Erosion equipment

Locations: Building 13 room 1035

Erosion is an energetic process in which one or more particles, microjets, or droplets strike a surface, resulting in irreversible material change. Under high-energy conditions, erosion can lead to immediate plastic deformation or surface cracking. By contrast, continuous and repetitive low-energy impacts may give rise to a fatigue-type mechanism, whereby the surface initially exhibits no visible damage but progressively accumulates subsurface degradation. Once a critical threshold is reached, this damage manifests as measurable material loss and surface wear.

The erosion facility comprises three experimental rigs:

• air-sand erosion rig – airborne particulate erosion up to 300 metre per second (m/s)
• slurry jet erosion rig – waterborne particulate erosion
• cavitation erosion rig – cavitating bubbles create microjet that impinge at hundreds of metres per second.

Air-sand erosion rig

The air–sand erosion test rig is a custom-built facility that was formerly located at the Chilworth site and has recently been relocated to the Highfield Campus. Owing to the high velocities generated as the airflow passes through the venture, the test chamber is enclosed within an acoustic chamber to mitigate noise hazards. All researchers and consultants are therefore required to wear hearing protection during operation.

The rig comprises a compressed air supply capable of delivering the large volumetric flow rates required for testing. Air is directed to the test chamber via a flow meter and a venture, which enables the controlled introduction of erosive particles (erodents). The erodent feed rate is regulated using a vibratory hopper, and particles are accelerated towards the target specimen through a one-metre-long delivery tube. Impact velocities ranging from approximately 30 m/s to 300 m/s can be achieved.

Silica sand is the most commonly used erodent, although alumina, diamond, and glass beads have also been employed. Discrete impact angles of 15°, 30°, 45°, 60°, and 90° are available, with particle sizes ranging from below 100 micrometre (µm) to 2 millimetre (mm).

The rig was originally described in the paper "Design and performance of a high velocity air–sand jet impingement erosion facility".

 

Slurry jet erosion rig

The impact rig was designed at the University and manufactured by Safire and Associates.

It is a pneumatically powered system supplied by the laboratory air lines. The air supply is connected to a valve and pressure gauge that regulate the pressure within an accumulator, which stores a defined volume of compressed air prior to release by a rapid‑acting valve electronically triggered via a foot pedal.

The accumulator is connected to a smooth‑bored barrel, manufactured by a gunsmith to ensure a near gas‑tight seal with the projectile. The barrel is mounted on dual gimbal assemblies, allowing precise adjustment of elevation and direction. Two light gates positioned near the muzzle record the projectile exit velocity. The projectile is typically a 9 mm diameter ball; unhardened balls are preferred, as hardened variants tend to shatter on impact.

The projectile is fired into a test chamber designed to safely contain the impact energy. The chamber is enclosed by two removable 10 mm thick Perspex panels, enabling visualisation of the impact event, including high‑speed imaging. Safety micro‑switches prevent firing unless the panels are correctly installed.

For doctoral research, the rig was adapted to incorporate a plunger system for generating high‑velocity water slugs. By varying the projectile energy and nozzle geometry, slug velocities exceeding 200 m/s have been achieved. The slug formation, velocity, and surface impact are analysed using ultra‑high‑speed imaging at up to five million frames per second.


 

Cavitation erosion rig

The cavitation erosion rig is a custom-built facility that employs an ultrasonic horn to induce the formation of cavitation bubbles within a liquid medium. These bubbles subsequently collapse at the test surface, generating supersonic microjets that cause material removal beneath the horn. This configuration is referred to as indirect cavitation.

The rig operates in accordance with ASTM G32 and functions at a frequency of 20 kilohertz (kHz) with a peak-to-peak displacement amplitude of 50 μm. The vibration amplitude is calibrated using a Keyence high-speed, high-accuracy CCD laser displacement sensor, ensuring precise and repeatable test conditions.
Experiments may be conducted in distilled water to investigate pure cavitation erosion, or in salt water to study combined erosion–corrosion effects. Standard cavitation specimens are square samples measuring 25 mm × 25 mm with a thickness of 5 mm.

Alternative sample geometries or dimensions may be accommodated; however, prior consultation is required, as modifications to the sample holder or test configuration may be necessary.