Contact Force Measurement And Damage Response Of Composite Laminates Subjected To Small-mass Impact

To develop the experimental technique on the damage resistance of laminates subjected to small mass impact,the tester for small mass impact was designed and manufactured.The wrench is used to drive the torsion spring to store the impact energy,then arm and impactor were activated by torsion spring.During the impact,the impactor and arm are in the approximate state of separated,which can simulate the impact of a free impactor.The fiber optic sensors are employed to measure impact velocity.The impact velocity may reach to 30 m/s,corresponding to the impact energy of 15 J,The contact force is measured with the acceleration,the strain of the impactor and the plate deflection of impact point respectively.Firstly,impact the force sensor to calibrate the strain gauge and acceleration sensor.It is shown the signal is disturbed by the axial vibration and resonance of the accelerometer and the contact force could be obtained with the filtered signals;but the calibration coefficient of strain is not unique,when the impactor structure changes,such as increase the threaded hole,it needs to be calibrated again.Impacts with variant energy were conducted on the laminates.It is shown the contact force measured through the deflection is in good agreement with the experimental one when there is no damage.When the distinct damage generated,the contact force measured by strain、acceleration sensors and laser displacement sensor drop at a special value in test that,then the force may increase again.It can be used to identify the delamination threshold load of small mass impact.And when the sampling rate of the impact point velocity is sufficient,it will also have sudden drop when delamination generated.Under the small impact energy subjected to small mass impact,the smaller impactor is,the greater contact force and the damage size.Duo to the damage form of large and small mass impact is different,the relationship between the damage width and residual compressive strength is not necessarily comparable,and the indentation of the later is inconspicuous,there are security risks.Under the intermediate-mass impact,the contact force measured by strain is not accurate because of self-interference.It is appropriate to measure by acceleration sensor.There is no manifest feature reflecting the delamination from the contact force of strain and acceleration.