Details

Introduction
In a modern aircraft engine, the low-pressure (LP) shaft is one of the most stressed and unforgiving components in the whole machine. It must transmit huge amounts of torque, survive rapid transients, and endure millions of load cycles at elevated temperatures—often for thousands of ours—without a single crack propagating to failure. If that shaft fails in service, you are not talking about a minor inconvenience; you are talking about a serious safety event and a grounded fleet.

The LP Shaft Torsion Fatigue Testing Machine is built specifically to prevent that scenario. It is a full-scale endurance rig that twists, pulls and heats the LP shaft in a way that closely mimics engine reality, but under controlled laboratory conditions. By combining torsional loading, axial tension and a steep thermal gradient, the rig exposes the shaft to a harsher-than-service environment so that weaknesses show up on the test bench—not in the air.

Instead of relying only on calculations and small coupon tests, this machine lets engineers run long-duration, high-frequency fatigue programs on the actual shaft geometry. Every cycle of torque, every degree of twist and every degree of temperature is measured, logged and traceable, so design changes and material choices can be backed by real, hard data.

Key Functional Capabilities
Combined loading on full-length LP shaft
  • Programmable torsional loading from zero up to the required major torque, with a superimposed minor cycle.
  • Axial loading at several discrete force levels, up to the maximum specified axial load.

Thermal gradient simulation
  • Controlled temperature gradient along the shaft, typically from around 100 °C to 350 °C, maintained for the entire duration of the test.

High-cycle fatigue operation
  • Minor torque cycles applied in the high-frequency range (10 Hz class), with each major cycle consisting of many minor cycles and overall testing extending to very high total cycle counts.

Real-time monitoring and control
  • Continuous measurement of torque, axial force, twist angle, displacement, temperature, pressure, vibration and cycle count, with closed-loop control of
servo valves and heaters.

System Architecture – Overview
The machine is built around four main subsystems:
Mechanical test bench
  • Heavy MS base frame with integrated bearing blocks and torsion arm.
  • Adjustable bearing supports to accommodate a range of LP shaft lengths and bearing positions.
  • Full-length insulated canopy enclosing the shaft and heaters, with access doors for mounting and inspection.

Hydraulic actuation
  • Hydraulic power pack with stainless steel tank and electric motor driving a dual vane pump, providing both high-pressure and low-pressure circuits for
dynamic actuation and auxiliary functions.
  • One torsion cylinder coupled via a torsion arm to the shaft, plus two axial cylinders providing tensile loading from both ends.
  • Digital servo valve for torsional control and directional/proportional valves for axial circuits, with filtration and cooling sized for long endurance tests.

Thermal simulation system
  • Multiple band heaters arranged in zones along the shaft to generate and hold the target gradient.
  • Insulation shields and outer cover to minimize heat loss and protect surrounding structure.

Control, SCADA & data acquisition
  • Industrial PLC with dedicated control panel and 27" operator console.
  • SCADA PC recording all channels at fast sampling intervals, with Ethernet connectivity for remote monitoring on the local network.

Technical Specifications

  

    
Category
    
Parameter
    
Typical Value / Capability
  

  

    
Unit Under Test
    
Shaft type
    
Low-pressure aero-engine shaft assembly
  

  

    

    
Overall shaft length
    
Around 1.6–2.0 m (adjustable support positions)
  

  

    
Mechanical Loads
    
Major torque range
    
Programmable into the multi-kNm range for full-scale testing
  

  

    

    
Max torque capability
    
Sized above required test torque for high-cycle endurance
  

  

    

    
Axial load levels
    
Multiple tensile load levels, up to several tens of kN
  

  

    

    
Minor cycle frequency
    
High-frequency (~10 Hz) minor cycles
  

  

    
Thermal Conditions
    
Temperature gradient
    
Approx. 100–350°C along shaft length (zoned control)
  

  

    

    
Heating arrangement
    
Multiple band heaters (several kW) with independent zone control
  

  

    
Hydraulic Power Pack
    
Tank volume
    
~250 L (SS construction with baffles)
  

  

    

    
Motor rating
    
~7.5 kW, driving dual-vane pump set
  

  

    

    
Pump 1 (high pressure)
    
High-pressure section ~200 bar
  

  

    

    
Pump 2 (low pressure)
    
Low-pressure section for make-up/auxiliary circuits
  

  

    

    
Filtration
    
Multi-stage pressure & return filtration
  

  

    

    
Cooling
    
Oil-to-water heat exchanger
  

  

    
Hydraulic Actuators
    
Torsion cylinder
    
Double-acting cylinder delivering torque via torsion arm
  

  

    

    
Axial cylinders
    
Two double-acting cylinders applying axial pull from both ends
  

  

    
Servo & Valves
    
Servo valve
    
Digital servo-proportional valve with ±10 V command
  

  

    

    
Pressure control valves
    
Proportional relief & pressure control valves
  

  

    
Instrumentation
    
Torque sensor
    
High-accuracy reaction torque transducer
  

  

    

    
Axial load cell
    
Tension/compression cell, located outside hot zone
  

  

    

    
Temperature measurement
    
Multiple thermocouples/RTDs along shaft & structure
  

  

    

    
Pressure & vibration
    
Pressure transmitters & accelerometers
  

  

    
Control & DAQ
    
PLC system
    
Industrial PLC with full interlocks & closed-loop control
  

  

    

    
Operator console
    
27″ console with annunciators, switches, USB & Ethernet
  

  

    

    
Data logging rate
    
Fast sampling (tens of milliseconds)
  

  

    
Overall Rig Envelope
    
Approx. rig length
    
~4.0–4.2 m overall (with canopy & frame)
  

  

    

    
Height / width
    
~1.5–1.7 m high, ~1.0 m wide
  



Operating Workflow – At a Glance
1. Shaft mounting & alignment
  • Install the LP shaft using dedicated adaptors at both ends.
  • Adjust bearing supports along the base frame to match the shaft’s geometry and lock them in position.

2. System checks
  • Fill and de-aerate the hydraulic circuit, verify tank level, filters and cooling water.
  • Check operation of heaters, thermocouples, pressure transmitters, torque sensor, load cells and vibration channels.

3. Profile configuration
  • Define major torque, minor cycle amplitude, axial load level, test frequency, number of cycles and temperature set-points using the SCADA interface.
  • Set abort thresholds for maximum torque, force, temperature and vibration.

4. Test execution
  • Heat the shaft to the required temperature distribution and stabilize the gradient.
  • Apply the axial load and then ramp in the major torque.
  • Superimpose minor torque cycles at the defined frequency for each major cycle.

5. Monitoring and logging
  • Observe live plots of torque, twist, force, displacement, temperature and vibration on the 27" console.
  • All channels are logged continuously for the full duration of the test run for post-processing and fatigue life assessment.

6. Shutdown and inspection
  • At the end of each block of cycles, the rig unloads and cools down in a controlled manner.
  • The shaft can be inspected for crack initiation and growth before the next test increment.

Safety and Protection Highlights
Multi-layer safety interlocks
  • Emergency stop buttons on console and near the rig.
  • Guarding around rotating and hot parts, with interlocks where required.

Hydraulic and electrical protections
  • Over-pressure protection with relief and proportional pressure-relief valves.
  • Standard motor and power protections: over-current, short-circuit, phase failure, overload relays.

Condition-based abort logic
  • Automatic test abort on overshoot of torque, force, temperature or excessive vibration, with events logged in SCADA for traceability.

Fail-safe servo configuration
  • Servo valve and hydraulic circuits designed to move to a safe state on power or signal loss.

Summary
In practice, this rig is the place where an LP shaft either proves itself or fails under controlled conditions. It delivers full-scale torsion, axial and thermal fatigue in one integrated package, with the accuracy and repeatability needed for aero-engine certification work. For anyone responsible for shaft integrity—design, materials, testing or certification—this machine is the backbone of a serious fatigue validation program.