Internal Tensile Stress Research Articles

Interplay of Consolidation Fronts and Cracks in Drying Colloidal Coatings and Its Application in Controlling Crack Pattern Formation

Cracks are frequently observed in drying colloidal coatings. Although a rich collection of crack patterns has been reported, the systematic study on how cracks grow into the final morphology during the drying process remains elusive. In this work, we use directional drying channels with wedge-shaped edges of different angles to study the interplay of advancing consolidation fronts and propagating cracks. We found that although the shape of the advancing consolidation fronts is altered by the drying edge, the growth direction of the following cracks remains perpendicular to the consolidation fronts during the whole drying process, resulting in cracks with a large curvature. We rationalize the evolution of consolidation fronts with the distribution of capillary pressure revealed by a Laplace model. Further, the growth direction of cracks can be explained by the fracture mechanics mechanism that the main orientation of internal tensile stresses developed during the consolidation determines the crack growth direction. Utilizing this understanding, wavy crack patterns are generated in rectangular drying channels with an alternating temperature field, demonstrating a feasible method of designing and controlling drying-induced crack patterns for micro-/nano-fabrication applications.

Impact of polyvinyl alcohol fiber on the full life-cycle shrinkage of cementitious composite

Engineered cementitious composite (ECC) enjoys huge potential in building structures thanks to its excellent tensile performance and energy absorption ability. However, free deformation of ECC deserves better understanding since large shrinkage strain usually induces internal tensile stress which would lead to cracking under constraint. Present study focuses on the full life-cycle shrinkage of polyvinyl alcohol (PVA) fiber reinforced ECC. Shrinkage and relative humidity (RH) at three water to cement (w/c) ratios were experimentally tested through novel integrated deformation measurement device. In contrast, plain mortars with the same w/c ratios were compared to evaluate the impact of PVA fiber on the over-time deformation and RH characteristics. Thereafter, shrinkage model considering fiber influence coefficient is established to simulate autogenous and drying shrinkage of PVA-ECC. Results show that full life-cycle shrinkage can be divided into two stages according to the internal RH measured. Distinct restraint effect of PVA fiber on both stages are observed. By comparing experimental and simulation results of PVA-ECC, the proposed fiber influence coefficient-based shrinkage model well illustrates the effect of PVA fiber, especially for high strength cementitious composites with relatively low w/c.

Structural performance of steel plates

In general, plates are classified as thick plates when the minimum dimension to thickness ratio (b/h) is less than 10, thin plates when the b/h ratio ranges from 10 to about 100, provided that the plate maximum deflection to thickness ratio (w/h) is less than 0.2, and membranes when the b/h ratio approaches 100 and w/h ≥ 0.2. Thick plates develop internal stress resultants governed by three-dimensional elasticity similar to that of a solid body. Thin plates behave as plane stress members governed by two-dimensional elasticity. Membranes can only develop internal tensile stress within the plate’s neutral plane. Few studies have adopted b/h ratios between 90 and 110 to investigate the feasibility of the utilization of such plates in their various available forms. The current study with the b/h ratio of 100 aims to fill the gap. Steel Plates are available in different forms such as intact plates, stiffened, perforated, and stiffened perforated plates. They are used in buildings, bridges, ships, as well as aerospace structures. In this study, the investigated steel plate has a square shape and is subjected to uniaxial loading. The plate edges are simply supported. The plate is 200 mm wide and 2 mm thick. In this case, the critical buckling strength is, in general, less than the plate maximum strength. With further loading, the plate would experience an undesirable sudden mode of failure owing to buckling instability. This study aims at investigating the performance of the different forms of square steel plates, such as intact, stiffened, perforated, and perforated stiffened, when the minimum dimension to thickness ratio is 100. A pushover finite element linear elastic buckling analysis as well as a nonlinear large deflection buckling analysis have been carried out. The study indicated that the increase in the plate maximum strength in single, double, and triple stiffener plates was 75.6%, 174%, and 196%, respectively, compared to that of the intact plate. Based on the obtained results, it is concluded that the utilization of plates having the b/h ratio of 100 is feasible provided that the appropriate plate form is adopted.

Quenching Stress of Hot-Rolled Seamless Steel Tubes under Different Cooling Intensities Based on Simulation

Large residual stress occurs during the quenching process of hot-rolled seamless steel tubes, which results in bending, cracking, and ellipticity exceeding standards and seriously affects the quality of hot-rolled seamless steel tubes. In addition, the stress generation mechanism of hot-rolled seamless steel tubes is different from that of steel plates due to the characteristics of annular section. In this research, the finite element simulation method was used to study the quenching residual stress of seamless steel tubes with different cooling intensities. The variation law of temperature and stress on the steel tube under different cooling intensities were analyzed. The results show that the radial stress was close to 0, and the circumferential and axial stresses were the main factors affecting the quality of the steel tube. With the increase in the cooling time, the magnitude and direction of each stress component of the steel tube changed simultaneously. Finally, a typical stress distribution state of “external compressive stress, internal tensile stress” was presented in the thickness direction of the steel tube. Furthermore, with the increase in the cooling intensity, the residual stress of the steel tube gradually increased and was mainly concentrated on the near wall of the steel tube.

Quantitative consideration in selection of breakwater concrete armor unit based on unit’s internal tensile stress response

Concrete armor units are essential for the protection of rubble mound breakwaters, yet their selection is generally not based on structural integrity considerations. In this study, the authors used static finite element simulations, as implemented by Ansys software, to compare the structural integrity of five armor units: Accropode, A-Jack, BPPT-Lock, tetrapod, and dolos. All armor units have a mass of around 11,500 kg and have the same quality of concrete at f’c of 30 MPa. The study involves two different loading cases: Armor units were (1) arranged on a breakwater slope subjected to their own weight and (2) placed on a horizontal ground subjected to idealized wave attacks. In Case #1, the armor units were modelled fixed to the ground and bonded to each other. In Case #2, the wave attack was modelled as a unidirectional and uniform pressure. From the simulation results, the authors compare the highest tensile stresses which could be found on the corner regions of the armor units—their most vulnerable region. In both cases, armor units with stocky shapes experience lower tensile stresses compared to those with slender shapes. These results confirm that Accropode, BPPT-Lock, and tetrapod are structurally safer than dolos and A-Jack.

Thermal Properties of Hydrated Lime-Modified Asphalt Concrete and Modelling Evaluation for Their Effect on the Constructed Pavements in Service

Flexible pavements are subjected to three main distress types: fatigue crack, thermal crack, and permanent deformation. Under severe climate conditions, thermal cracking particularly contributes largely to a considerable scale of premature deterioration of pavement infrastructure worldwide. This challenge is especially relevant for Europe, as weather conditions vary significantly throughout the year. Hydrated lime (HL) has been recognized as an effective additive to improve the mechanical properties of asphalt concrete for pavement applications. Previous research has found that a replacement of conventional limestone dust filler using hydrated lime at 2.5% of the total weight of aggregates generated an optimum improvement in the mechanical properties of the asphalt concrete mixes used for all three purposed layers (i.e., wearing, levelling, and base) at atmospheric temperatures from mild to relatively high. This paper reports on a continuous experimental test for the thermal properties of the optimized hydrated lime-modified mixes. The experiment together with that conducted before provides the required data to characterize the thermomechanical constitutive relations of the optimized hydrated lime-modified mixes. The obtained thermal and mechanical properties thereafter were implemented in a numerical modelling study for a scenario involving pavement exposed to coupled thermal and traffic service conditions. The study has demonstrated that using HL in mineral filler enhances the thermal properties of asphalt concrete, which, however, showed little influence on the local temperature profiles within the pavement structure. The thermal effect is pronounced under the coupled thermomechanical conditions for a pavement exposed to both traffic and climatic impacts. The HL pavement has about 1.5% less deformation, and 39% less stress level under traffic loading only, but the thermal effect increases the maximum total internal tensile stress level by 26% in the HL pavement in winter season. The modelling analysis has shown that the local maximum tensile stress dominates in the surface region of the HL pavement. It will help to reduce the workload of crack repairing and in long term help on saving costs and efforts of maintenance.

Prevention of concrete breakout failure of expansion anchor in tension by post-installed reinforcement: Discrete analysis and experiment

Concrete breakout failures with acutely damaged concrete are one of the main problems caused by expansion anchors under tensile loading. In this study, the prevention of concrete breakout is investigated by post-installed reinforcement (PRs). Experimental and numerical studies were conducted to look into the effect of the PRs on the expansion anchors subjected to tensile loads. The 3D Rigid Body Spring Model (RBSM), which is based on discrete analysis at the mesoscale, was used as supporting numerical research. On pullout capacity, displacement, failure mechanism, and concrete breakout geometry, both experimental and numerical analyses were undertaken. The numerical analysis also looked at internal stress, strain, and concrete cracking. In general, the anchors with the PRs had steady displacement (ductile) and less brittle failure compared to the anchors without the PRs. The significant finding was in the failure mode, where severe concrete damage and concrete breakout failures were prevented by the PRs. The internal tensile stress of concrete was concentrated around the wedges of the anchors (interlocked area). The contribution of the PRs was shown by high strain values at around their mid-length. Additionally, due to the PRs, concrete cracking was less, mostly generated in the region between an anchor and its PRs. The utilization of PRs could be a method to protect concrete from breakout failure.

Hot cracking evolution and formation mechanism in 2195 Al-Li alloy printed by laser powder bed fusion

Al-Li alloys printed by laser powder bed fusion (LPBF) have huge potential for industrial application due to their remarkable advantages. However, the high hot cracking susceptibility (HCS) due to the addition of Li is still a key restraining factor for their rapid development towards such industrial application. Here in this report, hot cracking behaviour of 2195 Al-Li alloys fabricated by LPBF process was investigated by a three-dimensional (3D) X-ray micro-tomography technique. The relationship between the microstructural evolution and the high HCS was established to reveal the hot cracking mechanism for the first time. Observations by X-ray tomography showed large, interconnected cracks with a 3D reticular structure in the printed samples, extending layer by layer from the lamellar cracks in the previous single tracks along the building direction. Contributions to hot cracking were found to origin from the stable liquid film and the stress concentration. The segregation between the Al6CuLi3 and α-Al matrix contributed to the Al-Cu eutectics along the high-angle grain boundaries in form of intergranular liquid films. Furthermore, it was found that the interfacial layer (intradendritic liquid film) between the Al2Cu and the adjacent LiAlSi or AlCuMgAg exhibited the reduced micro-crack resistance in the interior of the grains. It was pointed out on the basis of the calculation that the higher stability of the intergranular liquid film led to a higher HCS at the grain boundaries as compared to that in the interior of the grains. Furthermore, high internal residual tensile stress provided the driving force for the crack initiation and propagation. In summary, this work contains a practical guide to optimize the powder composition and processing steps of high-quality Al-Li alloys produced by LPBF.

Effect of laser irradiation on high-temperature crystallization behavior, oxidation resistance, and corrosion performance evaluation of electrodeposited amorphous Ni-P coatings

Amorphous Ni-P alloys crystallize at high temperatures, which leads to the deterioration of resistivity and corrosion resistance. In this study, the use of laser irradiation with the electrodeposition (ECD) process for preparing amorphous Ni-P coatings was investigated; and the resistivity and corrosion resistance were analyzed, which is related to crystallization process, surface morphology, residual internal stress, and oxidation layer. The results indicates that the crystallization rate of Ni-P coating prepared by laser-assisted electrodeposition (LECD) was slower than that of ECD coating. With increasing ambient temperature, the internal tensile stress first decreased and then increased. The LECD coating has better oxidation resistance, with XPS indicating the oxide layer mainly comprised Ni-O compounds. At the same ambient temperature, the resistivity of the LECD coating was higher than that of the ECD coating. The Ni-P coating had better corrosion resistance after heating, and the corrosion mechanism changes from stress corrosion to pitting corrosion.

Fracture Toughness of Free-Standing ZrSix Thin Films Measured Using Crack-on-a-Chip Method

In this work, we experimentally measure fracture toughness of free-standing zirconium ZrSiₓ thin films using the crack-on-a-chip method. In this method, fracture toughness is determined from the analysis of cracks, which propagate and arrest in specially designed free-standing test structures. The test structures use a well-known double cantilever beam geometry, which enables crack arrest, and don't require any external force actuation, but instead rely on the internal tensile stress of the tested thin film. To produce the ZrSiₓ test structures, a universal fabrication process was developed and used, which avoids typical issues related to etch selectivity and that can be readily applied for other thin film materials. Unlike in previous studies, which used the crack-on-a-chip method, in this work crack initiation was triggered only after the test structures were fully fabricated, which allowed to avoid the influence of the fabrication process on the extracted toughness values. For this, blunt pre-cracks included in the structures were ``sharpened'' using focused ion beam, which resulted in rapid crack propagation and subsequent crack arrest. Mechanical analysis done by a finite element method to extract the values of fracture toughness, showed that buckling of the free-standing thin film test structures has a strong influence on the results of fracture toughness calculations and therefore cannot be ignored. The fracture toughness of ZrSiₓ thin films was determined to be 2.1±0.13 MPa*m <formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex> $^{0.5}$ </tex> </formula> .

Analytical prediction of tensile stress of photomask protective membranes based on measured frequency spectrum

The quality of photomask protective membranes is generally quantified in terms of its internal tensile stress. However, the tensile stress is not easily measured directly using experimental methods. Hence, the present research derives an theoretical model based on large deflection assumption for predicting the frequency spectrum of a pellicle. Using this model, the tensile stress of any membrane can be inversely derived by comparing the predicted frequency spectrum obtained using different tensile stress estimates with that determined experimentally using confocal microscopy and fast Fourier transform. The feasibility of the proposed approach is demonstrated by comparing the calculated frequencies of the main vibration modes of three commercial pellicles with the experimental results. The validated model is then used to investigate the effects of the membrane initial displacement, membrane width, and membrane thickness on the frequency response of a typical pellicle membrane.

Study on Temperature Control and Crack Prevention Scheme for Lining Concrete Construction of Spillway Tunnel in Summer

In view of the characteristics of high strength and thin thickness of spillway tunnel lining concrete, the temperature field and stress field of spillway tunnel lining concrete during summer construction are simulated by using large-scale finite element software SAPTIS, and the risk assessment of lining concrete surface flow maintenance time and internal water passage time on its own cracking during summer construction is analyzed. For a project, the simulation calculation is carried out, and the results show that under the given working conditions, compared with non-flow curing, the surface point stress of surface flow curing for 28 d decreases by 1.34 MPa, and the minimum crack safety factor increases by 0.79 ; the internal middle point stress decreases by 0.75 MPa, and the safety factor increases by 0.31. The cooling time of internal water in lining concrete is longer than the time when the maximum temperature of concrete occurs, which cannot effectively reduce the maximum temperature of internal temperature, but it can reduce the internal tensile stress to a small extent and improve the safety factor. The research results have guiding value for thermal control and crack prevention of lining concrete.

Structural parameters and critical anchorage length of tunnel system bolts made of basalt fibre

Basalt fibre reinforced polymer (BFRP) has the advantages of high tensile strength and good durability; therefore, the anchor bolt developed with BFRP has potential application in tunnel surrounding rock anchorage. This study used meso-scale numerical simulation and laboratory tests to examine the structural parameters of BFRP anchor plate and rod and the critical anchorage length of BFRP cement mortar anchor. The results showed that: 1) the special-shaped truncated cone type anchor plate can convert the axial force into internal tensile stress, which improves the tensile performance of the basalt fibre material. 2) The larger the thread pitch of the BFRP bolt or the smaller the thread height, the more uniform is the shear stress distribution of the bolt thread, and the smaller is the maximum shear stress of the rod and nut. 3) The thread height of 2 mm and thread pitch of 18 mm is the optimal combination. 4) The critical anchoring length of the BFRP cement mortar bolt is 20–40 times its diameter. The findings of this study can provide new and meaningful reference for the application of System Bolts made of Basalt Fiber in tunnel engineering.

Numerical study of deformation behavior of rolled AZ31B plate under cyclic loading in different material orientations based on the EVPSC-TDT model

The EVPSC-TDT model is employed to mimic the stabilized stress-strain hysteresis loops of the rolled AZ31B plate under cyclic loading in different material orientations. The predicted stabilized stress-strain hysteresis loops for different material orientations are generally in good agreement with the corresponding experimental data. The key features associated with twinning and detwinning are interpreted in terms of activities of deformation modes. To appropriately mimic the cyclic plastic response of the rolled AZ31B plate, cyclic loading experiments should also be accounted for in determining the Voce-type hardening law parameters in the current model. The equation proposed in the literature is used in the current model to describe the evolution of residual twinning during cyclic loading, and a threshold equation with a new parameter is proposed to constrain fresh twinning and retwining. The effects of parameters in the two equations on cyclic plastic response are investigated. To approximately describe the apparent easier reverse motion of twin boundaries, the initial CRSS of detwinning is set to be half of that of twinning, and for simplicity the other voce-type hardening law parameters are kept the same for both twinning and detwinning. The effect of initial CRSS of detwinning on plastic response during reverse loading is also investigated. The inelastic behavior is predicted to occur at the very end of the unloading process for the 90° (ND) material orientation, which is ascribed to detwinning. It is assumed that the magnitude of internal tensile stress upon unloading together with that of the activation stress for detwinning determine when or whether detwinning will occur during unloading. The discrepancies between numerical simulations and experiments of the pseudo-elasticity behavior might be because the current mean field model based on self-consistent schemes might not properly describe some microstructure related properties of the AZ31B plate and so underestimates the internal tensile stresses of twinned grains before unloading, which deserves further investigation.

Stress corrosion behavior of friction stir welding joint of 7N01 aluminum alloy

The friction stir welding joint of 7N01 aluminum alloy has strong stress corrosion sensitivity due to the inhomogeneity of microstructure. In this paper, the stress corrosion behavior of 14 mm thick plate 7N01-T4 welding joint and base metal was investigated by means of electrochemical impedance spectroscopy, slow strain rate tensile test and electron back scattered diffraction. The results show that the charge transfer resistance of the welding joint is obviously lower than that of the base metal. The lowest impedance at the joint is 698 Ωcm2, but the lowest impedance is 1082 Ωcm2 at the base metal.The lowest Rct value at the weld is only 64.5% of the base metal. The thermal-mechanical affected zone on the rear side is the worst area of the resistance to stress corrosion. There are more deformed grains and larger Schmidt factor close to 0.5 in this area, and the different grain orientation can easily lead to the concentration of internal tensile stress and the formation of crack propagation.

Origin of the inverse elastocaloric effect in a Ni-rich Ti-Ni shape memory alloy induced by oriented nanoprecipitates

In the region of a martensitic transformation, conventional elastocaloric effect causes cooling when the forward parent to martensite transition is induced by loading under adiabatic conditions and by heating when the load is removed and the reverse transition occurs. An inverse elastocaloric effect might be expected if the reverse transition could be induced upon loading. However, this behavior is quite uncommon and inverse elastocaloric effect rarely occurs. Herein, we have successfully manufactured a Ti-50.8 at.% Ni crystal in a high proportion of favorable $R$ phase (martensite) variant containing single-variant ${\mathrm{Ti}}_{3}{\mathrm{Ni}}_{4}$ nanoprecipitates aligned along the ${\ensuremath{\langle}111\ensuremath{\rangle}}_{B2}$ direction of the $B2$ parent phase, by means of a compressive stress associated aging along the ${\ensuremath{\langle}111\ensuremath{\rangle}}_{B2}$ direction. The material displays inverse elastocaloric effect induced by compressive stress along the ${[111]}_{B2}$ direction in the temperature range of stability of the $R$ phase. This inverse elastocaloric effect is caused by the stress-induced reverse transformation of the high proportion of favorable $R$-phase variant that occurs when the external compressive stress is applied along the direction of the internal tensile stress induced by the aligned ${\mathrm{Ti}}_{3}{\mathrm{Ni}}_{4}$ nanoprecipitates. The mechanism giving rise to this inverse elastocaloric effect is explained by the transformation strain in the ${[111]}_{B2}$ and ${[1\overline{1}0]}_{B2}$ directions for different $R$-phase variants based on crystallography. Results indicate that the stress-associated aging process is an effective way of patterning materials to display inverse elastocaloric effect through controlling the alignment of the ${\mathrm{Ti}}_{3}{\mathrm{Ni}}_{4}$ nanoprecipitate in the Ni-rich Ti-Ni shape memory alloy.

Effect of electrodeposition parameters on the evolution of crystallographic texture and internal stress of Ni/ZrC composite coatings

Crystallographic texture and internal stress are two important aspects of microstructures, responsible for various physical and chemical properties of electrodeposited composite coatings. This paper aims to understand how preparation parameters such as current density, size and concentration of second-phase particles, particularly deposition time, influence the crystallographic texture and internal stress of electrodeposited Ni matrix composites. The results show that the evolution of surface morphology, crystallographic texture and the internal stress of electrodeposited Ni/ZrC composites is strongly related to the content of incorporated ZrC in coatings, which increases after an increase in the amount of ZrC particles loaded in the electrolyte, from 0 g/L to 40 g/L, and from a decrease in applied current density, from 20 A/dm2 to 1.25 A/dm2. By increasing the ZrC content in coatings, the crystallographic texture of Ni/ZrC is depressed and internal stress is modified from 329.48 MPa to 56.71 MPa. During electrodeposition, the exhibited texture changes from <111> initial texture to <100> growth texture for pure Ni coatings, and to random orientation for Ni/ZrC coatings. The tensile internal stress of Ni/ZrC decreases, followed by a gradual increasing with an increase of thickness. ZrC nanoparticles incorporation results in Ni/ZrC coatings with a weaker texture and lower internal stress than Ni/ZrC coatings that incorporate ZrC micron particles.

A comparative study on the mechanical properties, autogenous shrinkage and cracking proneness of alkali-activated concrete and ordinary Portland cement concrete

This study aims to compare the developments of mechanical properties and autogenous shrinkage related properties of alkali-activated materials-based concrete (AC) and ordinary Portland cement-based concrete (OC) against curing age and degree of reaction. Temperature Stress Testing Machines are utilized to monitor the evolution of the internal tensile stress and the cracking occurrence in the restrained concrete. It is found that AC shows lower tensile strength-to-compressive strength ratios than OC. The mechanical properties of both OC and AC can be modelled by a power law against the degree of reaction. AC shows higher autogenous shrinkage, but later cracking than OC when under restrained condition. However, the degrees of reaction at which AC and OC cracked are very similar. From the autogenous shrinkage, the elastic modulus and the self-induced stress, the elastic and creep deformations of the concrete can be calculated. AC is found to show much higher creep coefficient than OC.

Numerical investigation of the tensile strength of loess using discrete element method

The tensile strength of loess is important for the tension-related crack and failure in the Loess regions. While the previous work on the tensile strength of loess mainly focuses on the test method and its variation with different internal and external factors, the micro-mechanical characteristics of the tensile experiments are seldom studied. Taking the unconfined penetrated test (UP test) as example, the tensile strengths and internal stress distributions of undisturbed loess samples under the loading plate-sample ratios (d/D) ranging from 0.05 to 0.95 are numerically investigated using discrete element method. The internal stress distribution, failure pattern of sample and variation of internal crack are clearly reflected by the discrete element modelling. The DEM simulation results also show that: 1) the d/D in the range of 0.15 to 0.35 is recommended for measuring the tensile strength of undisturbed loess; 2) the tensile strength of undisturbed loess increases with d/D recommended above ;3) the failure of sample is mainly controlled by the tensile stress when the d/D is equal or lower than a critical d/D 0.50, while that is mainly controlled by the compressive stress when the d/D is larger than a critical d/D 0.50. This study shows the capability of discrete element method to simulate the UP test, thereby providing us a relatively reliable way to investigate the tensile strength of loess numerically and to explore the internal stress and crack distribution of soil sample.

Microstructural analysis of selective laser melted Ti6Al4V modified by laser peening and shot peening for enhanced fatigue characteristics

The increased availability of additively manufactured materials provides a new extended design freedom for innovative products and applications, especially with view to high-tech demands as in the aerospace industry. Current microstructural challenges relevant for fatigue life like internal processing defects and tensile macro stresses still require innovative post processing methods, where laser peening shows some potential, but with need of more understanding of materials modification and fatigue outcome. This study aims at giving for the first time a thorough microstructural insight of selective laser melted Ti6Al4V, modified by both, laser peening and conventional shot peening. The results for the laser peened state highlight an outstanding depth of residual macro and micro stresses (~2.3 mm zero level-crossing), whereas deformation characteristics are accompanied by a low level however characteristic dislocation structure preferably close to the lath grain boundaries, as well as an orientation dependent grain deformation at the surface. Differences compared to shot peening become clearly obvious, whereas initial roughness is shown to play a substantial role along with both post process effects. Fatigue results prove the usefulness of both processes with significant benefits for laser peening by a minimum of a factor of 10 number of cycles.