A kind ofly optimize the method that two-sided laser impacts alloy thickness simultaneously
Technical field
The present invention relates to the reiforcing laser impact technology field, refer in particular to a kind ofly when utilizing two-sided laser to impact alloy simultaneously, improve the method for alloy strengthening effect.
Technical background
Laser impact intensified is to utilize power density greater than 10
9W/cm
2The laser beam impinge metal material surface of short pulse ns level produces high-intensity shockwave, peak pressure reaches the GPa level and propagates to metal inside, when forming intensive, stable misconstruction, make surfacing generation viscous deformation to produce very big residual compressive stress, thereby improve the mechanical property of metallic substance, as the surface strengthening technology of strength property, fatigue property etc.Laser peening is widely used because of characteristics such as the zero pollution of its uniqueness, high-level efficiency, high precision.
Domestic and international research to laser impact intensified alloy at present mainly concentrates on the situation that the target single face is dashed, and it is actual in actual life, especially on the component of some military aircrafts and aviation airship, blade as engine, pump leaf of water screw etc., because they expose in the external world, the tow sides of component tend to be subjected to simultaneously the test of various bad working environments, and usually need to bear the work of high strength, high capacity, take exercise and various wearing and tearing, corrosion etc. for fear of fatigue.This has proposed urgent requirement to how improving the two-sided mechanical property of target simultaneously.But when utilizing two-sided laser to impact the thin target material simultaneously, its optimal thickness is not simply to double the measured unrelieved stress depth value of experiment.Liquidate when bumping when two pulse shocks of front-back two-sided impact form, complicated relative movement and variation can take place in the residual stress field of alloy inside, thereby weaken the surface compress residual stresses layer, and the thickness of target is more thin, and this influence is more obvious.
When two-sided laser impacted alloy material simultaneously, alloy thickness was the important factor that influences its shock peening effect, still lacked the preferred method that two-sided laser impacts alloy thickness simultaneously at present.
Summary of the invention
The invention provides the two-sided laser of a kind of alloy and impact the thickness optimization method simultaneously, preferably provide the technical director for what two-sided laser impacted alloy thickness simultaneously, improve the two-sided mechanical property of target.
For solving above technical problem, the present invention adopts large-scale finite element analysis software, the alloy target material of simulating various different thickness is subjected to the distribution that two-sided laser impacts the residual stress field of positive and negative two surfaces, back and inside thereof simultaneously, the analog result that it and single face under the same laser impact condition are impacted compares, and the alloy target material of must sening as an envoy to obtains the optimal thickness of the unrelieved stress of the reinforcement degree of depth close with single-impact and identical numerical value magnitude when being subjected to two-sided impact.The concrete technical scheme that adopts is as follows:
Step 1 makes up a 2D axisymmetric model, and the simulated laser single face impacts alloy gained residual stress field, obtains the unrelieved stress curve of depth direction vertically;
Step 2, observing its maximum residual stress value and unrelieved stress influences the degree of depth, influences the degree of depth with the theoretical unrelieved stress of 2D axisymmetric model and compares, and calculates the matching degree between simulation and the theory, the reliability of checking analogy method;
Step 3 makes up the 2D axisymmetric model that many group thickness slightly superpose successively, in order to reduce the influence that edge reflection brings, will make that the model radius should be enough big, makes edge reflection be tending towards 0, so the radius of model should be more than or equal to 5 times of model thickness.Utilize described single face to impact identical laser technical parameters the process that two-sided laser impacts target simultaneously simulated, analog parameter is set:
(1) material property module input target mass density ρ kg/m is set
3, elastic modulus E MPa, Poisson's ratio υ, dynamically yield strength
MPa; It is non-independent community that entity type is set in load module;
(2) analysis step is set and in initial analysis step back Step-1 is set, the analysis step type is made as the demonstration dynamic class, open geometrical non-linearity, analyze duration and be made as 4000 ns, when utilizing explicit module analysis dynamic stress state, for calculating can be restrained, so time increment should be less than the stability limit of alloy;
(3) according to the difference of model thickness, select different mesh-densities; Cell type is made as demonstration, and grid stand under load type is made as axi symmetrical stress..
(4) according to the pulse width of testing set laser, the pressure pulse time length is traditionally arranged to be 2 ~ 3 times of laser pulse width, add the symmetrical final condition of U1=UR2=UR3=0 at its symmetry axis place, right side, apply the pulsating pressure with the identical size of single-impact same radius at the close symmetry axis place of last bottom surface; Submit to initial Job to analyze at last;
(5) simulated data with (4) calculating gained imports to new model block, the predefine field that load in the new model is set is former Job title, delete original Step-1, a newly-built Step, type is set to static implicit expression, the type of revising grid cell at mesh module is implicit expression, submits to new Job to carry out the resilience analysis at last, obtains stable residual stress field:
(6) the many group models of the comparative analysis unrelieved stress curve of depth direction vertically, choosing the unrelieved stress of impacting gained with single face influences the degree of depth and differs model at ± 0.1mm, finds out the least model thickness that unrelieved stress maximum value wherein reaches capacity and is optimal thickness.
Step 4, the model of the different thickness unrelieved stress curve of depth direction vertically in the comparative analysis step 3, with the model thickness that satisfies following 3 requirements simultaneously as optimal thickness:
The unrelieved stress maximum value reaches capacity;
The unrelieved stress that single face impacts gained influences the degree of depth and differs at ± 0.1mm;
Satisfy the least model thickness of above 2 conditions.
Implementing beneficial effect of the present invention is: by the finite element simulation simulation, can obtain the optimization model thickness that two-sided laser impacts alloy simultaneously, make two-sided laser while shock peening effect reach best, thereby improve the two-sided mechanical property of target.
Description of drawings
Fig. 1 optimizes two-sided laser to impact the synoptic diagram of alloy thickness approach simultaneously.
Fig. 2 is the single-impact target residual stress distribution figure of depth direction vertically.
Fig. 3 is that two-sided laser impacts different thickness target residual stress distribution figure vertically simultaneously.
Embodiment
Below in conjunction with accompanying drawing the specific embodiment of the present invention is elaborated:
The target material that the present invention simulates is the AM50 magnesium alloy, density p=1800 kg/m
3, elastic modulus E=44800 MPa, Poisson's ratio υ=0.3, dynamically yield strength
=375 MPa, pressure pulse width are t=57 ns.The peak pressure that laser produces is made as 1600 MPa.
The stress waves in soils that laser-impact produces is in target internal communication process, the strongest at the stress waves in soils that just contacts plate surface, strengthening effect to sheet material is best, along with the increase of stress waves in soils to target internal communication distance, intensity declines gradually, strengthening effect to material is also weakening gradually, until producing reverse residual tension.
Theoretical unrelieved stress under the laser-impact effect influences the degree of depth
Can estimate by following formula:
In the formula
,
Be respectively elastic wave and the plastic wave velocity of propagation in sheet material, magnesium alloy
=5.74 * 10-
6Mm/s,
=4.44 * 10-
6Mm/s,
Be that shockwave action time is 57 ns,
=656 MPa.Will
,
,
,
,
Substitution (1) formula, obtaining theoretical unrelieved stress influences the degree of depth
≈ 0.84 mm.
At its depth direction, the simulation gained along the residual stress distribution of central shaft as shown in Figure 2, in its axial depth direction, maximum residual stress is up to-250 MPa, unrelieved stress influences the degree of depth and is about 0.88 mm, influence the degree of depth with the theoretical unrelieved stress of calculating gained and well coincide, matching degree is up to 95.45%.By above analysis as can be known, by utilizing the accurate simulated laser of 2D axisymmetric model to impact the residual stress field that target produces.
As shown in Figure 3, be the five group models distribution plans of depth direction unrelieved stress vertically, model A1, A2, A3, A4, A5 thickness is respectively 1mm, 2mm, 3mm, 4mm, 5mm, the radius unification is made as R., and we can find out very clearly from figure, model A1 and A2 curve fluctuation are all very big, but both compare, can clearly see, the unrelieved stress average of model A2 will be much larger than A1, the residual compressive stress maximum value of A1 is about-30 MPa, and A2 is about about-100 MPa, model A3, A4, the A5 residual stress distribution is similar, the residual compressive stress maximum value all is about-200 MPa, i.e. A3, A4/A5 residual compressive stress maximum value has reached saturated.
It is to judge a very important measurement index of laser impact intensified effect that residual compressive stress influences the degree of depth, want to make the effect after the two-sided impact of target to reach best, the degree of depth that influences that namely will make the surface residual stress of two-sided impact target influence the degree of depth and single-impact is consistent as far as possible.After the A3 model impacts simultaneously through two-sided laser as shown in Figure 3, it is about 0.6 mm that unrelieved stress influences the degree of depth, A4 influence the degree of depth be about 0.87 mm greater than A4 influence the degree of depth 0.85 mm, the unrelieved stress of model A4 and A5 influences the degree of depth all near 0.88 mm of single-impact.Both differ 0.03 mm and 0.01mm respectively, less than 0.1 mm.We draw the AM50 magnesium alloy to carry out the optimal thickness that two-sided laser impacts simultaneously are 4 mm by above analysis.