Compression tensile tests were performed on SLS samples printed in transverse (H) and parallel (V) direction.

Compressive Eng.stress and Eng.strains have positive values. 

Three different testing equipment were used depending on the strain rate range.
	o Universal testing machine INSTRON 3384: Low strain rates (2.8E-3 to 2.8E-1 s-1)
		- Data directly obtained from the machine measurements.

	o Gleeble 3800 GTC: Middle strain rates (1 to 10 s-1)
		- The machine outputs force in kgf, true stress (MPa) and true strain values. The force, extension and eng stress and strain shown in the .csv files have been obtained from the raw true stress strain values from the machine output. Raw data in .txt files.

	o Hopkinson Split Pressure Bar (HSPB): High strain rates (up to 906 s-1)
		- The calculation of eng. stress and strain is a complex process explained in the following lines:

Hopkinson split pressure bar setup: Projectile, Incident bar and Output bar, and strain gauges attached at the middle length of the bars.
The projectile is fired by compressed air at different pressures to obtain different strain rates.

Instrumentation:
	Ga = 200 - incident output bar gage factor
	Gb = 3000 - output bar gage factor
	Vo = 7.65 - bridge output voltage
	k = 2.18 - k factor
Bars:
	v	0.3 - Poisson's ratio
	E	185 - elastic modulus of bars (GPa)
	ro	8000 - bar density (kg/m^3)
	Co	4808.8 - speed of sound through the bars (m/s) --> co=sqrt(E/ro)
	D	25.4 - diameter (mm)
	Ab	506.7074791 - bar cross section area (mm^2)

Eng.sress and Eng.strain are obtained through a long calculation process.

The experimental data outputs is acquired by the excitation voltage of the strain gauges from the incident (Ch1) and output bars (Ch2), obtaining the raw data as: 

	time(s)	Ch1(V)	Ch2(V)

The voltage variations of the incident (Vi) and reflected (Vr) strain pulses are recorded through Ch1 and Ch2 the transmitted pulse (Vt) as volts. The strain pulses are calculated as:

	ei=2/(1+v)*Vi/K/Vo/Ga
	er=2/(1+v)*Vr/K/Vo/Ga
	et=2/(1+v)*Vt/K/Vo/Gb

The velocities of both sides of the samples are:
	Va=Co*(ei-er)
	Vb=Co*et

Where the engineering strain is obtained as:

	Eng.strain= integral through time [(Va-Vb)/lo] dt 	--> lo is the specimen initial length

And engineering stress is obtained as:
	
	Eng.stress=(Ab*E*et)/Ao --> Ao is the specimen initial cross section


