Design of Reinforced Hoses

Technical Challenge

A high-strength reinforced hose failed in service under normal operating conditions well before its intended design life.  Inspections of the subject hose revealed that failure was mainly due to delamination.  The hose is composed of numerous layers; some are plain elastomers while others are reinforced with stiffer metals or polymer fibers of varying wrap angles, fiber pitch, and properties.

The hose elongation response, internal stresses, and torque balance were critical in identifying the cause of delamination and, ultimately, in redesigning the hose to meet performance requirements.

Veryst measured stress-strain data for both the reinforced and plain elastomer hose materials and determined that an assumption of hyperelasticity of the elastomer matrix materials was insufficient.  Veryst therefore calibrated proprietary material models (UMATs) that captured the large strain rate dependent anisotropic behavior, including damage. 

Figure 2 shows the stress-strain behavior of one of the elastomeric layers. 

Veryst then modeled the hose using two nonlinear finite element models: 

1. Macro scale model to predict load elongation, torque balance, effect of internal fluid, and load-carrying capacity.  This model (see Figure 1, above) included all hose layers and modeled the reinforcing fibers using embedded truss/beam elements.  The model also accounted for the additional stiffness caused by the incompressible fluid in the hose.
    
2. Micro scale model to predict local stresses and strains around individual fibers and identify conditions for delamination  (see Figure 3).

Figure 4 shows the specimens used for testing the tensile and compressive response of one of the polymer reinforced layers.

Veryst improved the client’s ability to design for hose elongation response and torque balancing, while improving the client’s understanding of the cause of hose delamination, burst, and rupture.  Additionally, the model provided predictive ability for the hose bending stiffness and elongation.

The overall result was that the client was able to optimize its design with confidence and identify potential failure modes, without costly and time-consuming prototyping and testing of many of the candidate designs.  The client was also able to evaluate quickly alternative hose designs and prepare more accurate performance specifications.