What causes mechanical damage?

Mechanical damage refers to physical harm done to an object due to the application of force. It can occur in many ways and lead to issues like wear, tear, fractures, deformations, and more. Understanding what causes mechanical damage is important for preventing and mitigating it.

Table of Contents

Common Causes of Mechanical Damage

There are several common causes of mechanical damage:

Impact – A sudden collision or blow from an object can cause dents, cracks, chips, or other damage. Dropping, bumping, or striking an item are examples.

Stress – Forces that pull, twist, or otherwise strain an object. This stress can cause deformations, fractures, or breaks over time.
Abrasion – Rubbing and friction wears away surface layers through sanding, grinding, erosion, or other abrasive actions.
Fatigue – Repetitive forces like vibration or cyclic loading causes material weakening and eventual failure.

Corrosion – Environmental factors like water, air, and temperature corrodes and degrades materials.
Wear – The gradual loss of material through consistent use causes erosion, pitting, thinning, or wiping away of surfaces.

These forces act upon objects through normal use, accidents, inadequate maintenance, manufacturing defects, improper design, and more. Understanding the root cause of damage is key for prevention.

Impact Forces

Sudden impact forces are a very common source of mechanical damage. The degree of damage depends on:

Mass – Heavier objects impart more force during impacts.
Acceleration – Faster moving objects hit with greater force.

Composition – Brittle materials like glass are more prone to fractures and cracks. Ductile materials like metals deform and dent.
Geometry – Impact points and shape effects resulting stresses.
Energy – Kinetic energy gets dissipated as damage during the impact.

Examples of impact damage include:

Dents and deformations from dropping equipment, tools, parts, etc.
Chips, cracks, or shattering in materials struck by objects.

Breaks or fractures from collisions with other equipment.
Pitting or gouging from high velocity particle impacts.
Crushing, compacting, or flattening when crushed by high force.

Controlling the operation of machinery, handling/transport methods, and environment are key to mitigating impact damage. Use of padding, barriers, and dissipation methods further reduce damage when impacts occur.

Stress Forces

When an object is put under structural stress, it can cause mechanical damage over time or reach sudden breaking points. Stress includes:

Tension – Pulling forces that stretch and elongate objects.

Compression – Pushing forces that crush and compact objects.
Shear – Offsets forces that deform shape by slippage along planes.
Torsion – Twisting forces that warp and twist objects.

Bending – Curving forces that fold or flex objects.

Signs of stress damage include:

Cracks, fractures, punctures from tension or shear forces.

Buckling, crushing, compacting from compressive forces.
Shaking, vibration that leads to fatigue fractures.
Permanent warping, twisting deformations.

Plastic deformation when yield strength is exceeded.

Careful design is required to ensure objects are operated within safe stress ranges. Regular inspection for early cracks or deformations is critical. Reinforcing structural points prone to stress can also mitigate damage.

Abrasive Damage

Friction from abrasive actions grinds away material over time. Some key factors leading to abrasion include:

Contact pressure – More force applied increases abrasion rates.
Motion – Faster speeds and more cycles increase wear.
Grit sizes – Roughness and hardness increases abrasiveness.

Material properties – Softer materials get damaged faster.
Temperature – Heat softens materials and increases abrasion.

Abrasion damage examples:

Pitting, gouging, erosions from particle impacts.
Reduced thickness and roughness from sliding contact.
Polishing, brightening, smoothing from rubbing.

Sanding, grinding, machining actions.
Fretting wear at press fitted joints that vibrate.

Methods to reduce abrasion damage include lubrication, coatings, material selection, machine isolation, and geometry changes to avoid contact and impacts.

Fatigue Damage

Fatigue damage occurs when cyclic stresses weaken points in an object until cracks initiate and propagate to failure. This process has three stages:

Crack initiation – Cyclic stresses start micro-cracks at weak spots in the material.
Crack growth – The micro-cracks slowly spread with each cycle.

Sudden fracture – The cracks reach critical length and the part fractures.

Factors leading to fatigue damage:

Tensile cyclic stresses from sources like vibration, loading, thermal expansion, etc.

Greater magnitudes, frequency, and duration of cycles accelerate damage.
Surface flaws like scratches or dents create stress concentrations.
Environmental factors like temperature and corrosion accelerate crack growth.

Key ways to prevent fatigue damage:

Reduce cyclic stresses by design changes, vibration damping, load control, etc.
Select materials resistant to fatigue like steel alloy.

Induction hardening and shot peening induces compressive stresses that resist micro-crack growth.
Ensure surfaces are smooth and free of defects during manufacturing.
Perform regular inspections for early crack detection and part replacement.

Corrosive Damage

Corrosion gradually degrades materials through chemical reactions like oxidation. It requires an electrolyte like water and depends on factors like:

Material composition – More readily oxidized metals corrode faster.
Exposure – Temperature, humidity, saltwater increase corrosion rates.

Stress levels – Tensile stresses accelerate crack growth.

Common types of corrosion damage:

Rusting – Iron oxidation causing weakness, staining, and expanded volume.

Pitting – localized holes and penetrations into metal.
Cracking – anode/cathode galvanic reactions breaks bonds.
Erosion corrosion – combined corrosion and abrasion in fluids.

Dealloying – One metal leaches out of an alloy.

Methods used to manage corrosion damage:

Material selection – Use less reactive noble metals like stainless steel.

Coatings – Paints, platings, and sealants provide a barrier.
Cathodic protection – Impressed current counters corrosion reactions.
Sacrificial anodes – Less noble metals corrode before the protected metal.

Cleaning and maintenance – Remove buildup and store properly.

Wear and Erosion

Wear is the gradual removal of material from surfaces through mechanical action and motion. It depends on factors like:

Contact pressure

Speed of relative motion
Surface roughness, hardness
Type of motion – rolling, sliding, impacting

Environment – lubrication, temperature, particles

Common examples of wear damage:

Scuffing – roughened glossy areas from friction.

Scratching – thin scraped lines from hard particle contact.
Pitting – small hollow spots from surface fatigue.
Abrasive wear – Loss of material from hard particles.

Adhesive wear – Micro-welding and material transfer between surfaces.

Wear damage control methods:

Material selection – Harder, tougher, and wear resistant materials.

Lubrication – Oils or greases separate surfaces and reduce friction.
Coatings – Surface treatments improve hardness and slickness.
Design changes – Modify contact pressures, geoemtry, motions, and tolerances.

Preventative Maintenance

Preventative maintenance is key for avoiding mechanical damage and extending system lifetimes. This includes:

Inspections – Periodic visual, physical, and non destructive tests to identify damage early.
Serving – Conduct lubrication, adjustment, cleaning and surface treatments.

Replacement – Swap out worn parts before failure.
Testing – Validate proper function, settings, and tolerances.

Maintenance planning balances frequency and effort against risk tolerance and budgets. Tracking failure causes also highlights weaknesses needing improvement.

Automated condition monitoring systems with vibration analysis, ultrasonic testing, fluid analysis, etc. also enable early identification of developing mechanical damage.

Design Considerations

Proper design is critical for avoiding mechanical damage from the start. This includes:

Materials – Select strong, ductile, and wear resistant materials.

Pressure – Keep stresses below strength limits.
Loads – Static and dynamic load analysis.
Factors of safety – Over-design parts relative to loads.

Geometry – Avoid thin sections and high stress points.
Clearance – Prevent jamming interference.
Lubrication – Enable smooth operation and wear reduction.

Analysis tools like finite element analysis simulate stresses and optimize the design. Lifetime testing also validates designs against target reliability metrics.

Manufacturing Defects

Defects and errors during manufacturing processes are another cause of mechanical damage:

Voids in castings from gas bubbles.

Cracks from overheated metal during heat treating.
Uncontrolled surface roughness from machining.
Overstressing parts during forming processes.

Out of spec fits, tolerances, or alignments.

Consistent quality control and process standards help minimize manufacturing defects. This includes measurements, statistical control, handling procedures, operator training, and more.

Operational Abuse

Improper use and overloading equipment beyond design limits results in mechanical damage. Issues include:

Exceeding speed, pressure, load, torque limits.
Improper tool use generates excessive impact forces.
Misalignment strains components.

Unauthorized modifications weaken structures.
Lack of lubrication or servicing causes wear.
Not following run-time or maintenance instructions.

Operator training, control systems, supervision, and policies help minimize equipment abuse during operations.

Environmental Exposure

Environmental conditions beyond those expected can lead to mechanical damage:

Temperature extremes – Expansion, weakened material strength.

Water ingress – Corrosion initiators in electronics, biological growth.
Chemical contamination – Reactions weakening materials.
Weathering – UV and moisture degradation of seals and coatings.

Dust/debris – Creates abrasive wear, clogs mechanisms.

Assessing operating environments and providing sufficient protection is necessary to avoid unanticipated damage factors.

Vibration Issues

Vibration causes many types of mechanical damage, including:

Loosening of joints, fasteners, and attachments.
Fretting wear as components micro-slide.
Fatigue cracks from cyclic stresses.

Misalignment from shifting components.
Noise that interferes with other equipment.

Balancing, alignment, damping, isolation mounts, and design for resonances prevents vibration outcomes.

Contamination

Contaminants in lubrication and operation environments cause multiple forms of mechanical damage:

Particulates create abrasive wear.
Chemical contamination degrades lubricant protecting surfaces.

Biological contamination corrodes and decomposes materials while impacting motion.
Water causes corrosion and interferes with lubricant properties.

Filtration, seals, maintenance procedures, and material selection control contamination risks.

Conclusion

In summary, mechanical damage arises from many sources that apply stress, friction, corrosion, and unwanted forces against equipment. Being aware of these degradation mechanisms is the first step toward preventing damage. Careful design, manufacturing controls, maintenance programs, operating procedures, and operator training are all needed to maximize service lifetimes and avoid equipment failures. New monitoring technologies and analysis techniques continue to improve early damage detection and prevention capabilities.