lelah ulir whitworth akibat pembebanan puntir dinamis pada baja karbon rendah. Metode penelitian menggunakan eksperimen dengan pre-experimental design dengan bentuk intact-group comparison. Kelompok eksperimen adalah spesimen dengan kedalaman takik ulir whitworth 0.67 mm, 0.81 mm, dan 1.16 mm. Kelompok kontrol dengan kedalaman takik ulir whitworth sebesar 0.9 mm. Penelitian menggunakan baja karbon rendah dengan kandungan karbon sebesar 0.12% wt. Hasil pengujian puntir dinamis mengungkapkan bahwa semakin dalam takik ulir withworth maka ketahanan lelahnya semakin menurun. Bentuk penampang patah akibat pembebanan puntir dinamis berupa initial crack, crack propagation rate dan final crack.

P971 The echocardiographic phenotype in patients with cardiac amyloidosis and heart failure with preserved ejection fraction

BACKGROUND New echocardiographic phenotypes of heart failure (HF) are focused on myocardial systolic involvement of the left ventricle (LV), either endocardial and/or transmural. PURPOSE. To study the pattern of myocardial involvement in patients (p) with HF with preserved left ventricular ejection fraction (pLVEF) and cardiac amyloidosis (CA). METHODS. Comparative study of 16 p with CA and HF with pLVEF, considering as cut point LVEF > 50%, in NYHA class ≥ II / IV, and a control group of 16 healthy people. Longitudinal Strain (LS) and Circumferential Strain (CS) were calculated using 2D speckle-tracking echocardiography, along with Mitral Annulus Plane Systolic Excursion (MAPSE) and Base-Apex distance (B-A). Also, the following indexes were calculated: Twist (apical rotation + basal rotation, º); Classic Torsion (TorC): (twist/B-A, º/cm); Torsion Index (Tor.I): (twist/MAPSE, º/cm) and Deformation Index (Def.I): (twist/LS, º). We suggest the introduction of these dynamic torsion indexes as Tor.I and Def.I that include twist per unit of longitudinal systolic shortening of the LV instead of using TorC which is the normalisation of twist to the end-diastolic longitudinal diameter of the LV. RESULTS There were no differences of age between the groups (68.2 ± 11.5 vs 63.7 ± 2.8 years, p = 0.14). Global values of LS and CS were lower in p with CA indicating endocardial and transmural deterioration during systole, while TorC and Twist of the LV remained conserved in p with CA. However, there is an increase of dynamic torsion parameters such as Tor.I and Def.I that show an increased Twist per unit of longitudinal shortening of the LV in the CA group (Table). CONCLUSIONS In p with CA and HF with pLVEF, the impairment of LS and CS indicates endocardial and transmural systolic dysfunction. In these conditions, LVEF would be preserved at the expense of a greater dynamic torsion of the LV. Table LS (%) CS (%) Twist (º) TorC (º/cm) Tor.I (º/cm) Def.I (º/%) CA pLVEF (n = 16) -11.7 ± 4.2 17.2 ± 4.8 19.8 ± 8.3 2.5 ± 1.1 27.7 ± 13.5 -1.8 ± 0.9 Control Group (n = 15) -20.6 ± 2.5 22.7 ± 4.9 21.7 ± 6.1 2.7 ± 0.8 16.4 ± 4.7 -1.0 ± 0.3 p < 0.001 < 0.01 0.46 0.46 < 0.01 < 0.01 Dynamic Torsion Indexes and Classic Torion Parameters in pLVEF CA patients vs Control group.