Two-Point Bend

Specialists in Mechanical Testing and Reliability of Optical Fibers

Two-Point Bend Tester

Purpose

The 2-point bend test is an extremely convenient technique for determining the strength and fatigue parameters of fibers in general and high strength optical fibers and ribbons in particular. First described by Murgatroyd [ref. 1], the technique is now used extensively in the optical fiber industry. Reference 2 contains a detailed description and evaluation of the method. 2-point bending can rapidly generate large quantities of data for routine strength and fatigue measurements and for evaluating various polymer coatings.

(click photographs for bigger images)

Description

The 2-point bend test involves placing a loop of fiber bent through 180° between two faceplates. The faceplates are grooved to locate the fiber in position. The faceplates are then brought together by a computer controlled stepper motor translation stage. An acoustic detection circuit halts the stepper motor when the fiber breaks. The computer software then calculates the strength from the faceplate separation at failure. The system includes:

	stepper motor controlled translation stage and controller.
	bending hardware for mounting on the translation stage. Includes mounting plates and single grooved faceplates for holding a 250 µm coating diameter polymer coated fiber.
	digital interface designed for connection to the parallel printer port of an IBM PC, PS/2 or compatible. Does not require an expansion slot if the computer's existing printer port is used.
	computer interface unit also contains a digital position readout, manual motor control and acoustic break detector with acoustic transducer.
	software for complete control of the system from an IBM PC or compatible.
	miscellaneous software utilities for statistical analysis of results and data presentation.
	all necessary cables and connectors.

The control software is extremely powerful featuring:

	strength measurement under conditions of constant faceplate velocity, constant strain rate or constant stress rate. (Only the constant faceplate velocity mode is available with 2POINT Direct.)
	incorporates a corrections for the non-linear fiber elastic modulus.
	a static fatigue mode in which the time to failure is determined as a function of the faceplate separation (ref. 3).
	reports strain and stress, faceplate speed, strain rate and stress rate at failure and time to failure and all other key experimental parameters.
	fully configurable by the user both from configuration files and by menus - configurable parameters include fiber dimensions and elastic properties, faceplate gap for loading fiber, speed parameters, screen menu colors etc. etc.
	guaranteed to meet all requirements of current standards (TIA/EIA, IEC, Bellcore/Telcordia, etc.).

Click here for a full description of the 2POINT for Windows control program.

Options

Automatic Fiber Loader: An automatic fiber loader option is available which permits strength and fatigue measurements to be made automatically without operator intervention. Click here for further information.
Polished faceplates: Polished faceplates (FP-POL) are used for testing bare fiber and flat fiber ribbons. (Click the above images for bigger versions.)
Multi-Groove Faceplates

Multi-V-groove faceplates are used for testing up to 12 (FPV-12) or 30 (FPV-30) fibers simultaneously. Note that fibers must be tested one at a time at the highest loading rates, but many can be tested simultaneously at slower loading rates. Total testing time is controlled by the slowest loading rate used so that multi-groove faceplates can greatly reduce testing time when making fatigue measurements for a range of loading rates. (Click the above image for a bigger version.)

For more detailed information on faceplate options click here.
Ruggedized System

An environmentally hardened stepper motor and translation stage constructed of stainless steel is available for testing in harsh environments (TP-8585). The system is guaranteed for use up to 85ºC, 85% humidity (a test environment specified for some standard test procedures).

Translation Stage Movement

The standard system includes a 100 mm travel, 1 µm per step stepper motor/translation stage. Other travels and resolutions are available. Please contact us for further information.

Requirements

The system comes complete except that an PC is needed. Requirements:

2POINT Pro for Windows	Minimum requirement is 500 MHz processor, any version of Windows. Requires a serial or USB port.
2POINT Direct for Windows	Minimum requirement is 1 GHz processor (3 GHz recommended), any version of Windows. Requires an available parallel printer port.
2POINT for DOS	Minimum requirement is a 286 processor running Windows 98 or earlier.

The computer requires a parallel printer port (a serial or USB port is required for 2POINT Pro). A minimum recommended requirement is a 2 GHz PC for 2POINT for Windows (2POINT Direct) but only an i386 processor if needed for 2POINT for DOS.

Specifications

All specifications are for 125 mm glass diameter silica optical fibers. Contact us for information on other fiber sizes.

Maximum loading rate	5 mm/s 50 %/min 500 MPa/s
Maximum displacement (others available)	100 mm
Positioning error (all sources)	< 5 µm

Ordering Information

Description	Part #
Complete 2-point bend system (including all hardware, electronics, cables and software - 2POINT Direct and 2POINT for DOS) ^‡	TP-2
2POINT Pro software and System Controller for new systems or upgrading existing systems^‡	2POINT-P
2POINT Direct upgrade for existing systems^‡	2POINT-D
Ruggedized stainless steel upgrade (guaranteed for 85ºC, 85% humidity operation)^†	TP-8585
Polished faceplates and clamps for bare fibers and fiber ribbons (pair)	FP-POL
V-grooved faceplates for 12 fibers (pair)	FPV-12
V-grooved faceplates for 30 fibers (pair)	FPV-30
Replacement single V-grooved faceplates (pair)	FPV-1

^† must be ordered at the same time as TP-2.^‡ for a description of the 2POINT Pro for Windows and 2POINT Direct for Windows software, please click here.

References

J. B. Murgatroyd, "The strength of glass fibres. Part II. The effect of heat treatment on strength", J. Soc. Glass Tech.28 388-405, 1944.
M. J. Matthewson, C. R. Kurkjian and S. T. Gulati, "Strength measurement of optical fibers in bending", J. Am. Ceram. Soc. 69 [11], 815-821, 1986.
M. J. Matthewson & C. R. Kurkjian, "Static fatigue of optical fibers in bending", J. Am. Ceram. Soc. 70 [9] 662-668 (1987).