QT connects two qslite databases and reports an error qsqlquery:: exec: database not open

QT Connect two qslite An error is reported when there is a data connection problem in the database QSqlQuery::exec: database not open
Two databases are two different interfaces , This is the code of one of the databases
Main function program
QSqlDatabase m_db=QSqlDatabase::addDatabase("QSQLITE","material_connect");
m_db.setDatabaseName("E:\Damage-assessment\software\QT\GUI\GUI4.0\gui1.0\build-gui-Desktop_Qt_5_14_2_MSVC2017_64bit-Release\mental_material.db");

        if(m_db.open())        {            qDebug()<<"open success1";        }        else        {            qDebug()<<"open failed1";        }         QSqlQueryModel *model=new QSqlQueryModel(this);             QString sql;             sql="select name as  full name  ,density as  density , shear_modulus as  shear modulus  ,yield_stress as  Yield stress , maximum_yield_stress as  Maximum yield stress , melting_temperature as  Melting temperature  from mental_material";             model->setQuery(sql,m_db);              ui->display->setModel(model);

Click the slot function of the button
void material::on_show_pushButton_clicked()
{
QSqlQueryModel *model=new QSqlQueryModel;
QString sql;
sql="select name as full name ,density as density , shear_modulus as shear modulus ,yield_stress as Yield stress , maximum_yield_stress as Maximum yield stress , melting_temperature as Melting temperature from mental_material";

 model->setQuery(sql,m_db); ui->display->setModel(model);

}

Operation results and error reporting contents

This is the picture after running

But click the display button , The database is gone

Report errors QSqlQuery::exec: database not open