Effect of Acceleration Pulse Shape on Damage of the Specimen under Hopkinson High-g Loading
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Abstract:
Based on the free Hopkinson pressure bar high-g loading technique, the pure cylindrical lead was mounted on the end section of the incident bar as a specimen to obtain the change law of the axial strain with the shape of acceleration pulses. Both the experimental tests without using pulse shaper and numerical simulations under sine-shaped acceleration pulses were performed and axial strain of the specimen was measured. Results revealed that the shape of acceleration pulse shows highly effect on the damage of the specimen. The axial strain of the specimen arises linearly with the increasing of the acceleration peaks whose durations are all 17μs; while, due to the complexity of plastic wave propagation, 135μs is a critical duration at which axial strain reaches to the maximum under the condition of different durations. The final axial strain of the specimen is determined by both the stress level and stress increment in every time step.Keywords:
Split Hopkinson Pressure Bar
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Based on AMESim, by the analysis of the Conveyor Belt four discrete model, Select and built the Kelvin-Voigt model which is simple and applicable, by comparative analysis of drawing on four commonly used to start the acceleration (uniform acceleration, triangle acceleration, trapezoidal acceleration and the Harrison), Select the Harrison speed as the starting acceleration and Using AMESim to establish the starting model of acceleration.
Belt conveyor
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Split Hopkinson Pressure Bar (SHPB) has become a frequently used technique for measuring uni-axial compressive stress-strain relationship of various engineering materials under high strain rates. The pulse shape generated in the incident bar is sensitive to the length of the striker bar. In this paper, a finite element simulation of a Split Hopkinson Pressure Bar is performed to estimate the effect of varying length of striker bar on the stress-strain relationship of a material. A series of striker bars with different lengths, from 200mm to 350mm, are employed to obtain the stress-strain response of AL6061-T6 in both simulation and experiment. A comparison is made between the experimental and the computed stress-strain curves. Finally the influence of variation of striker bar length on the sample's stress-strain response is presented.
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The use of microprocessors for calculation of dynamic quantities such as speed and acceleration on land based test vehicles which use wheel pulse generating probes is discussed. Methods of pulse prediction and windowing are presented along with formulas for determining the existance of the next pulse. Considerations in actual implementation of a microprocessor for these tasks are brought out.
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The mechanical properties of materials change depending upon the strain rate that
they are subject to. Robust models that capture the materials response at different
strain rates are important. High strain rates from 100s‐1 to 10000s‐1 are undergone in
impact applications. The most widely used method to characterise materials at high
strain rates is the Split Hopkinson Pressure Bar (SHPB).
This project deals with the set‐up and calibration of a Split Hopkinson Pressure Bar for
the dynamic testing of metallic materials at high strain rates. The features of the
equipment needed are discussed, as well as the instrumentation and the connections
between the different components. A calibration routine is also presented in this text.
A finite element analysis of a SHPB calibration test has been performed with LS‐DYNA.
The model consists of two bars put together and does not include a specimen. The
time dependent strain and stress pulses obtained are very well correlated to the
theory. The results from a calibration test in the laboratory at Cranfield University are
also presented. It is observed that the level of accuracy of the finite element model is
better than that of the experimental calibration test.
A complete analysis of a SHPB with a metallic specimen is also performed with finite
elements in LS‐DYNA. The results achieved are extremely close to those predicted by
some hand calculations. The creation and application of a routine with Matlab that
corrects the dispersion effect in the model is a key point to increase the accuracy of
the results. The dispersion correction routine consists of a technique that enables to
filter out the high frequency components of the sampled signal; therefore, part of the
noise is removed. This is performed after the time domain data is converted into the
frequency domain, after using the Fast Fourier Transform. This routine has also been
applied to the experimental results obtained through the calibration test.
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To solve the overshoot of acceleration of traditional model,a model with variable desirable distance for vehicle following is presented,which considering limitation of the acceleration.The linear stability theory is applied to the proposed model,the result of stability is different from the Bando′s.Through the simulation result,it is found that when the maximum acceleration is reasonable,the stability of the traffic flow is better with the increase of the value of maximum acceleration.While the traffic flow becomes unstable when the maximum acceleration is too large.The proposed model is favorable to keep the traffic flow stable.
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Split Hopkinson Pressure Bar
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