Ultrasonic experiment nondestructive testing technique application

一、 the meaning and purpose of experiments

Nondestructive testing technique is a applicable technical discipline that based on modern scientific technique,it has promise of destroying inside structure of object，use physical method,inspect physical properties ,condition property ,and inside structure of inside object or surface,inspect inside material whether has discontinuity (namely flaw ) ,and judge the objects are qualified or not, so as to assess its applicability。Currently common nondestructive testing technique includes rebound method measures concrete intensity,ultrasonic rebound comprehensive method measures concrete intensity，ultrasonic measures concrete inside flaw。

The experiment aim to know structure and principle of rebound machine and ultrasonic detector,control right ways of rebound machine and ultrasonic detector;control steps and methods of utilizing ultrasonic rebound comprehensive method to measure concrete intensity，control analysis of acoustic parameter nd judge fundamental method of internal flaw of concrete 。

By comparing practical compressive strength of concrete sample,analyzing affecting factors of nondestructive testing technique  。

二、 experiment principle

Rebound method is a heavy hammer that use spring loaded,by dowel bar ,rebound concrete surface,and measure distance that heavy hammer be rebounded,use rebound value as index that relevant intensity ,and infer concrete intensity,due to measurement is doing on the surface,so belongs to surface hardness method。

Rebound method measures concrete compressive strength ,is based on compressve strength of concrete has certain relation with rebound value。This relevance can be expressed by “FCU-r” relevant curve,relevant curve should satisfy measuring precision requirements,simpler and more convenient ,practical and wide usage range。

Ultrasonic rebound comprehensive method is means to adopt ultrasonic apparatus and rebound equipment,at same area of structure concrete measure rebound value,then utilize established formula to reckon concrete intensity fcu in this area。 Compare to single rebound or ultrasonic method,reduce effects of  time and water content,make up for inadequacy of each other，improve measuring precision。

Adopting ultrasonic pulse testing structure concrete flaw is according to :utilize travel time、receiving wave amplitude and frequency and other acoustic parameter of pulse wave in concrete with same conditions to judge concrete flaw。

三、 experiment device、flow process and instrument

Rebound instrument、ultrasonic detector、pressure testing machine

四、 experiment method and step 

(一) rebound method measures concrete intensity  

fix rebound machine on steel anvil,

Make sure value is between 80±2。

Put a set in all three concretes samples in order put middle line of press machine。

Open press machine,and exert 30-50KN constant pressure from concrete sample

Do rebound measurement to relative to side ,each side even set 8 testing point ,and record 16 rebound value。

In three parts on concrete sample measures carbonation depth of concrete sample,get average value as carbonation depth value of concrete sample。

Concrete intensity conversion table,make sure intensity conversion value of concrete sample 

On pressure testing machine,practically test this resist compression strength value of concrete sample 。

Compare intensity value difference of practical testing value and rebound method ,and analyzing reasons。

(二)ultrasonic rebound comprehensive methods to measure concrete intensity

Fix rebound instrument on steel anvil,make sure value is between 80±2

Put a group in all three concrete samples in order middle line of pressure machine 

Open up pressure machine,and exert 30-50KN constant pressure to concrete sample。   

Do rebound measurement to a side of sample,every side set 8 testing points evenly, in all record 16 points rebound value。

Draw circular domain on sides that Concrete sample didn’t rebound,and make sure when measuring, two converters axis can be in one line。

Circular domain painted coupling agent

Put converter aside of concrete coupling agent,slightly rotate and squeeze,make coupling agent even full of interval between converter and concrete surface。

Open ultrasonic detector,and enter interface

Entering parameter interface,set parameter values

Entering state interface,set parameter values

Entering sampling interface,press sampling key,when waveform is stable,press save key

In order measure concrete sample three testing sound speed。

According to above steps,measure rebound value and sound value of all samples。

Entering analyzing interface,choose test strength analysis,and input relevant strength parameter ,input rebound value。

System automatically calculate concrete intensity equivalent value

On press testing machine,practically test resist compression intensity value of this concrete sample

Compare to intensity value difference of being got by practical value and rebound method,and analyze reasons。

(三)measure concrete crack depth

Ultrasonic measurement concrete crack depth has many ways,including level measure method,inclined measurement method,hole drilling method,aim at different crack shapes,choose reasonable method to measure,and get accurate measuring value，The following is for example about level measure method,steps of ultrasonic detects concrete crack depth.

Put concrete with crack on experiment platform horizontally,make the side with crack upward。

At the same side of crack,make a ray that approximately parallel to crack,and make sure six points that has respectively distance 100.150.200.250.300.350mm 。

Paint coupling agent on above six points

Set ultrasonic detector parameter as not cross seam detection。

Put T,R converter respectively on both sides of crack,used determined six points as internal edge interval,in order measure acoustic value。

In above process,pay attention to head wave inverting phenomenon of receiving signal,analyzing what relationship between head wave and crack 。

Use “l “as longitudinal axis,”t” as horizontal axis to draw  L-T coordinate graphs, or use statistics law to get regression line between “t” and “l” l'=a+bt, each testing point ultrasonic real transmission distance l=l'+lal。