Shot peening and laser peening are proven surface enhancement methods that push fatigue life far beyond what base materials achieve. By creating deep, stable compressive stresses, they slow crack initiation and arrest growth in mission critical parts. This guide explains mechanisms, controls, and applications used across airframes, engines, and landing systems. Our list titled Top 10 Aerospace Shot Peening and Laser Peening Treatments for Fatigue Life balances fundamentals with advanced practice so readers at every level can learn how to specify, validate, and sustain robust processes. Follow the sequence to connect material behavior, process parameters, and inspection, and translate surface integrity into measurable durability gains.
#1 Surface integrity fundamentals
Shot peening plastically deforms the surface using controlled media impacts to induce compressive residual stress, which counters tensile loads that drive fatigue cracks. Depth, magnitude, and stability of stress depend on material strength, hardness, and temperature. Laser peening uses high energy pulses under a water overlay to generate stronger shock waves and deeper compressive layers without significant cold work. Both techniques also refine near surface grains and close micro notches. For aerospace hardware, this combination delays crack initiation at fillets, holes, and blended repairs, raising safe life and inspection intervals under demanding load spectra.
#2 Intensity and coverage control
Almen intensity quantifies energy imparted by measuring strip arc height after peening, while coverage describes the percentage of surface impacted. Proper saturation ensures consistent plastic strain without overpeening that can raise roughness or distort thin walls. Engineers establish saturation curves, then lock machine settings such as air pressure, wheel speed, stand off, and exposure time. For laser peening, pulse energy, spot size, overlap, and layers replace traditional parameters. High fatigue benefit requires at least full coverage with slight overlap, verified by replicas or fluorescent tracer methods, with rework defined when local coverage falls below target values.
#3 Media selection and conditioning
Media type and size shape the stress profile and surface roughness. Cast steel and cut wire are common for high strength steels, offering durability and tight size control. Glass or ceramic beads suit aluminum and titanium when lower roughness is required and cold work must be limited. Angular media can raise cold work and risk surface damage, while conditioned spherical media produce uniform dimples and stable intensity. Continuous classification, shot flow monitoring, and contamination control maintain consistency. Media life, breakage rate, and hardness must match the specification to avoid embedded debris and to preserve predictable intensity across complex geometries.
#4 Fixturing, masking, and robotics
Consistent impact angles and distances are essential on blades, disks, and landing gear. Dedicated fixtures orient features, while elastomer or metal masks shield critical bores, threads, and gauge surfaces that cannot be peened. Robotic manipulators execute tool paths with repeatable velocity and overlap, reducing operator variability and improving coverage in shadows. Digital twins of part and nozzle help validate reach, line of sight, and shadowing. Process sheets define path sequencing to avoid overexposure where passes intersect. For laser peening, precise water flow, sacrificial coatings where used, and beam delivery optics are integrated into rigid, vibration controlled setups.
#5 Residual stress verification
X ray diffraction directly measures near surface residual stress and can map depth using layer removal for profiles. Hole drilling with strain gauges offers another option for thicker sections when access allows. Incremental electropolishing exposes subsurface layers without adding mechanical damage that could bias readings. Engineers compare results to minimum compressive stress and depth criteria, sometimes correlated to fatigue life models. For laser peened parts, deeper compressive zones extend several millimeters, so measurement plans include deeper mapping at critical features. Routine audits trend stress data against Almen intensity, coverage, and media health to catch drift before it degrades durability outcomes.
#6 Surface finish and geometry control
While compressive stress improves fatigue, excessive roughness can reduce flow efficiency and act as stress concentrators. Post peen finishing such as controlled polishing, superfinishing, or isotropic finishing can restore low roughness without stripping compressive layers if parameters are tuned. Designers set limits for roughness, edge radii, and dimensional change to preserve aerodynamic and seal performance. Gauging ensures holes, slots, and airfoils remain within tolerance after peening and finishing. For laser peening, minimal roughness change is typical, yet optics induced patterning must be checked. Balancing texture, residual stress, and tribological requirements is central to reliable, high performance components.
#7 Engine rotating hardware
Fan and compressor blades face foreign object damage and high cycle fatigue at edges and root attachments. Shot peening strengthens leading edges, dovetails, and platform fillets, while laser peening targets deeper subsurface regions with high vibratory stresses. Disks benefit at bore and rim transitions where gradients are steep and defects can grow quickly. Peening pairs with blended damage removal to restore life within dimensional limits. Qualification uses strain gauge telemetry, spin pit tests, and coupon fatigue to prove margin under representative spectra. Improved resistance to crack initiation enables longer inspection intervals and lower scrap while meeting containment and burst safety requirements.
#8 Landing gear and structural fittings
High strength steels in axles, bogies, and trunnions are susceptible to corrosion fatigue and fretting at interfaces. Shot peening lifts stress intensity thresholds at fillets and bolt holes, improving safe life under spectrum loading from taxi, landing, and braking. Laser peening is applied where compressive layers are needed at thick sections or severe geometries that concentrate stress. Tight control of masking protects bearing bores and seal lands that cannot be roughened. Protective coatings must be applied after peening to preserve corrosion resistance. Fleet experience shows fewer crack indications and extended overhaul intervals when process control and inspection are maintained.
#9 Additive manufacturing and repairs
Additively built or repaired components can exhibit tensile residual stress and surface defects from layer wise fusion. Shot peening reduces as built tension, mitigates notch sensitivity, and homogenizes the surface after machining or blending. Laser peening adds deeper compressive fields that tolerate thermal gradients from subsequent processing and operational heating. Parameter windows are tuned to avoid collapsing thin lattice features while still achieving coverage and intensity. Qualification includes fatigue testing of representative coupons and computed tomography to assess defects. Integrating peening with heat treatment, HIP, and finishing yields consistent, certifiable durability for lightweight or repaired flight hardware.
#10 Specifications, qualification, and digital control
Aerospace programs rely on specifications such as AMS 2430, AMS 2432, and customer standards to define media, intensity, coverage, and inspection for each part family. NADCAP audits check procedures, training, and records against those requirements. Qualification blends coupon fatigue, residual stress evidence, and full part demonstration under load. Modern cells use closed loop shot flow control, machine vision coverage assessment, and data logging tied to serial numbers for traceability. For laser peening, validated beam parameters and path planning software ensure repeatability across shifts. A disciplined quality system links requirements to data so compressive stress, not variability, dominates fatigue outcomes.