The impact tension behaviors of one layer plain woven carbon epoxy composite:

Part I- Review on Hopkinson

By: 木塔西Presented to: Professor Gu Bohong

Introduction …Hopkinson Summary of literature Review Future work References

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Contents :

The Hopkinson Pressure Bar was first invented by Bertram Hopkinson in 1914[1] as a way to measure stress pulse propagation in a metal bar.

Later, in 1949 H. Kolsky[2] presented an apparatus now known as the split-Hopkinson bar, to measure stress and strain.

For compression testing, two symmetrical bars are situated in series with the sample in between.

The incident bar is struck by a striker bar during testing. The striker bar is fired from a gas gun.

The transmitted bar collides with a momentum trap (typically a block of soft metal). Strain gages are mounted on both the incident and transmitted bars.

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Introduction:

Most modern setups use strain gages on the bars to measure strains caused by the waves.

Assuming deformation in the specimen is uniform, the stress and strain can be calculated from the amplitudes of the incident, transmitted, and reflected waves.

Tension testing in a Split Hopkinson Pressure Bar (SHPB) is more complex due to a variation of loading methods and specimen attachment to the incident and transmission bar .

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The first tension bar was designed and tested by Harding et al. in 1960[3] the design involved using a hollow weight bar that was connected to a yoke and threaded specimen inside of the weight bar.

Another breakthrough in the SHPB design was done by Nichols [4] who used a typical compression setup and threaded metallic specimens on both the incident and transmission ends, while placing a composite collar over the specimen.

Nichols[4] setup would create an initial compression wave by an impact in the incident end with a striker, but when the compression wave reached the specimen, the threads would not be loaded. 

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History:

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Year/ Researcher

Materials

Properties studied

Conditions being used

Testing method

Comments

1914Hopkinson[1]

Metal A Method of Measuring the Pressure Produced in the DetonationImpact of Bullets

A technique to measure the shape of a stress pulse in a longelastic bar

Hopkinson First method, to measure transient impact

1949Kolsky[2]

Rubbers, plastics and metals

Compression and recovery characteristic of materials

A method of the stress-strain relation of materials when stresses are applied for times of the order of 20 microseconds

Hopkinson pressure bar

Perspex recovered almost as soon as the stress was removed, rubbers and polytheneshowed delayed recovery, and copper and lead showed irrecoverable flow

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Year/Researcher

Materials Properties being studied

Conditions being used

Testing method

Comments

1960Harding[3]

Aluminum alloy

obtain reliable stress strain

curves in tension at

impact rates of loading

Designed to give accurate stress-strain curves in tension at strain rates of the order of 1000 per second

SHP Use for high strain rate effect of materials

1981Nicholas[4]

Aluminum,

Titanium, and Steel

alloys

Strain rates up to 1000/s in tension

Modified the split Hopkinson bar or Kolsky

apparatus

Hopkinson use to measure the mechanical properties of material of high strain rat

1985Ruiz[5]

Charpy specimens,

HPB) provides an alternative method……

Hopkinson pressure bar

HPB to improve material fracture strength

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Year Materials Properties being studied

Conditions being used

Testing method

Comments

1990Staab, Gilat[6]

7075-T651 aluminum

The effect of

specimen geometry (length to diameter

ratio)

The dimensions of the apparatus used here allow for test durations of 500 µs

direct-tension split-Hopkinson-bar

Direct-tension split Hopkinson bar apparatus has been introduced

2000Mahfuz, Gary[7]

Foam core sandwich composite

sglass fiber

epoxy matrix

composite

High strain rate

responseof

sandwich composite

s

Strain rates ranging from quasi-static to 1000 /s

SHP Modify the Hopkinson pressure

2003Meng[8]

Metallic pad Copper pad

Mechanical properties of materials under high strain rates

Finite element simulations of wave propagation on the .parametersaffecting wave dispersion.

Hopkinson barfinite

element

simulation

The correlation coefficient of stress waves and numerical simulation, and accurately derived material impact performance.

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Year/Researcher

2000Masaaki Itabashi[9]

Materials Properties being studied

Conditions being used

Testing method

Comments

2001J. H. HWANG[10]

Carbon/EpoxyComposite

Interlaminar Fracture Toughness of Carbon/EpoxyComposite Materials

interfacial ply orientations, α (0◦, 45◦ and 90◦)

width-tapered double cantilever beam (WTDCB) andend-notched flexure (ENF)

The interlaminar fracture behaviors for carbon/epoxy composite materials have

Carbon epoxy material Review summary:

Future work: - Further literature Review - Prepare samples

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References:1.Hopkinson B. A method of measuring the pressure produced in the detonation of high explosives of by the impact of bullets. Philosophical Transactions of the Royal Society of London Series A, 1914, 127(213): 437-4562. Kolsky H. An investigation of the mechanical properties of materials at very high rates of loading. Proceedings of the Physical Society, London, 1949, 62(11): 6763. Wang CY and Xia YM. Validity of one-dimensional experimental principle for flat specimen in bar-bar tensile impact apparatus. International Journal of Solids and Structures, 2000, 37(24): 3305-33224.Harding J, Wood E and Campbell JD. Tensile testing of materials at impact rates of strain. Journal of

Mechanical Engineering Science, 1960, 22(2): 88-965.Nicholas T. Tensile testing of materials at high-rates of strain. Experimental Mechanics, 1981, 21(5): 177-1856.Ruiz C. The hopkinson pressure bar: an alternative to instrumented pendulum for charpy tests. International Journal of Fractures, 1985, 29(2): 101-1097.Staab GH. A direct tension split hopkinson bar for high-strain rate testing. Proceedings of the 1990 SEM Spring Conference on Experimental Mechanics. Bethel, 1990, vol. 31: 583-588.Mahfuz H, Mamum W, Haque A, Mohamed H, Jeelani S. An innovative technique for measuring the high strain rate response of sandwich composites. Composite Structures, 2000,9. Masaaki Itabashi*, Carbon content e!ect on high-strain-rate tensile properties for carbon steels10.J. H. HWANG, Effect of Crack Propagation Directions on the Interlaminar Fracture Toughness of

Carbon/Epoxy Composite Materials

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