Bend Tests

Bend Testing

Several of our tensile test machines are fitted with drive systems, which enable cyclic-bend fatigue testing. These machines can be configured with various sheaves at various locations to simulate a multitude of rope and cable handling systems. We, literally, have hundreds of sheaves in our inventory that can be used, although custom sheaves can be built if necessary. These machines use servo-controlled hydraulic cylinders to apply tension and hydraulic motors or cylinders to supply the drive force. As with tensile tests, auxiliary instrumentation is often used to measure various mechanical, electrical, and optical properties during the test, and the data is graphically displayed and digitally recorded real time by our custom data acquisition system. A general list of our Bend-Over-Sheave (BOS) test machines and their typical capacities is presented below.

 

Machine Tensile
Capacity / lbf
Sheave
Diameter, inches
Bed
Length, feet
Stroke
Length, feet
BOS1 200,000 20-120+ 60 40
BOS2 20,000 4-24 18 18
BOS3 90,000 20-120+ 125 120
BOS5 20,000 4-18 26 26
BOS 6/7 50,000 4-24 8 8
BOS 9/10 12,500 4-11 120 120
BOS 11-14 2,500 2-12 8 8

 

Specialized Tests and Terms

Short-Stroke Bend Testing - A section of cable stays on the sheave with each stroke typically simulating wrap/unwrap of cable on over-boarding sheave as ship pitches and heaves in response to sea state (systems with motion compensation may require long-stoke testing).

Long-Stroke Bend Testing - A section of cable passes completely over the sheave with each stroke simulating deployment/retrieval of the cable over a sheave, fairlead, or winch.

Reverse Bend Tests - A section of cable is subjected to two regular bends where the first bend deforms the cable to one side of the cable axis and a second bend deforms the same section of cable to the opposite side of the cable axis. Typically two general methods are employed to achieve a reverse bend, either a three-sheave trolley that is driven along the test specimen is used to achieve reverse bends or 4-6 sheaves are fixed on the machine and the specimen is driven over the sheaves.

Rigid Body Deployment Test - Specimen has a rigid body inline with the cable or rope. Inboard and outboard tensions are monitored to determine the “sheave factor” (an amplification of cable tension on one side of a sheave due to the cantilevered rigid body on the other side of the sheave).

Traction or Locked Sheave Test - The test sheave is either driven to oppose the drive system or simply locked. These tests are often used to determine the static and dynamic coefficient of friction between a cable and sheave.

Dynamic Umbilical Flex Fatigue Test - Test machine has a driven swing arm on one end that pendulates back-and-forth. The bend diameter is dependent on the bending stiffness of the specimen. These machines are often used to test termination or hard-mounted bend stiffeners. See information in the Dynamic Flexure page for more details.

Traction or Locked Sheave - The test sheave is either driven to oppose the drive system or simply locked. These tests are often used to determine the static and dynamic coefficient of friction between a cable and sheave.