| Glass fiber,basalt fiber and carbon fiber are typical mineral fibers of reinforced resin matrix composites.They have excellent comprehensive properties and are widely used in aerospace,automotive,chemical industry,mechanical manufacturing and medical fields.Due to the inertia on the surface of mineral fibers,the poor wettability and low bonding strength between mineral fibers and resin matrix limit the overall performance of the composites.Therefore,it is of great theoretical and practical significance to modify glass fiber,basalt fiber and carbon fiber to improve their surface properties and broaden their application range.In this paper,glass fiber,basalt fiber and carbon fiber were modified by high energy laser beam,and fiber/epoxy resin composites were prepared.SEM,AFM,XRD,EDS and XPS were used to characterize the morphology,mechanical properties,phase structure,chemical composition,wettability of three kinds of mineral fibers before and after modification and mechanical properties of modicated fiber/epoxy resin composites.The effects of laser irradiation on the micro structure and properties of the fiber were systematically studied.The mechanism of laser to mineral fiber and modification was explored.The experimental results showed that,for laser surface modification,physical modification was the main aspect.In the aspect of "primary structure",the surface defects of glass fiber,basalt fiber and carbon fiber were changed by laser surface modification.With the increase of modification power,the depth and area of surface defects of glass fiber and basalt fiber increased,and the surface of carbon fiber changed from groove structure to pore structure.The effect of modification on "secondary structure" of glass fiber was that when the laser power was increased from 0W to 60W,the maximum depth of surface defects increased from 10nm to 50nm,the main range of surface defects increased from 5～8nm to 18-33nm,and the surface roughness(Rq)increased from 1.91nm to 8.10nm.The effect of modification on "secondary structure" of basalt fiber was that when the laser power was increased from 0 W to 120 W,the maximum depth of surface defects increased from 9nm to 180 nm,the main range of surface defects increased from 3.5～6.5nm to 90～120nm,and Rq increased from 1.41nm to 24.7nm.The effect of modification on "secondary structure" of carbon fiber could be expressed as two stages.At the first stage,when the laser power was increased from 0W to 210W,the maximum depth of surface defects decreased from 50nm to 7nm,the main range of surface defects decreased from 25～35nm to 3～5nm,and Rq decreased from 5.52nm to 1.26nm.At the second stage,when the laser power was increased from 210W to 240W,the maximum depth of surface defects increased from 7nm to 200nm,the main range of surface defects increased from 3～5nm to 125～175nm,and Rq increased from 1.26nm to 42.8nm.After laser modification,the tensile properties of the three fibers decreased,and the tensile strength accorded with the Weibull distribution.The tensile strength of glass fiber and basalt fiber decreased with the increase of surface defect depth,and the surface defect depth increased with the increase of modified power.Because the laser radiation has a special effect on the fibers,the relationship between surface defect depth(?)and tensile strength did not conform to the classical theory.Before and after laser modification,the XRD diffraction peak shape of the three fibers did not change,whereas the crystal size of the modified carbon fibers decreased.The surface chemical composition of the three fibers was not changed by laser modification.After the modification,the oxygen content on the surface of the modified fibers increased with the increase of the modification power.For laser surface modification,chemical modification is a secondary aspect.The higher the laser power was,the smaller the contact angle between the three fibers and epoxy resin was.The contact angle between glass fiber and epoxy resin decreased from 72.085° to 54.056° under the condition of 10mm·s-1 scanning rate and 50W modification power.The contact angle between basalt fiber and epoxy resin decreased from 68.82° to 55.012° at the scanning rate of 10mm·s-1 and modification power of 90W.The contact angle between carbon fiber and epoxy resin decreased from 65.973° to 50.832° at scanning rate of 1 mm·s-1 and modified power of 180W.Laser modification could improve the tensile strength and impact strength of fiber reinforced epoxy resin composites.When the glass fiber content was 0.7%and the modified power was 30W,the tensile strength of the composite reached the peak value of 58.71 MPa,which was 17.68%higher than that before modification.When the glass fiber content was 0.7%and the modified power was 60W,the impact strength of the composite reached the peak value of 38.7 KJ·m-2,which was 54.8%higher than that before modification.When the basalt fiber content was 4%and the laser power was 90W,the tensile strength of the composites reached a peak value of 78.23MPa,which was 15.2%higher than that before modification,and the impact strength reached a peak value of 36.7KJ·m-2,which was 31.5%higher than that before modification.When the carbon fiber content was 0.3%and the laser power was 150W,the tensile strength of the composite reached the peak value of 97.72MPa,which was 59%higher than that before modification,and the impact strength reached the peak value of 49.4KJ·m-2,which was 52%higher than that before modification. |
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