A mechanical failure occurs when a mechanical component or system breaks down or stops working as intended. Mechanical failures can occur in many different types of equipment and machinery across a wide range of industries. Some common examples of mechanical failures include:
Engine failure
One of the most familiar examples of mechanical failure is an engine failure. This occurs when some component or system within the engine breaks or malfunctions, causing the engine to stop running properly. Some specific examples of engine failures include:
- Blown head gasket – Head gaskets seal the junction between the engine block and cylinder head. If the gasket becomes damaged, combustion gases can leak out causing loss of engine power.
- Broken timing belt – The timing belt synchronizes the rotation of the camshaft and crankshaft. If the belt snaps, the valve and piston timing will be disrupted, likely causing engine damage.
- Cracked engine block – The engine block is the foundation of the engine. Cracks can allow coolant or oil to leak out of the engine.
- Thrown rod – Connecting rods link the pistons to the crankshaft. If a rod breaks free of the crankshaft, it can punch a hole in the engine block.
- Burned valve – Engine valves can burn and warp if they get too hot. This can lead to compression loss and reduced engine power.
An engine failure can have a range of root causes including lack of maintenance, normal wear and tear, manufacturing defect, or damage from overheating, insufficient oil, or foreign object debris. Engine failure results in the inability to start the engine or loss of engine power.
Drive train failure
The drive train includes all the components that transfer power from the engine to the wheels or tracks on a vehicle. Some examples of drive train failures include:
- Broken driveshaft – The driveshaft rotates power from the transmission to the differential. If it fractures, power cannot be transferred.
- Faulty universal joint – U-joints allow the driveshaft to flex. Worn out u-joints can cause driveline vibration and eventual failure.
- Leaking transmission – Fluid enables the transmission to shift gears. Low fluid levels cause slippage and grinding shifts.
- Tooth shearing in differential – The differential couples the axles together while allowing them to rotate at different speeds. Sheared teeth will disable the differential.
- Broken axle – Axles transfer power to the wheels. A broken axle eliminates power delivery to that wheel.
Common root causes of drive train failures include lack of lubrication, excessive load, or severe impact. The inability to transfer engine torque through the drive train leads to immobilization of the vehicle.
Hydraulic system failure
Hydraulics are commonly used to control machinery. Hydraulic fluid is pumped through valves and cylinders to provide force and motion. Some hydraulic system failures include:
- Pump failure – Hydraulic pumps generate flow and pressure. Worn out pumps cannot provide adequate force.
- Hose leaks – Leaking hoses reduce pressure in the system leading to inadequate force at the cylinders.
- Blown seals – Seals contain the pressurized fluid within the system. Failed seals lead to leaks.
- Sticking valves – Valves control fluid flow and pressure levels. Sticking valves disrupt system operation.
- Air in system – Air bubbles in the fluid can cause hydraulic system components to be sluggish or erratic.
Typical causes of hydraulic failure include contamination in the fluid, excessive pressure spikes, or normal wear on components. The effects of hydraulic failure depend on the specific function the system performs.
Brake failure
The brakes on a vehicle or machine convert kinetic energy into heat through friction to slow or stop movement. Brake failures include:
- Worn brake pads/shoes – Brake pads press against a rotor to slow the vehicle. Excessively worn pads reduce braking power.
- Air in brake lines – Brakes are activated hydraulically. Air in the lines compresses instead of transmitting pressure.
- Grease/oil on rotors/drums – Contamination on braking surfaces greatly reduces friction and braking capability.
- Leaking brake fluid – Loss of brake fluid reduces pressure applied to the calipers.
- Brake fade – Overheated brakes can fade, meaning they lose stopping power until cooled down.
The most common reasons for brake failure are prolonged use without servicing, loss of hydraulic pressure, or overheating. Failed brakes increase stopping distance required to slow or stop the vehicle.
Failure analysis
When a mechanical failure occurs, a failure analysis is often conducted to determine the root cause so it can be prevented in the future. Some steps in a failure analysis include:
- Document damage or defective state – Thoroughly describe and photograph the failure.
- Collect background data – Operating history, maintenance records, repair history, etc.
- Evaluate failed components – Look for damage patterns, wear, corrosion, etc.
- Determine failure sequence – How did one component lead to failure of the next component?
- Identify root cause – Find the initial fault that precipitated the failure.
- Recommend corrective action – Changes to prevent reoccurrence of the failure.
Common tools used during failure analysis include visual inspection, nondestructive testing (e.g. radiography, ultrasound, dye penetrant), mechanical testing, fractography, and microscopy. The end goal is determining a root cause and solution to improve reliability.
Case study: Automotive engine failure
Here is an example of how a failure analysis was used to investigate an engine failure in an automobile:
Background:
- Vehicle make/model: 2010 Toyota Camry
- Mileage: 125,000 miles
- Maintenance history: Regular oil changes, no major repairs
- Failure description: Vehicle suddenly stopped running while driving. Driver reported loud knocking sound from engine.
Failure investigation:
- Disassembled engine for inspection
- Found rod bearing on cylinder 3 was damaged causing the connecting rod to detach from crankshaft
- Rod bearing showed signs of overheating and oil starvation
- Main crankshaft bearings were undamaged
- Oil passages were clear with no blockages
- Oil pump functioning normally
Findings:
- Rod bearing failure caused connecting rod to break free and knock into engine
- Bearing overheated due to lack of oil
- Other engine components were undamaged and functioning properly
Root cause:
Since the oil system was operating normally, the root cause was determined to be a defective connecting rod bearing. The bearing likely had substandard dimensions that led to premature wear and failure.
Corrective action:
- Replaced damaged connecting rod and bearing
- Checked remaining rod bearings as a precaution
This failure analysis identified the specific component failure and root cause, allowing corrective action to be taken to resolve the issue and prevent future engine failures.
Case study: Industrial furnace mechanical failure
Here is a failure analysis example on an industrial furnace:
Background:
- Furnace used for heat treating metals in manufacturing facility
- Furnace temperature not reaching required set point after several hours of operation
- Burners had adequate fuel supply and were functioning normally
- Furnace was approximately 10 years old with average production use
Failure investigation:
- Inspected refractory lining inside furnace chamber – found large crack on side wall
- Crack enabling ambient air infiltration into furnace chamber
- Preventing chamber from reaching required temperature
- Refractory showed signs of erosion indicating gradual wear over time
Findings:
- Cracked refractory lining allowed excess air leakage into furnace
- Air leakage preventing chamber from reaching required temperature
- Refractory wear likely due to age and repetitive thermal cycling
Root cause:
The root cause was determined to be degradation of the refractory lining over time due to repeated high temperature furnace operation cycles.
Corrective action:
- Replaced damaged refractory lining
- Reinforced new refractory during installation to prevent crack formation
- Implemented preventive maintenance to inspect refractory lining periodically
The failure analysis provided critical details to identify the root cause of the temperature issue. By replacing the lining and implementing preventive maintenance, future failures were mitigated.
Conclusion
Mechanical failures can occur in virtually any equipment with moving parts or assemblies. Performing failure analysis enables the root cause to be determined so corrective and preventive measures can be taken. Some examples of mechanical failures include engine failures, drive train breakdowns, hydraulic system leaks, brake problems, refractory degradation, and more. Methodical failure analysis using visual inspection, testing, and other methods can uncover the root causes of the failure like defective components, lack of maintenance, contamination, overheating, or normal wear. Understanding the reasons the failure occurred provides valuable insights to improve the design or operation of equipment and reduce future breakdowns.