scholarly journals Effects of residual stresses on the bending stiffness of shafts strengthened by enveloping de-formation

2021 ◽  
Vol 25 (4) ◽  
pp. 412-420
Author(s):  
L. G. Klimova
Keyword(s):  
Residual Stresses ◽  
Testing Machine ◽  
Hydraulic Testing ◽  
Bending Stiffness ◽  
Low Degree ◽  
Bending Resistance ◽  
Part Surface ◽  
Protective Medium ◽  
Cylindrical Parts ◽  
Residual Compression

The aim was to study the effects of technological residual stresses on the bending stiffness of cylindrical parts of shafts and axes. Experiments were conducted for elongated cylindrical specimens made of steel grade 35 with a diameter of 30 mm using boring and turning methods. Specimens were annealed in a protective medium to remove initial residual stresses. Experiments were carried out using an Amsler laboratory hydraulic testing machine and VK8 grade hard-alloy matrices. The experiments showed that, for an extremely low degree of relative crimping of 0.1 to 0.5%, the size of the layer with tangential residual compression stresses gradually decreases. The stiffness of such cylindrical workpieces remains almost unchanged. An increase in relative crimping (from 0.5 to 1.2%) leads to a decrease in resi dual compression stresses on the part surface. The layer thickness with tangential residual compression stresses starts to increase. This leads to a decreased residual buckling and an increased bending stiffness. It was found that the degree of relative crimping has no effect on the variation of distribution depth of axial residual stresses. Optimal distribution of tangential residual compression stresses can be reached by increasing their depth. A linear relationship was found for relative crimping of 0.1 to 1.0%. The highest bending resistance was recorded for specimens strengthened by residual crimping of about 1.0%. By processing workpieces using enveloping deformation with crimping of 0.1% and loading them with a transverse force of 0.6 kN, bending distortion can be decreased and the strength of parts can be increased by 5 times. It was found that the bending stiffness of cylindrical shafts is greatly affected by residual compression stresses. The bedding depth of residual stresses has various effects on the stiffness of cylindrical parts. Thus, correct use of strengthening enveloping deformation can form a high-quality surface layer on parts with the pre-defined distribution of residual stresses.

Using Embossing to Create a Fiber Reinforced Honeycomb Composite

2005 ◽  
Vol 127 (2) ◽  
pp. 257-262 ◽  
Author(s):  
William Jordan
Keyword(s):  
Tensile Strength ◽  
Composite Material ◽  
Carbon Fibers ◽  
Flexural Modulus ◽  
Testing Machine ◽  
Charpy Impact ◽  
Tensile Tests ◽  
Hydraulic Testing ◽  
Charpy Impact Toughness ◽  
Bend Tests

This research project used hot embossing to create a strong and tough polymeric based composite structure. A honeycomb type structure was created by pressing small grooves into thin polycarbonate sheets. A trapezoidal die was used to create hexagonal shaped channels in the polymeric sheet. A number of these sheets were then bonded together to form a composite material. Carbon fibers were embedded into the channels in some of the laminates. The embossing process was carried out at an elevated temperature in an environmental chamber attached to an MTS servo hydraulic testing machine. The grooved structure had a 31% to 45% decrease in the apparent density compared to the ungrooved specimens. Bend tests, tensile tests, and Charpy impact tests were performed on laminates made from this material. The specific values of tensile strength, flexural modulus, and Charpy impact toughness were increased. A small percentage of fibers significantly increased both the stiffness and strength of the laminate.

Designing Hot Working Processes of Nickel Base Superalloys Using FEM Simulation

2001 ◽  
Author(s):  
R. Kopp ◽  
M. Tschirnich ◽  
M. Wolske ◽  
J. Klöwer
Keyword(s):  
Testing Machine ◽  
Fem Simulation ◽  
Material Model ◽  
Hydraulic Testing ◽  
Compression Tests ◽  
Finite Element Program ◽  
Real Process ◽  
Forming Temperature ◽  
Element Program ◽  
Nickel Base

Knowledge of correct flow stress curves of Ni-based alloys at high temperatures is of essential importance for reliable plasto-mechanical simulations in materials processing and for an effective planning and designing of industrial hot forming schedules like hot rolling or forging. The experiments are performed on a computer controlled servo-hydraulic testing machine at IBF (Institute of Metal Forming). To avoid an inhomogeneous deformation due to the influence of friction and initial microstructure, a suitable specimen geometry and lubricant is used and a thermal treatment before testing has to provide a microstructure, similar to the structure of the material in the real process. The compression tests are performed within a furnace, which keeps sample, tools and surrounding atmosphere at the defined forming temperature. The uniaxial compressions were carried out in the range of strain rates between 0.001 and 50 s−1 and temperatures between 950 and 1280°C. Furthermore two-stage step tests are carried out to derive the work hardening and softening behaviour as well as the recrystallisation kinetics of the selected Ni-based alloys. At the end of this work a material model is adapted by the previously determined material data. This model is integrated into the Finite Element program LARSTRAN/SHAPE to calculate a forging process of the material Alloy 617.

scholarly journals Review of Intermediate Strain Rate Testing Devices

Metals ◽  
2020 ◽  
Vol 10 (7) ◽  
pp. 894
Author(s):  
Trunal Bhujangrao ◽  
Catherine Froustey ◽  
Edurne Iriondo ◽  
Fernando Veiga ◽  
Philippe Darnis ◽  
...  
Keyword(s):  
Strain Rate ◽  
Measurement Techniques ◽  
Testing Machine ◽  
Hydraulic Testing ◽  
Manufacturing Processes ◽  
Strain Rates ◽  
General Description ◽  
Intermediate Strain Rate ◽  
Friction Stir ◽  
Rate Testing

Materials undergo various loading conditions during different manufacturing processes, including varying strain rates and temperatures. Research has shown that the deformation of metals and alloys during manufacturing processes such as metal forming, machining, and friction stir welding (FSW), can reach a strain rate ranging from 10−1 to 106 s−1. Hence, studying the flow behavior of materials at different strain rates is important to understanding the material response during manufacturing processes. Experimental data for a low strain rate of <101 s−1 and a high strain rate of >103 s−1 are readily available by using traditional testing devices such as a servo-hydraulic testing machine and the split Hopkinson pressure bar method, respectively. However, for the intermediate strain rate (101 to 103 s−1), very few testing devices are available. Testing the intermediate strain rate requires a demanding test regime, in which researchers have expanded the use of special instruments. This review paper describes the development and evolution of the existing intermediate strain rate testing devices. They are divided based on the loading mechanism; it includes the high-speed servo-hydraulic testing machines, hybrid testing apparatus, the drop tower, and the flywheel machine. A general description of the testing device is systematically reviewed; which includes the working principles, some critical theories, technological innovation in load measurement techniques, components of the device, basic technical assumption, and measuring techniques. In addition, some research direction on future implementation and development of an intermediate strain rate apparatus is also discussed in detail.

scholarly journals Lag-Screw Osteosynthesis in Thoracolumbar Pincer Fractures

2020 ◽  
pp. 219256822094144
Author(s):  
Marc Auerswald ◽  
Philipp Messer-Hannemann ◽  
Kay Sellenschloh ◽  
Jan Wahlefeld ◽  
Klaus Püschel ◽  
...  
Keyword(s):  
Computed Tomography ◽  
Testing Machine ◽  
Axial Loading ◽  
Fatigue Loading ◽  
Biomechanical Properties ◽  
Hydraulic Testing ◽  
Ct Scans ◽  
Follower Load ◽  
Lateral Bending ◽  
Bony Healing

Study Design: Biomechanical. Objective: This study evaluates the biomechanical properties of lag-screws used in vertebral pincer fractures at the thoracolumbar junction. Methods: Pincer fractures were created in 18 bisegmental human specimens. The specimens were assigned to three groups depending on their treatment perspective, either bolted, with the thread positioned in the cortical or cancellous bone, or control. The specimens were mounted in a servo-hydraulic testing machine and loaded with a 500 N follower load. They were consecutively tested in 3 different conditions: intact, fractured, and bolted/control. For each condition 10 cycles in extension/flexion, torsion, and lateral bending were applied. After each tested condition, a computed tomography (CT) scan was performed. Finally, an extension/flexion fatigue loading was applied to all specimens. Results: Biomechanical results revealed a nonsignificant increase in stiffness in extension/flexion of the fractured specimens compared with the intact ones. For lateral bending and torsion, the stiffness was significantly lower. Compared with the fractured specimens, no changes in stiffness due to bolting were discovered. CT scans showed an increasing fracture gap during axial loading both in extension/flexion, torsion, and lateral bending in the control specimens. In bolted specimens, the anterior fragment was approximated, and the fracture gap nullified. This refers to both the cortical and the cancellous thread positions. Conclusion: The results of this study concerning the effect of lag-screws on pincer fractures appear promising. Though there was little effect on stiffness, CT scans reveal a bony contact in the bolted specimens, which is a requirement for bony healing.

Determination of the Residual Stress State of High-Pressure Nozzles During Diamond Smoothing

2020 ◽  
pp. 3-11
Author(s):  
S.A. Zaides ◽  
A.N. Mashukov
Keyword(s):  
Finite Element ◽  
High Pressure ◽  
Stress State ◽  
Residual Stresses ◽  
Element Model ◽  
Depth Of Penetration ◽  
Residual Stress State ◽  
Hardening Treatment ◽  
Cylindrical Parts ◽  
Smoothing Process

The paper presents the results of a study that examines modelling of the polishing and hardening treatment of axisymmetric cylindrical parts such as high-pressure fittings with metal seals on the pipe and the rod. A finite element model of the diamond smoothing process was developed, which allowed one to determine the stress state in the deformation zone depending on the feed rate, tool deflection angle, pressing force, and depth of penetration into the material of the part. The analysis of the modelling results helped to identify a range of optimal modes for diamond smoothing. By using finite element modelling in ANSYS Workbench Mechanical it was possible to test those smoothing modes that were difficult to test experimentally. The study identified the most significant factors that influenced the formation of the maximum values of residual stresses in the surface layer of gate assemblies of high-pressure valves. The maximum values of compressive residual stresses, the value of which did not exceed the yield strength of the material were determined.

Apparatus for strain and load cycling at elevated temperature with high-accuracy control during hold periods

1970 ◽  
Vol 5 (4) ◽  
pp. 284-291 ◽  
Author(s):  
D J White ◽  
G P Horwood ◽  
Z Czajkowski
Keyword(s):  
Load Capacity ◽  
Axial Strain ◽  
Testing Machine ◽  
Cyclic Stress ◽  
Hydraulic Testing ◽  
Gauge Length ◽  
Conic Section ◽  
Accuracy Control ◽  
Load Cycling ◽  
Better Than

A description is given of apparatus which has been developed to determine accurately the cyclic stress-strain behaviour of materials subjected to combined high-strain fatigue and creep at temperatures up to 700°C. The servo-hydraulic testing machine has a load capacity of ±20 000 lbf in push-pull and can operate in either a strain-cycling or a load-cycling mode. The specimen has a diameter of 0.5 in and a parallel gauge length of 1.5 in terminating in conic-section ridges on which extensometers are mounted for the measurement and control of axial strain. Strain is held constant to better than ±1 × 10−5 during hold times of up to 12 h and temperature control is better than ±0.5 degC.

Stable Crack Growth in Ceramics at Ambient and Elevated Temperatures

1993 ◽  
Vol 115 (3) ◽  
pp. 281-285 ◽  
Author(s):  
J. Y. Pastor ◽  
J. LLorca ◽  
J. Planas ◽  
M. Elices
Keyword(s):  
Fracture Behavior ◽  
Elevated Temperatures ◽  
Testing Machine ◽  
Mouth Opening ◽  
Stable Crack Growth ◽  
Hydraulic Testing ◽  
Crack Mouth Opening Displacement ◽  
Zirconia Ceramic ◽  
Opening Displacement ◽  
Stable Crack Propagation

Quasi-static, stable crack propagation tests in ceramics are presented. The tests are performed using a recently developed technique in which the crack mouth opening displacement (CMOD) is continuously monitored during the test by means of a laser extensometer, and this signal is employed to control a servo-hydraulic testing machine. The advantages of such tests to characterize the fracture behavior of ceramics at high temperature are described, and the technique is used to study the fracture behavior of an ytria-partially stabilized zirconia ceramic at ambient and elevated temperatures.

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