Laravel - Belongs

I am doing a support system for courses and I am using the belongs for relationship, at the time of issuing the registration of students is not registering in the class and does not issue any error.

Codes

Model

<?php

namespace App;

use App\Turma;
use App\Trabalhos;
use InstagramAPI\Response\Model\Users;
use Illuminate\Notifications\Notifiable;
use Illuminate\Contracts\Auth\MustVerifyEmail;
use Illuminate\Foundation\Auth\User as Authenticatable;

class User extends Authenticatable
{
    use Notifiable;

    /**
     * The attributes that are mass assignable.
     *
     * @var array
    */

    protected $table = 'users';

    protected $fillable = [
        'name', 
        'email', 
        'password',
        'gender',
        'permission',
        'status',
        'telefone',
        'celular',
        'nascimento',
        'endereco',
        'cep'
    ];

    /**
     * The attributes that should be hidden for arrays.
     *
     * @var array
    */

    protected $hidden = [
        'password', 'remember_token', 'rg', 'cpf'
    ];

    public function trabalhos(){

        return $this->belongsToMany(Trabalhos::class, 'alunos_trb', 'aluno_id', 
        'trabalho_id');

    }

    public function turma(){

        return $this->belongsToMany(Turma::class, 'turma_usuarios', 
        'usuario_id', 'turma_id');
    }
}

Controller

public function cadastro(Request $request){

        $data = explode('/', $request->get('nascimento'));

        $dataNascimento = $data[2].'-'.$data[1].'-'.$data[0];

        Validator([
            'name' => 'required',
            'email' => 'required|email',
            'password' => 'required',
            'gender' => 'required',
            'telefone' => 'required|char',
            'celular' => 'required|char',
            'nascimento' => 'required',
            'endereco' => 'required',
            'cep' => 'required|char',
            'rg' => 'required|char',
            'cpf' => 'required|char',
            'turma' => 'required'
        ]);
        // print_r($request->turma);
        // die;
        try{
            DB::beginTransaction();
            $aluno = new User();
            $aluno->name = $request->name;
            $aluno->email = $request->email;
            $aluno->password = bcrypt($request->password);
            $aluno->gender = $request->gender;
            $aluno->telefone = $request->phone;
            $aluno->celular = $request->celular;
            $aluno->nascimento = $dataNascimento;
            $aluno->endereco = $request->endereco;
            $aluno->cep = $request->cep;
            $aluno->rg = $request->rg;
            $aluno->cpf = $request->cpf;
            $aluno->save();

            if(is_array($request->turma)){
                foreach( $request->turma as $m){
                    $turma = Turma::find($m);
                    $aluno->turma()->attach($turma);
                }
            }
            $aluno->save();

            DB::commit();
            return \Redirect::to('/alunos/lista');
        }catch(\Expension $e){
            DB::rollBack();
            return \Redirect::to('/alunos/lista');
        }


    }